draft-bertz-dime-rfc4006bis.xml

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<rfc category="std" docName="draft-ietf-dime-rfc4006bis-12" ipr="pre5378Trust200902" obsoletes="4006">


 <front>
   <title>Diameter Credit-Control Application</title>

   <author fullname="Lyle Bertz" initials="L." surname="Bertz" role="editor">
     <organization>Sprint</organization>
     <address>
       <postal>
         <street>6220 Sprint Parkway</street>
         <city>Overland Park</city>
         <region>KS</region>
         <code>66251</code>
         <country>United States</country>
       </postal>
       <email>lyleb551144@gmail.com</email>
     </address>
   </author>

   <author fullname="David Dolson" initials="D." surname="Dolson" role="editor">
     <organization>Sandvine</organization>
     <address>
       <postal>
         <street>408 Albert Street</street>
         <city>Waterloo</city>
         <region>ON</region>
         <code>N2L 3V3</code>
         <country>Canada</country>
       </postal>
       <email>ddolson@acm.org</email>
     </address>
   </author>

   <author fullname="Yuval Lifshitz" initials="Y." surname="Lifshitz" role="editor">
     <organization>Sandvine</organization>
     <address>
       <postal>
         <street>408 Albert Street</street>
         <city>Waterloo</city>
         <region>ON</region>
         <code>N2L 3V3</code>
         <country>Canada</country>
       </postal>
       <email>yuvalif@yahoo.com</email>
     </address>
   </author>

   <date year="2018"/>

   <area>General</area>

   <workgroup>Network Working Group</workgroup>

   <keyword>diameter</keyword>
   <keyword>charging</keyword>

   <abstract>
     <t>This document specifies a Diameter application that can be used to
   implement real-time credit-control for a variety of end user services
   such as network access, Session Initiation Protocol (SIP) services,
   messaging services, and download services. The Diameter Credit-Control application
   as defined in this document obsoletes RFC4006, and it must be supported by all new
   Diameter Credit-Control Application implementations.
</t>
   </abstract>
 </front>

 <middle>
   <section title="Introduction" anchor="intro">
	<t>
	   This document specifies a Diameter application that can be used to
	   implement real-time credit-control for a variety of end user services
	   such as network access, Session Initiation Protocol (SIP) services,
	   messaging services, and download services.  It provides a general
	   solution to real-time cost and credit-control.
	</t>
  <t>
	   The prepaid model has been shown to be very successful, for instance,
	   in GSM networks, where network operators offering prepaid services
	   have experienced a substantial growth of their customer base and
	   revenues.  Prepaid services are now cropping up in many other
	   wireless and wire line based networks.
	</t>
  <t>
	   In mobile networks, additional functionality is
	   required beyond that specified in the Diameter base protocol <xref target="RFC6733"/>.  For
	   example, the 3GPP Charging and Billing requirements <xref target="TGPPCHARG"/> state
	   that an application must be able to rate service information in
	   real-time.  In addition, it is necessary to check that the end user's
	   account provides coverage for the requested service prior to
	   initiation of that service.  When an account is exhausted or expired,
	   the user must be denied the ability to compile additional chargeable
	   events.
	</t><t>
	   A mechanism has to be provided to allow the user to be informed of
	   the charges to be levied for a requested service.  In addition, there
	   are services such as gaming and advertising that may credit as well
	   as debit a user account.
	</t><t>
	   The other Diameter applications provide service-specific
	   authorization, and they do not provide credit authorization for
	   prepaid users.  The credit authorization shall be generic and
	   applicable to all the service environments required to support
	   prepaid services.
	</t><t>
	   To fulfill these requirements, it is necessary to facilitate
           credit-control communication between the network element providing the
	   service (e.g., Network Access Server, SIP Proxy, and Application
	   Server) and a credit-control server.
	</t><t>
           The scope of this specification is the credit authorization.
           Service-specific authorization and authentication is out of scope.
	</t>

     <section title="Requirements Language">
       <t>
           The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
           NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
           "MAY", and "OPTIONAL" in this document are to be interpreted as
           described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they
           appear in all capitals, as shown here.
       </t>
     </section>

	<section anchor="terms" title="Terminology">
	  <t>
       <list style="hanging">
         <t hangText="AAA">
         Authentication, Authorization, and Accounting
         </t>
         <t hangText="AA answer">
         AA answer generically refers to a service-specific authorization and
         authentication answer.  AA answer commands are defined in service-specific 
         authorization applications, e.g., <xref target="RFC7155"/> and <xref target="RFC4004"/>.
         </t>
         <t hangText="AA request">
         AA request generically refers to a service-specific authorization and
         authentication request.  AA request commands are defined in service-specific 
         authorization applications e.g., <xref target="RFC7155"/> and <xref target="RFC4004"/>.
         </t>
         <t hangText="Credit-control">
         Credit-control is a mechanism that directly interacts in real-time
         with an account and controls or monitors the charges related to the
         service usage.  Credit-control is a process of checking whether
         credit is available, credit-reservation, deduction of credit from the
         end user account when service is completed and refunding of reserved
         credit that is not used.
         </t>
         <t hangText="Diameter Credit-control Server">
         A Diameter credit-control server acts as a prepaid server, performing
         real-time rating and credit-control.  It is located in the home
         domain and is accessed by service elements or Diameter AAA servers in
         real-time for purpose of price determination and credit-control
         before the service event is delivered to the end-user.  It may also
         interact with business support systems.
         </t>
         <t hangText="Diameter Credit-control Client">
         A Diameter credit-control client is an entity that interacts with a
         credit-control server.  It monitors the usage of the granted quota
         according to instructions returned by credit-control server.
         </t>
         <t hangText="Interrogation">
         The Diameter credit-control client uses interrogation to initiate a
         session based credit-control process.  During the credit-control
         process, it is used to report the used quota and request a new one.
         An interrogation maps to a request/answer transaction.
         </t>
         <t hangText="One-time event">
         Basically, a request/answer transaction of type event.
         </t>
         <t hangText="Rating">
         The act of determining the cost of the service event.
         </t>
         <t hangText="Service">
         A type of task performed by a service element for an end user.
         </t>
         <t hangText="Service Element">
         A network element that provides a service to the end users.  The
         Service Element may include the Diameter credit-control client, or
         another entity (e.g., RADIUS AAA server) that can act as a
         credit-control client on behalf of the Service Element.  In the latter case,
         the interface between the Service Element and the Diameter credit-control
         client is outside the scope of this specification.  Examples
         of the Service Elements include Network Access Server (NAS), SIP
         Proxy, and Application Servers such as messaging server, content
         server, and gaming server.
         </t>
         <t hangText="Service Event">
         An event relating to a service provided to the end user.
         </t>
         <t hangText="Session based credit-control">
         A credit-control process that makes use of several interrogations:
         the first, a possible intermediate, and the final.  The first
         interrogation is used to reserve money from the user's account and to
         initiate the process.  The intermediate interrogations may be needed
         to request new quota while the service is being rendered.  The final
         interrogation is used to exit the process.  The credit-control server
         is required to maintain session state for session-based credit-control.
         </t>

       </list>
      </t>
    </section>

	<section anchor="sec-1.3" title="Advertising Application Support">
	<t>
	   Diameter nodes conforming to this specification MUST advertise
	   support by including the value of 4 in the Auth-Application-Id of the
	   Capabilities-Exchange-Request and Capabilities-Exchange-Answer
    command <xref target="RFC6733"/>.
	</t>
	</section>
</section>

<section anchor="sec-2" title="Architecture Models">
<t>
   The current accounting models specified in the Radius Accounting
   <xref target="RFC2866"/> and Diameter base <xref target="RFC6733"/> are not sufficient for
   real-time credit-control, where credit-worthiness is to be determined
   prior to service initiation.  Also, the existing Diameter
   authorization applications, <xref target="RFC7155"/> and <xref target="RFC4004"/>, only provide
   service authorization, but do not provide credit authorization for
   prepaid users.  In order to support real-time credit-control, a new
   type of server is needed in the AAA infrastructure: Diameter credit-control
   server.  The Diameter credit-control server is the entity
   responsible for credit authorization for prepaid subscribers.
</t>
  <t>
   A service element may authenticate and authorize the end user with
   the AAA server by using AAA protocols; e.g., RADIUS or a Diameter
   base protocol with a possible Diameter application.
</t>
  <t>
   Accounting protocols such as RADIUS accounting and the Diameter base
   accounting protocol can be used to provide accounting data to the
   accounting server after service is initiated, and to provide possible
   interim reports until service completion.  However, for real-time
   credit-control, these authorization and accounting models are not
   sufficient.
</t>
  <t>
   When real-time credit-control is required, the credit-control client
   contacts the credit-control server with information about a possible
   service event.  The credit-control process is performed to determine
   potential charges and to verify whether the end user's account
   balance is sufficient to cover the cost of the service being
   rendered.
</t>
  <t>
   <xref target="fig-typical-cca"/> illustrates the typical credit-control architecture, which
   consists of a Service Element with an embedded Diameter credit-control
   client, a Diameter credit-control server, and an AAA server.
   A Business Support System is usually deployed; it includes at least
   the billing functionality.  The credit-control server and AAA server
   in this architecture model are logical entities.  The real
   configuration can combine them into a single host.  The credit-control
   protocol is the Diameter base protocol <xref target="RFC6733"/> with the Diameter
   credit-control application.
</t>
  <t>
   When an end user requests services such as SIP or messaging, the
   request is typically forwarded to a service element (e.g., SIP Proxy)
   in the user's home realm as defined in <xref target="RFC6733"/>.  In some cases it might be possible that
   the service element in the local realm <xref target="RFC6733"/> can offer services to the
   end user; however, a commercial agreement must exist between the
   local realm and the home realm.  Network access is an example of
   a service offered in the local realm where the NAS, through an AAA
   infrastructure, authenticates and authorizes the user with the user's
   home network.
</t>
  <figure title="Typical credit-control architecture" anchor="fig-typical-cca">
  <artwork><![CDATA[
               Service Element   AAA and CC
+----------+      +---------+     Protocols+-----------+  +--------+
|  End     |<---->|+-------+|<------------>|    AAA    |  |Business|
|  User    |   +->|| CC    ||              |   Server  |->|Support |
|          |   |  || Client||<-----+       |           |  |System  |
+----------+   |  |+-------+|      |       +-----------+  |        |
               |  +---------+      |             ^        +--------+
+----------+   |                   | CC Protocol |             ^
|  End     |<--+                   |       +-----v----+        |
|  User    |                       +------>|Credit-   |        |
+----------+                Credit-Control |Control   |--------+
                            Protocol       |Server    |
                                           +----------+
]]>
  </artwork>
  </figure>
<t>
   There can be multiple credit-control servers in the system for
   redundancy and load balancing.  The system can also contain separate
   rating server(s), and accounts can be located in a centralized
   database.  To ensure that the end user's account is not debited or
   credited multiple times for the same service event, only one place in
   the credit-control system should perform duplicate detection.  System
   internal interfaces can exist to relay messages between servers and
   an account manager.  However, the detailed architecture of the
   credit-control system and its interfaces are implementation specific
   and are out of scope of this specification.
</t>
  <t>
   Protocol transparent Diameter relays can exist between the credit-control
   client and credit-control server.  Also, Diameter Redirect
   agents that refer credit-control clients to credit-control servers
   and allow them to communicate directly can exist.  These agents
   transparently support the Diameter credit-control application.  The
   different roles of Diameter Agents are defined in Diameter base
   <xref target="RFC6733"/>, section 2.8.
</t>
  <t>
   If Diameter credit-control proxies exist between the credit-control
   client and the credit-control server, they MUST advertise the
   Diameter credit-control application support.
</t>
</section>

<section anchor="sec-3" title="Credit-Control Messages">
<t>
   This section defines new Diameter message Command-Code values that
   MUST be supported by all Diameter implementations that conform to
   this specification.  The Command Codes are as follows:
</t>
<texttable anchor="table_command_codes" title="Credit-Control Commands">
  <ttcol align="left">Command-Name</ttcol>
  <ttcol align="left">Abbrev.</ttcol>
  <ttcol align="left">Code</ttcol>
  <ttcol align="left">Reference</ttcol>
  <c>Credit-Control-Request</c><c>CCR</c><c>272</c><c>3.1</c>
  <c>Credit-Control-Answer</c><c>CCA</c><c>272</c><c>3.2</c>
</texttable>
<t>
   Diameter Base <xref target="RFC6733"/> defines in the section 3.2 the Command Code
   format specification.  These formats are observed in Credit-Control
   messages.
</t>
<section anchor="sec-3.1" title="Credit-Control-Request (CCR) Command">
<t>
   The Credit-Control-Request message (CCR) is indicated by the
   command-code field being set to 272 and the 'R' bit being set in the
   Command Flags field.  It is used between the Diameter credit-control
   client and the credit-control server to request credit authorization
   for a given service.
</t>
  <t>
   The Auth-Application-Id MUST be set to the value 4, indicating the
   Diameter credit-control application.
</t>
  <t>The CCR is extensible via the inclusion of one or more Attribute
      Value Pairs (AVPs).</t>
  <t>
   Message Format
</t>
<figure><artwork><![CDATA[
<Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
                             < Session-Id >
                             { Origin-Host }
                             { Origin-Realm }
                             { Destination-Realm }
                             { Auth-Application-Id }
                             { Service-Context-Id }
                             { CC-Request-Type }
                             { CC-Request-Number }
                             [ Destination-Host ]
                             [ User-Name ]
                             [ CC-Sub-Session-Id ]
                             [ Acct-Multi-Session-Id ]
                             [ Origin-State-Id ]
                             [ Event-Timestamp ]
                            *[ Subscription-Id ]
                            *[ Subscription-Id-Extension ]
                             [ Service-Identifier ]
                             [ Termination-Cause ]
                             [ Requested-Service-Unit ]
                             [ Requested-Action ]
                            *[ Used-Service-Unit ]
                             [ Multiple-Services-Indicator ]
                            *[ Multiple-Services-Credit-Control ]
                            *[ Service-Parameter-Info ]
                             [ CC-Correlation-Id ]
                             [ User-Equipment-Info ]
                             [ User-Equipment-Info-Extension ]
                            *[ Proxy-Info ]
                            *[ Route-Record ]
                            *[ AVP ]
]]>
        </artwork>
      </figure>
  </section>
<section anchor="sec-3.2" title="Credit-Control-Answer (CCA) Command">
<t>
   The Credit-Control-Answer message (CCA) is indicated by the command-code
   field being set to 272 and the 'R' bit being cleared in the
   Command Flags field.  It is used between the credit-control server
   and the Diameter credit-control client to acknowledge a Credit-Control-Request
   command.
</t>
  <t>
   Message Format
</t>
<figure>
<artwork><![CDATA[
     <Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
                                 < Session-Id >
                                 { Result-Code }
                                 { Origin-Host }
                                 { Origin-Realm }
                                 { Auth-Application-Id }
                                 { CC-Request-Type }
                                 { CC-Request-Number }
                                 [ User-Name ]
                                 [ CC-Session-Failover ]
                                 [ CC-Sub-Session-Id ]
                                 [ Acct-Multi-Session-Id ]
                                 [ Origin-State-Id ]
                                 [ Event-Timestamp ]
                                 [ Granted-Service-Unit ]
                                *[ Multiple-Services-Credit-Control ]
                                 [ Cost-Information]
                                 [ Final-Unit-Indication ]
                                 [ QoS-Final-Unit-Indication ]
                                 [ Check-Balance-Result ]
                                 [ Credit-Control-Failure-Handling ]
                                 [ Direct-Debiting-Failure-Handling ]
                                 [ Validity-Time ]
                                *[ Redirect-Host ]
                                 [ Redirect-Host-Usage ]
                                 [ Redirect-Max-Cache-Time ]
                                *[ Proxy-Info ]
                                *[ Route-Record ]
                                *[ Failed-AVP ]
                                *[ AVP ]
]]>
      </artwork>
  </figure>
</section>
</section>
<section anchor="sec-4" title="Credit-Control Application Overview">
<t>
   The credit authorization process takes place before and during
   service delivery to the end user and generally requires the user's
   authentication and authorization before any request is sent to the
   credit-control server.  The credit-control application defined in
   this specification supports two different credit authorization
   models: credit authorization with money reservation and credit
   authorization with direct debiting.  In both models, the credit-control
   client requests credit authorization from the credit-control
   server prior to allowing any service to be delivered to the end user.
</t>
  <t>
   In the first model, the credit-control server rates the request,
   reserves a suitable amount of money from the user's account, and
   returns the amount of credit reserved.  Note that
   credit resources may not imply actual monetary credit; credit
   resources may be granted to the credit-control client in the form of
   units (e.g., data volume or time) to be metered.
</t>
  <t>
   Upon receipt of a successful credit authorization answer with a
   certain amount of credit resources, the credit-control client allows
   service delivery to the end user and starts monitoring the usage of
   the granted resources.  When the credit resources granted to the user
   have been consumed or the service has been successfully delivered or
   terminated, the credit-control client reports back to the server the
   used amount.  The credit-control server deducts the used amount from
   the end user's account; it may perform rating and make a new credit
   reservation if the service delivery is continuing.  This process is
   accomplished with session based credit-control that includes the
   first interrogation, possible intermediate interrogations, and the
   final interrogation.  For session based credit-control, both the
   credit-control client and the credit-control server are required to
   maintain credit-control session state.  Session based credit-control
   is described in more detail, with more variations, in <xref target="sec-5"/>.
</t>
  <t>
   In contrast, credit authorization with direct debiting is a single
   transaction process wherein the credit-control server directly
   deducts a suitable amount of money from the user's account as soon as
   the credit authorization request is received.  Upon receipt of a
   successful credit authorization answer, the credit-control client
   allows service delivery to the end user.  This process is
   accomplished with the one-time event.  Session state is not
   maintained.
</t>
  <t>
   In a multi-service environment, an end user can issue an additional
   service request (e.g., data service) during an ongoing service (e.g.,
   voice call) toward the same account.  Alternatively, during an active
   multimedia session, an additional media type is added to the session,
   causing a new simultaneous request toward same account.
   Consequently, this needs to be considered when credit resources are
   granted to the services.
</t>
  <t>
   The credit-control application also supports operations such as
   service price enquiry, user's balance check, and refund of credit on
   the user's account.  These operations are accomplished with the
   one-time event.  Session state is not maintained.
</t>
  <t>
   Flexible failure handling, specific to the credit-control, is
   defined in the application. This allows the the service provider
   to control the credit-control client behavior according to its own
   risk management policy.
</t>
  <t>
   The Credit-Control-Failure-Handling AVP and the Direct-Debiting-Failure-Handling
   AVP are defined to determine what is done if the
   sending of credit-control messages to the credit-control server has
   been temporarily prevented.  The usage of the Credit-Control-Failure-Handling
   AVP and the Direct-Debiting-Failure-Handling AVP
   allows flexibility, as failure handling for the credit-control
   session and one-time event direct debiting may be different.
</t>
<section anchor="sec-4.1" title="Service-Specific Rating Input and Interoperability">
<t>
   The Diameter credit-control application defines the framework for
   credit-control; it provides generic credit-control mechanisms
   supporting multiple service applications.  The credit-control
   application, therefore, does not define AVPs that could be used as
   input in the rating process.  Listing the possible services that
   could use this Diameter application is out of scope for this generic
   mechanism.
</t>
  <t>
   It is reasonable to expect that a service level agreement will exist
   between providers of the credit-control client and the credit-control
   server covering the charging, services offered, roaming agreements,
   agreed rating input (i.e., AVPs), and so on.
</t>
  <t>
   Therefore, it is assumed that a Diameter credit-control server will
   provide service only for Diameter credit-control clients that have
   agreed beforehand as to the content of credit-control messages.
   Naturally, it is possible that any arbitrary Diameter credit-control
   client can interchange credit-control messages with any Diameter
   credit-control server, but with a higher likelihood that unsupported
   services/AVPs could be present in the credit-control message, causing
   the server to reject the request with an appropriate result-code.
</t>
<section anchor="sec-4.1.1" title="Specifying Rating Input AVPs">
<t>
   There are two ways to provide rating input to the credit-control
   server: either by using AVPs or by including them in the Service-Parameter-Info
   AVP.  The general principles for sending rating
   parameters are as follows:
</t>
  <t>
   1a. The service SHOULD re-use existing AVPs if it can use AVPs
   defined in existing Diameter applications (e.g., <xref target="RFC7155"/>
   for network
   access services).  Re-use of existing AVPs is strongly recommended in
   <xref target="RFC6733"/>.
</t>
  <t>
   For AVPs of type Enumerated, the service may require a new value to
   be defined.  Allocation of new AVP values is done as specified in
   <xref target="RFC6733"/>, section 1.3.
</t>
  <t>
   1b. New AVPs can be defined if the existing AVPs do not provide
   sufficient rating information.  In this case, the procedures defined
   in <xref target="RFC6733"/> for creating new AVPs MUST be followed.
</t><t>
   1c. For services specific only to one vendor's implementation, a
   Vendor-Specific AVP code for Private use can be used.  Where a
   Vendor-Specific AVP is implemented by more than one vendor,
   allocation of global AVPs is encouraged instead; refer to <xref target="RFC6733"/>.
</t>
  <t>
   2. The Service-Parameter-Info AVP MAY be used as a container to pass
   legacy rating information in its original encoded form (e.g., ASN.1
   BER).  This method can be used to avoid unnecessary conversions from
   an existing data format to an AVP format.  In this case, the rating
   input is embedded in the Service-Parameter-Info AVP as defined in
   <xref target="sec-8.43"/>.
</t>
  <t>
   New service applications SHOULD favor the use of explicitly defined
   AVPs as described in items 1a and 1b, to simplify interoperability.
</t>
</section>
<section anchor="sec-4.1.2" title="Service-Specific Documentation">
<t>
   The service-specific rating input AVPs, the contents of the Service-Parameter-Info
   AVP or Service-Context-Id AVP (defined in <xref target="sec-8.42"/>)
   are not within the scope of this document. To facilitate interoperability,
   it is RECOMMENDED that the rating input and the values of the
   Service-Context-Id be coordinated via an informational RFC or other
   permanent and readily available reference, preferably, of another
   cooperative standardization body (e.g., 3GPP, OMA, or 3GPP2). However,
   private services may be deployed that are subject to agreements
   between providers of the credit-control server and client.  In
   this case, vendor-specific AVPs can be used.
</t>
  <t>
   This specification, together with the above service-specific
   documents, governs the credit-control message.  Service-specific
   documents define which existing AVPs or new AVPs are used as input to
   the rating process (i.e., those that do not define new credit-control
   applications), and thus have to be included in the Credit-Control-Request
   command by a Diameter credit-control client supporting a
   given service as *[AVP].  Should Service-Parameter-Info be used, then
   the service-specific document MUST specify the exact content of this
   grouped AVP.
</t>
  <t>
   The Service-Context-Id AVP MUST be included at the command level of a
   Credit-Control Request to identify the service-specific document that
   applies to the request.  The specific service or rating group the
   request relates to is uniquely identified by the combination of
   Service-Context-Id and Service-Identifier or Rating-Group.
</t>
</section>
<section anchor="sec-4.1.3" title="Handling of Unsupported/Incorrect Rating Input">
<t>
   Diameter credit-control implementations are required to support the
   Mandatory rating AVPs defined in service-specific documentation of
   the services they support, according to the 'M' bit rules in
   <xref target="RFC6733"/>.
</t>
  <t>
   If a rating input required for the rating process is incorrect in the
   Credit-control request, or if the credit-control server does not
   support the requested service context (identified by the Service-Context-Id
   AVP at command level), the Credit-control answer MUST
   contain the error code DIAMETER_RATING_FAILED.  A CCA message with
   this error MUST contain one or more Failed-AVP AVPs containing the
   missing and/or unsupported AVPs that caused the failure.  A Diameter
   credit-control client that receives the error code
   DIAMETER_RATING_FAILED in response to a request MUST NOT send similar
   requests in the future.
</t>
</section>
<section anchor="sec-4.1.4" title="RADIUS Vendor-Specific Rating Attributes">
<t>
   When service-specific documents include RADIUS vendor-specific
   attributes that could be used as input in the rating process, the
   rules described in <xref target="RFC7155"/> for formatting the Diameter AVP MUST be
   followed.
</t>
  <t>
   For example, if the AVP code used is the vendor attribute type code,
   the Vendor-Specific flag MUST be set to 1 and the Vendor-ID MUST be
   set to the IANA Vendor identification value.  The Diameter AVP data
   field contains only the attribute value of the RADIUS attribute.
</t>
    </section>
  </section>
</section>
<section anchor="sec-5" title="Session Based Credit-Control">
<section anchor="sec-5.1" title="General Principles">
<t>
   For a session-based credit-control, several interrogations are
   needed: the first, intermediate (optional) and the final
   interrogations.  This is illustrated in
   <xref target="first_interrogation"/> and
   <xref target="first_interrogation_auth"/>.
</t>
<t>
   If the credit-control client performs credit-reservation before
   granting service to the end user, it MUST use several interrogations
   toward the credit-control server (i.e., session based credit-control).
   In this case, the credit-control server MUST maintain the
   credit-control session state.
</t>
<t>
   Each credit-control session MUST have a globally unique Session-Id as
   defined in <xref target="RFC6733"/>, which MUST NOT be
   changed during the lifetime of a credit-control session.
</t>
<t>
   Certain applications require multiple credit-control sub-sessions.
   These applications would send messages with a constant Session-Id
   AVP, but with a different CC-Sub-Session-Id AVP.  If several credit
   sub-sessions will be used, all sub-sessions MUST be closed separately
   before the main session is closed so that units per sub-session may
   be reported.  The absence of this AVP implies that no sub-sessions
   are in use.
</t>
<t>
   Note that the service element might send a service-specific
   re-authorization message to the AAA server due to expiration of the
   authorization-lifetime during an ongoing credit-control session.
   However, the service-specific re-authorization does not influence the
   credit authorization that is ongoing between the credit-control
   client and credit-control server, as credit authorization is
   controlled by the burning rate of the granted quota.
</t>
<t>
   If service-specific re-authorization fails, the user will be
   disconnected, and the credit-control client MUST send a final
   interrogation to the credit-control server.
</t>
<t>
   The Diameter credit-control server may seek to control the validity
   time of the granted quota and/or the production of intermediate
   interrogations.  Thus, it MAY include the Validity-Time AVP in the
   answer message to the credit-control client.  Upon expiration of the
   Validity-Time, the credit-control client MUST generate a credit-control
   update request and report the used quota to the credit-control server.
   It is up to the credit-control server to determine
   the value of the Validity-Time to be used for consumption of the
   granted service unit(s) (G-S-U).  If the Validity-Time is used, its value
   SHOULD be given as input to set the session supervision timer Tcc
   (the session supervision timer MAY be set to two times the value of
   the Validity-Time, as defined in <xref target="sec-13"/>).  Since credit-control
   update requests are also produced at the expiry of granted service
   units and/or for mid-session service events, the omission of
   Validity-Time does not mean that intermediate interrogation for the
   purpose of credit-control is not performed.
</t>
<section anchor="sec-5.1.1" title="Basic Tariff-Time Change Support">
<t>
   The Diameter credit-control server and client MAY optionally support
   a tariff change mechanism.  The Diameter credit-control server may
   include a Tariff-Time-Change AVP in the answer message.  Note that
   the granted units should be allocated based on the worst-case
   scenario in case of forthcoming tariff change, so that the overall
   reported used units would never exceed the credit reservation.
</t>
<t>
   When the Diameter credit-control client reports the used units and a
   tariff change has occurred during the reporting period, the Diameter
   credit-control client MUST separately itemize the units used before
   and after the tariff change.  If the client is unable to distinguish
   whether units straddling the tariff change were used before or after
   the tariff change, the credit-control client MUST itemize those units
   in a third category.
</t>
<t>
   If a client does not support the tariff change mechanism and it
   receives a CCA message carrying the Tariff-Time-Change AVP, it MUST
   terminate the credit-control session, giving a reason of
   DIAMETER_BAD_ANSWER in the Termination-Cause AVP.
</t>
<t>
   For time based services, the quota is continuously consumed at the
   regular rate of 60 seconds per minute (ignoring leap seconds).  At the time when credit
   resources are allocated, the server already knows how many units will
   be consumed before the tariff time change and how many units will be
   consumed afterward.  Similarly, the server can determine the units
   consumed at the before rate and the units consumed at the rate
   afterward in the event that the end-user closes the session before
   the consumption of the allotted quota.  There is no need for
   additional traffic between client and server in the case of tariff
   time changes for continuous time based service.  Therefore, the
   tariff change mechanism is not used for such services.  For time-based
   services in which the quota is NOT continuously consumed at a
   regular rate, the tariff change mechanism described for volume and
   event units MAY be used.
</t>
</section>
<section anchor="sec-5.1.2" title="Credit-Control for Multiple Services within a (sub-)Session">
<t>
   When multiple services are used within the same user session and each
   service or group of services is subject to different cost, it is
   necessary to perform credit-control for each service independently.
   Making use of credit-control sub-sessions to achieve independent
   credit-control will result in increased signaling load and usage of
   resources in both the credit-control client and the credit-control
   server.  For instance, during one network access session the end user
   may use several http-services subject to different access cost.  The
   network-access-specific attributes such as the quality of service
   (QoS) are common to all the services carried within the access
   bearer, but the cost of the bearer may vary depending on its content.
</t>
<t>
   To support these scenarios optimally, the credit-control application
   enables independent credit-control of multiple services in a single
   credit-control (sub-)session.  This is achieved by including the
   optional Multiple-Services-Credit-Control AVP in Credit-Control-Request/Answer
   messages.  It is possible to request and allocate
   resources as a credit pool shared between multiple services.  The
   services can be grouped into rating groups in order to achieve even
   further aggregation of credit allocation.  It is also possible to
   request and allocate quotas on a per service basis.  Where quotas are
   allocated to a pool by means of the Multiple-Services-Credit-Control
   AVP, the quotas remain independent objects that can be re-authorized
   independently at any time.  Quotas can also be given independent
   result codes, validity times, and Final-Unit-Indications
   or QoS-Final-Unit-Indications.
</t>
<t>
   A Rating-Group gathers a set of services, identified by a Service-Identifier,
   and subject to the same cost and rating type (e.g.,
   $0.1/minute).  It is assumed that the service element is provided
   with Rating-Groups, Service-Identifiers, and their associated
   parameters that define what has to be metered by means outside the
   scope of this specification.  (Examples of parameters associated to
   Service-Identifiers are IP 5-tuple and HTTP URL.) Service-Identifiers
   enable authorization on a per-service based credit as well as
   itemized reporting of service usage.  It is up to the credit-control
   server whether to authorize credit for one or more services or for
   the whole rating-group.  However, the client SHOULD always report
   used units at the finest supported level of granularity.  Where quota
   is allocated to a rating-group, all the services belonging to that
   group draw from the allotted quota.  The following is a graphical
   representation of the relationship between service-identifiers,
   rating-groups, credit pools, and credit-control (sub-)session.
</t>
<figure title="Multiple-Service (sub)-Session Example" anchor="multiservice">
<artwork><![CDATA[
                        DCC (Sub-)Session
                                |
      +------------+-----------+-------------+--------------- +
      |            |           |             |                |
Service-Id a Service-Id b Service-Id c Service-Id d.....Service-Id z
      \        /                 \         /                /
       \      /                   \       /                /
        \    /                  Rating-Group 1.......Rating-Group n
         \  /                         |                    |
        Quota       ---------------Quota                 Quota
          |        /                                       |
          |       /                                        |
       Credit-Pool                                    Credit-Pool
]]>
      </artwork>
</figure>
<t>
   If independent credit-control of multiple services is used, the
   Validity-Time AVP and Final-Unit-Indication AVP or QoS-Final-Unit-Indication AVP
   SHOULD be present either in the Multiple-Services-Credit-Control AVP(s) or at
   command level as single AVPs.  However, the Result-Code AVP MAY be present
   both on the command level and within the Multiple-Services-Credit-Control AVP.
   If the Result-Code AVP on the command level indicates a value other than
   SUCCESS, then the Result-Code AVP on command level takes precedence over
   any included in the Multiple-Services-Credit-Control AVP.
</t>
<t>
   The credit-control client MUST indicate support for independent
   credit-control of multiple services within a (sub-)session by
   including the Multiple-Services-Indicator AVP in the first
   interrogation.  A credit-control server not supporting this feature
   MUST treat the Multiple-Services-Indicator AVP and any received
   Multiple-Services-Credit-Control AVPs as invalid AVPs.
</t>
<t>
   If the client indicated support for independent credit-control of
   multiple services, a credit-control server that wishes to use the
   feature MUST return the granted units within the Multiple-Services-Credit-Control
   AVP associated to the corresponding service-identifier
   and/or rating-group.
</t>
<t>
   To avoid a situation where several parallel (and typically also
   small) credit reservations must be made on the same account (i.e.,
   credit fragmentation), and also to avoid unnecessary load on the
   credit-control server, it is possible to provide service units as a
   pool that applies to multiple services or rating groups.  This is
   achieved by providing the service units in the form of a quota for a
   particular service or rating group in the Multiple-Services-Credit-Control
   AVP, and also by including a reference to a credit pool for
   that unit type.
</t>
<t>
   The reference includes a multiplier derived from the rating
   parameter, which translates from service units of a specific type to
   the abstract service units in the pool.  For instance, if the rating
   parameter for service 1 is $1/MB and the rating parameter for service
   2 is $0.5/MB, the multipliers could be 10 and 5 for services 1 and 2,
   respectively.
</t>
<t>
   If S is the total service units within the pool, M1, M2, ..., Mn are
   the multipliers provided for services 1, 2, ..., n, and C1, C2, ...,
   Cn are the used resources within the session, then the pool credit is
   exhausted and re-authorization MUST be sought when:
</t>
<figure>
<artwork><![CDATA[
         C1*M1 + C2*M2 + ... + Cn*Mn >= S
]]></artwork>
</figure>
<t>
   The total credit in the pool, S, is calculated from the quotas, which
   are currently allocated to the pool as follows:
</t>
<figure>
<artwork><![CDATA[
         S = Q1*M1 + Q2*M2 + ... + Qn*Mn
]]></artwork>
</figure>
<t>
   If services or rating groups are added to or removed from the pool,
   then the total credit is adjusted appropriately.  Note that when the
   total credit is adjusted because services or rating groups are
   removed from the pool, the value that need to be removed is the
   consumed one (i.e., Cx*Mx).
</t>
<t>
   Re-authorizations for an individual service or rating group may be
   sought at any time; for example, if a 'non-pooled' quota is used up
   or the Validity-Time expires.
</t>
<t>
   Where multiple G-S-U-Pool-Reference AVPs (<xref target="sec-8.30"/>) with the same
   G-S-U-Pool-Identifier are provided within a Multiple-Services-Credit-Control
   AVP (<xref target="sec-8.16"/>) along with the Granted-Service-Unit
   AVP, then these MUST have different CC-Unit-Type values, and they all
   draw from the credit pool separately.  For instance, if one
   multiplier for time (M1t) and one multiplier for volume (M1v) are
   given, then the used resources from the pool is the sum C1t*M1t +
   C1v*M1v, where C1t is the time unit and C1v is the volume unit.
</t>
<t>
   Where service units are provided within a Multiple-Services-Credit-Control
   AVP without a corresponding G-S-U-Pool-Reference AVP, then
   these are handled independently from any credit pool and from any
   other services or rating groups within the session.
</t>
<t>
   The credit pool concept is an optimal tool to avoid the over-reservation
   effect of the basic single quota tariff time change
   mechanism (the mechanism described in <xref target="sec-5.1.1"/>).  Therefore,
   Diameter credit-control clients and servers implementing the
   independent credit-control of multiple services SHOULD leverage the
   credit pool concept when supporting the tariff time change.  The
   Diameter credit-control server SHOULD include both the Tariff-Time-Change
   and Tariff-Change-Usage AVPs in two quota allocations in the
   answer message (i.e., two instances of the Multiple-Services-Credit-Control
   AVP).  One of the granted units is allocated to be used
   before the potential tariff change, while the second granted units
   are for use after a tariff change.  Both granted unit quotas MUST
   contain the same Service-Identifier and/or Rating-Group.  This dual
   quota mechanism ensures that the overall reported used units would
   never exceed the credit reservation.  The Diameter credit-control
   client reports both the used units before and after the tariff change
   in a single instance of the Multiple-Services-Credit-Control AVP.
</t>
<t>
   The failure handling for credit-control sessions is defined in
   <xref target="sec-5.7"/> and reflected in the basic credit-control state machine
   in <xref target="sec-7"/>.  Credit-control clients and servers implementing the
   independent credit-control of multiple services in a (sub-)session
   functionality MUST ensure failure handling and general behavior fully
   consistent with the above mentioned sections, while maintaining the
   ability to handle parallel ongoing credit re-authorization within a
   (sub-)session.  Therefore, it is RECOMMENDED that Diameter credit-control
   clients maintain a PendingU message queue and restart the Tx
   timer (<xref target="sec-13"/>) every time a CCR message with the value
   UPDATE_REQUEST is sent while they are in PendingU state.  When
   answers to all pending messages are received, the state machine moves
   to OPEN state, and Tx timer is stopped.  Naturally, the action performed
   when a problem for the session is detected according to <xref target="sec-5.7"/>
   affects all the ongoing services (e.g., failover to a backup server
   if possible affect all the CCR messages with the value UPDATE_REQUEST
   in the PendingU queue).
</t>
<t>
   Since the client may send CCR messages with the value UPDATE_REQUEST
   while in PendingU (i.e., without waiting for an answer to ongoing
   credit re-authorization), the time space between these requests may
   be very short, and the server may not have received the previous
   request(s) yet.  Therefore, in this situation the server may receive
   out of sequence requests and SHOULD NOT consider this an error
   condition.  A proper answer is to be returned to each of those
   requests.
</t>
  </section>
</section>
<section anchor="sec-5.2" title="First Interrogation">
<t>
   When session based credit-control is required (e.g., the
   authentication server indicated a prepaid user), the first
   interrogation MUST be sent before the Diameter credit-control client
   allows any service event to the end user.  The CC-Request-Type is set
   to the value INITIAL_REQUEST in the request message.
</t>
<t>
   If the Diameter credit-control client knows the cost of the service
   event (e.g., a content server delivering ringing tones may know their
   cost) the monetary amount to be charged is included in the
   Requested-Service-Unit AVP.  If the Diameter credit-control client
   does not know the cost of the service event, the Requested-Service-Unit
   AVP MAY contain the number of requested service events.  Where
   the Multiple-Services-Credit-Control AVP is used, it MUST contain the
   Requested-Service-Unit AVP to indicate that the quota for the
   associated service/rating-group is requested.  In the case of
   multiple services, the Service-Identifier AVP or the Rating-Group AVP
   within the Multiple-Services-Credit-Control AVP always indicates the
   service concerned.  Additional service event information to be rated
   MAY be sent as service-specific AVPs or MAY be sent within the
   Service-Parameter-Info AVP at command level.  The Service-Context-Id
   AVP indicates the service-specific document applicable to the
   request.
</t>
<t>
   The Event-Timestamp AVP SHOULD be included in the request and
   contains the time when the service event is requested in the service
   element.  The Subscription-Id AVP or the Subscription-Id-Extension AVP
   SHOULD be included to identify the end user in the credit-control server.
   The credit-control client MAY include the User-Equipment-Info AVP or
   User-Equipment-Info-Extension AVP so that the credit-control server has some
   indication of the type and capabilities of the end user access device.
   How the credit-control server uses this information is outside the scope
   of this document.
</t>
<t>
   The credit-control server SHOULD rate the service event and make a
   credit-reservation from the end user's account that covers the cost
   of the service event.  If the type of the Requested-Service-Unit AVP
   is money, no rating is needed, but the corresponding monetary amount
   is reserved from the end user's account.
</t>
<t>
   The credit-control server returns the Granted-Service-Unit AVP in the
   Answer message to the Diameter credit-control client.  The Granted-Service-Unit
   AVP contains the amount of service units that the
   Diameter credit-control client can provide to the end user until a
   new Credit-Control-Request MUST be sent to the credit-control server.
   If several unit types are sent in the Answer message, the credit-control
   client MUST handle each unit type separately.  The type of
   the Granted-Service-Unit AVP can be time, volume, service-specific,
   or money, depending on the type of service event.  The unit type(s)
   SHOULD NOT be changed within an ongoing credit-control session.
</t>
<t>
   There MUST be a maximum of one instance of the same unit type in one
   Answer message.  However, if multiple quotas are conveyed to the
   credit-control client in the Multiple-Services-Credit-Control AVPs,
   it is possible to carry two instances of the same unit type
   associated to a service-identifier/rating-group.  This is typically
   the case when a tariff time change is expected and the credit-control
   server wants to make a distinction between the granted quota before
   and after tariff change.
</t>
<t>
   If the credit-control server determines that no further control is
   needed for the service, it MAY include the result code indicating
   that the credit-control is not applicable (e.g., if the service is
   free of charge).  This result code at command level implies that the
   credit-control session is to be terminated.
</t>
<t>
   The Credit-Control-Answer message MAY also include the Final-Unit-Indication
   AVP or the QoS-Final-Unit-Indication AVP to indicate that the answer
   message contains the final units for the service.  After the end user has
   consumed these units, the Diameter credit-control-client MUST behave as
   described in <xref target="sec-5.6"/>.
</t>
<t>
   This document defines two different approaches to perform the first
   interrogation to be used in different network architectures.  The
   first approach uses credit-control messages after the user's
   authorization and authentication takes place.  The second approach
   uses service-specific authorization messages to perform the first
   interrogation during the user's authorization/authentication phase,
   and credit-control messages for the intermediate and final
   interrogations.  If an implementation of the credit-control client
   supports both the methods, determining which method to use SHOULD be
   configurable.
</t>
<t>
   In service environments such as the Network Access Server (NAS), it
   is desired to perform the first interrogation as part of the
   authorization/authentication process for the sake of protocol
   efficiency.  Further credit authorizations after the first
   interrogation are performed with credit-control commands defined in
   this specification.  Implementations of credit-control clients
   operating in the mentioned environments SHOULD support this method.
   If the credit-control server and AAA server are separate physical
   entities, the service element sends the request messages to the AAA
   server, which then issues an appropriate request or proxies the
   received request forward to the credit-control server.
</t>
<t>
   In other service environments, such as the 3GPP network and some SIP
   scenarios, there is a substantial decoupling between
   registration/access to the network and the actual service request
   (i.e., the authentication/authorization is executed once at
   registration/access to the network and is not executed for every
   service event requested by the subscriber).  In these environments,
   it is more appropriate to perform the first interrogation after the
   user has been authenticated and authorized.  The first, the
   intermediate, and the final interrogations are executed with credit-control
   commands defined in this specification.
</t>
<t>
   Other IETF standards or standards developed by other standardization
   bodies may define the most suitable method in their architectures.
</t>
<section anchor="sec-5.2.1" title="First Interrogation after Authorization and Authentication">
<t>
   The Diameter credit-control client in the service element may get
   information from the authorization server as to whether credit-control
   is required, based on its knowledge of the end user.  If
   credit-control is required the credit-control server needs to be
   contacted prior to initiating service delivery to the end user.  The
   accounting protocol and the credit-control protocol can be used in
   parallel.  The authorization server may also determine whether the
   parallel accounting stream is required.
</t>
<t>
   The following diagram illustrates the case where both protocols are
   used in parallel and the service element sends credit-control
   messages directly to the credit-control server.  More credit-control
   sequence examples are given in Annex A.
</t>
<figure align="center" title="Protocol example with first interrogation after user's authorization/authentication"
        anchor="first_interrogation">
<artwork><![CDATA[
                                           Diameter
End User        Service Element        AAA Server         CC Server
                   (CC Client)
    | Registration      | AA request/answer(accounting,cc or both)|
    |<----------------->|<------------------>|                    |
    |        :          |                    |                    |
    |        :          |                    |                    |
    | Service Request   |                    |                    |
    |------------------>|                    |                    |
    |                   | CCR(Initial,Credit-Control AVPs)        |
    |                  +|---------------------------------------->|
    |         CC stream||                    |  CCA(Granted-Units)|
    |                  +|<----------------------------------------|
    | Service Delivery  |                    |                    |
    |<----------------->| ACR(start,Accounting AVPs)              |
    |         :         |------------------->|+                   |
    |         :         |                ACA || Accounting stream |
    |                   |<-------------------|+                   |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |                   | CCR(Update,Used-Units)                  |
    |                   |---------------------------------------->|
    |                   |                    |  CCA(Granted-Units)|
    |                   |<----------------------------------------|
    |         :         |                    |                    |
    |         :         |                    |                    |
    | End of Service    |                    |                    |
    |------------------>| CCR(Termination, Used-Units)            |
    |                   |---------------------------------------->|
    |                   |                    |               CCA  |
    |                   |<----------------------------------------|
    |                   | ACR(stop)          |                    |
    |                   |------------------->|                    |
    |                   |                ACA |                    |
    |                   |<-------------------|                    |
  ]]></artwork>
</figure>
</section>
<section anchor="sec-5.2.2" title="First Interrogation Included with Authorization Messages">
<t>
   The Diameter credit-control client in the service element MUST
   actively co-operate with the authorization/authentication client in
   the construction of the AA request by adding appropriate credit-control AVPs.
   The credit-control client MUST add the Credit-Control
   AVP to indicate credit-control capabilities and MAY add other
   relevant credit-control-specific AVPs to the proper
   authorization/authentication command to perform the first
   interrogation toward the home Diameter AAA server.  The Auth-Application-Id
   is set to the appropriate value, as defined in the
   relevant service-specific authorization/authentication application
   document (e.g., <xref target="RFC7155"/>, <xref target="RFC4004"/>).  The home Diameter AAA server
   authenticates/authorizes the subscriber and determines whether
   credit-control is required.
</t>
<t>
   If credit-control is not required for the subscriber, the home
   Diameter AAA server will respond as usual, with an appropriate AA
   answer message.  If credit-control is required for the subscriber and
   the Credit-Control AVP with the value set to CREDIT_AUTHORIZATION was
   present in the authorization request, the home AAA server MUST
   contact the credit-control server to perform the first interrogation.
   If credit-control is required for the subscriber and the Credit-Control
   AVP was not present in the authorization request, the home
   AAA server MUST send an authorization reject answer message.
</t>
<t>
   The Diameter AAA server supporting credit-control is required to send
   the Credit-Control-Request command (CCR) defined in this document to
   the credit-control server.  The Diameter AAA server populates the CCR
   based on service-specific AVPs used for input to the rating process,
   and possibly on credit-control AVPs received in the AA request.  The
   credit-control server will reserve money from the user's account,
   will rate the request and will send a Credit-Control-Answer message
   to the home Diameter AAA server.  The answer message includes the
   Granted-Service-Unit AVP(s) and MAY include other credit-control-specific
   AVPs, as appropriate.  Additionally, the credit-control
   server MAY set the Validity-Time and MAY include the
   Credit-Control-Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP to
   determine what to do if the sending of credit-control messages to the
   credit-control server has been temporarily prevented.
</t>
<t>
   Upon receiving the Credit-Control-Answer message from the credit-control
   server, the home Diameter AAA server will populate the AA
   answer with the received credit-control AVPs and with the appropriate
   service attributes according to the authorization/authentication-specific
   application (e.g., <xref target="RFC7155"/>, <xref target="RFC4004"/>).  It will then
   forward the packet to the credit-control client.  If the home
   Diameter AAA server receives a credit-control reject message, it will
   simply generate an appropriate authorization reject message to the
   credit-control client, including the credit-control-specific error
   code.
</t>
<t>
   In this model, the credit-control client sends further credit-control
   messages to the credit-control server via the home Diameter AAA
   server.  Upon receiving a successful authorization answer message
   with the Granted-Service-Unit AVP(s), the credit-control client will
   grant the service to the end user and will generate an intermediate
   credit-control request, as required by using credit-control commands.
   The CC-Request-Number of the first UPDATE_REQUEST MUST be set to 1
   (for how to produce unique value for the CC-Request-Number AVP, see
   <xref target="sec-8.2"/>).
</t>
<t>
   If service-specific re-authorization is performed (i.e.,
   authorization-lifetime expires), the credit-control client MUST add
   to the service-specific re-authorization request the Credit-Control
   AVP with a value set to RE_AUTHORIZATION to indicate that the
   credit-control server MUST NOT be contacted.  When session based
   credit-control is used for the subscriber, a constant credit-control
   message stream flows through the home Diameter AAA server.  The home
   Diameter AAA server can make use of this credit-control message flow
   to deduce that the user's activity is ongoing; therefore, it is
   recommended to set the authorization-lifetime to a reasonably high
   value when credit-control is used for the subscriber.
</t>
<t>
   In this scenario, the home Diameter AAA server MUST advertise support
   for the credit-control application to its peers during the capability
   exchange process.
</t>
<t>
   The following diagram illustrates the use of
   authorization/authentication messages to perform the first
   interrogation.  The parallel accounting stream is not shown in the
   figure.
</t>
<figure title="Protocol example with use of the authorization messages for the first interrogation"
        anchor="first_interrogation_auth">
  <artwork><![CDATA[
                Service Element         Diameter
End User          (CC Client)           AAA Server          CC Server
  | Service Request   | AA Request (CC AVPs)                    |
  |------------------>|------------------->|                    |
  |                   |                    | CCR(Initial, CC AVPs)
  |                   |                    |------------------->|
  |                   |                    |    CCA(Granted-Units)
  |                   |                    |<-------------------|
  |                   | AA Answer(Granted-Units)                |
  | Service Delivery  |<-------------------|                    |
  |<----------------->|                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |                   |                    |                    |
  |                   | CCR(Update,Used-Units)                  |
  |                   |------------------->| CCR(Update,Used-Units)
  |                   |                    |------------------->|
  |                   |                    |  CCA(Granted-Units)|
  |                   |  CCA(Granted-Units)|<-------------------|
  |                   |<-------------------|                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  | End of Service    |                    |                    |
  |------------------>| CCR(Termination,Used-Units)             |
  |                   |------------------->| CCR(Term.,Used-Units)
  |                   |                    |------------------->|
  |                   |                    |                CCA |
  |                   |                CCA |<-------------------|
  |                   |<-------------------|                    |
  ]]></artwork>
</figure>
  </section>
</section>
<section anchor="sec-5.3" title="Intermediate Interrogation">
<t>
   When all the granted service units for one unit type are spent by the
   end user or the Validity-Time is expired, the Diameter credit-control
   client MUST send a new Credit-Control-Request to the credit-control
   server.  In the event that credit-control for multiple services is
   applied in one credit-control session (i.e., units associated to
   Service-Identifier(s) or Rating-Group are granted), a new
   Credit-Control-Request MUST be sent to the credit-control server when the
   credit reservation has been wholly consumed, or upon expiration of
   the Validity-Time.  It is always up to the Diameter credit-control
   client to send a new request well in advance of the expiration of the
   previous request in order to avoid interruption in the service
   element.  Even if the granted service units reserved by the credit-control
   server have not been spent upon expiration of the Validity-Time,
   the Diameter credit-control client MUST send a new
   Credit-Control-Request to the credit-control server.
</t><t>
   There can also be mid-session service events, which might affect the
   rating of the current service events.  In this case, a spontaneous
   updating (a new Credit-Control-Request) SHOULD be sent including
   information related to the service event even if all the granted
   service units have not been spent or the Validity-Time has not
   expired.
</t><t>
   When the used units are reported to the credit-control server, the
   credit-control client will not have any units in its possession
   before new granted units are received from the credit-control server.
   When the new granted units are received, these units apply from the
   point where the measurement of the reported used units stopped.
   Where independent credit-control of multiple services is supported,
   this process may be executed for one or more services, a single
   rating-group, or a pool within the (sub)session.
</t><t>
   The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
   intermediate request message.  The Subscription-Id AVP or
   Subscription-Id-Extension AVP SHOULD be included in the intermediate
   message to identify the end user in the credit-control server.
   The Service-Context-Id AVP indicates the service-specific document
   applicable to the request.
</t><t>
   The Requested-Service-Unit AVP MAY contain the new amount of
   requested service units.  Where the Multiple-Services-Credit-Control
   AVP is used, it MUST contain the Requested-Service-Unit AVP if a new
   quota is requested for the associated service/rating-group.  The
   Used-Service-Unit AVP contains the amount of used service units
   measured from the point when the service became active or, if interim
   interrogations are used during the session, from the point when the
   previous measurement ended.  The same unit types used in the previous
   message SHOULD be used.  If several unit types were included in the
   previous answer message, the used service units for each unit type
   MUST be reported.
</t><t>
   The Event-Timestamp AVP SHOULD be included in the request and
   contains the time of the event that triggered the sending of the new
   Credit-Control-Request.
</t><t>
   The credit-control server MUST deduct the used amount from the end
   user's account.  It MAY rate the new request and make a new credit-reservation
   from the end user's account that covers the cost of the
   requested service event.
</t><t>
   A Credit-Control-Answer message with the CC-Request-Type AVP set to
   the value UPDATE_REQUEST MAY include the Cost-Information AVP
   containing the accumulated cost estimation for the session, without
   taking any credit-reservation into account.
</t><t>
   The Credit-Control-Answer message MAY also include the Final-Unit-Indication
   AVP or the QoS-Final-Unit-Indication AVP to indicate that the answer
   message contains the final units for the service.  After the end user has
   consumed these units, the Diameter credit-control-client MUST behave as
   described in <xref target="sec-5.6"/>.
</t><t>
   There can be several intermediate interrogations within a session.
</t>
</section>
<section anchor="sec-5.4" title="Final Interrogation">
<t>
   When the end user terminates the service session, or when the
   graceful service termination described in <xref target="sec-5.6"/> takes place,
   the Diameter credit-control client MUST send a final Credit-Control-Request
   message to the credit-control server.  The CC-Request-Type
   AVP is set to the value TERMINATION_REQUEST.  The Service-Context-Id
   AVP indicates the service-specific document applicable to the
   request.
</t><t>
   The Event-Timestamp AVP SHOULD be included in the request and
   contains the time when the session was terminated.
</t><t>
   The Used-Service-Unit AVP contains the amount of used service units
   measured from the point when the service became active or, if interim
   interrogations are used during the session, from the point when the
   previous measurement ended.  If several unit types were included in
   the previous answer message, the used service units for each unit
   type MUST be reported.
</t><t>
   After final interrogation, the credit-control server MUST refund the
   reserved credit amount not used to the end user's account and deduct
   the used monetary amount from the end user's account.
</t><t>
   A Credit-Control-Answer message with the CC-Request-Type set to the
   value TERMINATION_REQUEST MAY include the Cost-Information AVP
   containing the estimated total cost for the session in question.
</t><t>
   If the user logs off during an ongoing credit-control session, or if
   some other reason causes the user to become logged off (e.g., final-unit
   indication causes user logoff according to local policy), the
   service element, according to application-specific policy, may send a
   Session-Termination-Request (STR) to the home Diameter AAA server as
  usual <xref target="RFC6733"/>.  <xref target="disconnect"/> illustrates the case when the final-unit
   indication causes user logoff upon consumption of the final granted
   units and the generation of STR.
</t>
<figure title="User disconnected due to exhausted account" anchor="disconnect">
  <artwork><![CDATA[
               Service Element        AAA Server        CC Server
End User         (CC Client)
  | Service Delivery  |                    |                    |
  |<----------------->|                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |                   |                    |                    |
  |                   | CCR(Update,Used-Units)                  |
  |                   |------------------->| CCR(Update,Used-Units)
  |                   |                    |------------------->|
  |                   |                  CCA(Final-Unit, Terminate)
  |              CCA(Final-Unit, Terminate)|<-------------------|
  |                   |<-------------------|                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |  Disconnect user  |                    |                    |
  |<------------------| CCR(Termination,Used-Units)             |
  |                   |------------------->| CCR(Term.,Used-Units)
  |                   |                    |------------------->|
  |                   |                    |                CCA |
  |                   |                CCA |<-------------------|
  |                   |<-------------------|                    |
  |                   | STR                |                    |
  |                   |------------------->|                    |
  |                   |               STA  |                    |
  |                   |<-------------------|                    |
  ]]></artwork>
</figure>
</section>
<section anchor="sec-5.5" title="Server-Initiated Credit Re-Authorization">
<t>
   The Diameter credit-control application supports server-initiated
   re-authorization.  The credit-control server MAY optionally initiate
   the credit re-authorization by issuing a Re-Auth-Request (RAR) as
   defined in the Diameter base protocol <xref target="RFC6733"/>.  The
   Auth-Application-Id in the RAR message is set to 4 to indicate Diameter
   Credit Control, and the Re-Auth-Request-Type is set to
   AUTHORIZE_ONLY.
</t><t>
   <xref target="sec-5.1.2"/> defines the feature to enable credit-control for
   multiple services within a single (sub-)session where the server can
   authorize credit usage at a different level of granularity.  Further,
   the server may provide credit resources to multiple services or
   rating groups as a pool (see <xref target="sec-5.1.2"/> for details and
   definitions).  Therefore, the server, based on its service logic and
   its knowledge of the ongoing session, can decide to request credit
   re-authorization for a whole (sub-)session, a single credit pool, a
   single service, or a single rating-group.  To request credit
   re-authorization for a credit pool, the server includes in the RAR
   message the G-S-U-Pool-Identifier AVP indicating the affected pool.
   To request credit re-authorization for a service or a rating-group,
   the server includes in the RAR message the Service-Identifier AVP or
   the Rating-Group AVP, respectively.  To request credit re-authorization
   for all the ongoing services within the (sub-)session,
   the server includes none of the above mentioned AVPs in the RAR
   message.
</t><t>
   If a credit re-authorization is not already ongoing (i.e., the
   credit-control session is in Open state), a credit-control client
   that receives an RAR message with Session-Id equal to a currently
   active credit-control session MUST acknowledge the request by sending
   the Re-Auth-Answer (RAA) message and MUST initiate the credit
   re-authorization toward the server by sending a Credit-Control-Request
   message with the CC-Request-Type AVP set to the value UPDATE_REQUEST.
   The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the
   RAA message to indicate that an additional message (i.e., CCR message
   with the value UPDATE_REQUEST) is required to complete the procedure.
   If a quota was allocated to the service, the credit-control client
   MUST report the used quota in the Credit-Control-Request.  Note that
   the end user does not need to be prompted for the credit re-authorization,
   since the credit re-authorization is transparent to
   the user (i.e., it takes place exclusively between the credit-control
   client and the credit-control server).
</t><t>
   Where multiple services in a user's session are supported, the
   procedure in the above paragraph will be executed at the granularity
   requested by the server in the RAR message.
</t><t>
   If credit re-authorization is ongoing at the time when the RAR
   message is received (i.e., RAR-CCR collision), the credit-control
   client successfully acknowledges the request but does not initiate a
   new credit re-authorization.  The Result-Code 2001 (DIAMETER_SUCCESS)
   SHOULD be used in the RAA message to indicate that a credit re-authorization
   procedure is already ongoing (i.e., the client was in
   PendingU state when the RAR was received).  The credit-control server
   SHOULD process the Credit-Control-Request as if it was received in
   answer to the server initiated credit re-authorization, and should
   consider the server initiated credit re-authorization process
   successful upon reception of the Re-Auth-Answer message.
</t><t>
   When multiple services are supported in a user's session, the server
   may request credit re-authorization for a credit pool (or for the
   (sub-)session) while a credit re-authorization is already ongoing for
   some of the services or rating-groups.  In this case, the client
   acknowledges the server request with an RAA message and MUST send a
   new Credit-Control-Request message to perform re-authorization for
   the remaining services/rating-groups.  The Result-Code 2002
   (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the RAA message to
   indicate that an additional message (i.e., CCR message with value
   UPDATE_REQUEST) is required to complete the procedure.  The server
   processes the received requests and returns an appropriate answer to
   both requests.
</t><t>
   The above-defined procedures are enabled for each of the possibly
   active Diameter credit-control sub-sessions.  The server MAY request
   re-authorization for an active sub-session by including the CC-Sub-Session-Id
   AVP in the RAR message in addition to the Session-Id AVP.
</t>
</section>
<section anchor="sec-5.6" title="Graceful Service Termination">
<t>
   When the user's account runs out of money, the user may not be
   allowed to compile additional chargeable events.  However, the home
   service provider may offer some services; for instance, access to a
   service portal where it is possible to refill the account, for which
   the user is allowed to benefit for a limited time.  The length of
   this time is usually dependent on the home service provider policy.
</t><t>
   This section defines the optional graceful service termination
   feature that MAY be supported by the credit-control server.
   Credit-control client implementations MUST support the Final-Unit-Indication AVP or
   QoS-Final-Unit-Indication AVP with at least the teardown of the ongoing
   service session once the subscriber has consumed all the final granted units.
</t><t>
   Where independent credit-control of multiple services in a single
   credit-control (sub-)session is supported, it is possible to use the
   graceful service termination for each of the services/rating-groups
   independently.  Naturally, the graceful service termination process
   defined in the following sub-sections will apply to the specific
   service/rating-group as requested by the server.
</t><t>
   In some service environments (e.g., NAS), the graceful service
   termination may be used to redirect the subscriber to a service
   portal for online balance refill or other services offered by the
   home service provider.  In this case, the graceful termination
   process installs a set of packet filters to restrict the user's
   access capability only to/from the specified destinations.  All the
   IP packets not matching the filters will be dropped or, possibly,
   re-directed to the service portal.  The user may also be sent an
   appropriate notification as to why the access has been limited.
   These actions may be communicated explicitly from the server to the
   client or may be configured per-service at the client.  Explicitly
   signaled redirect or restrict instructions always take precedence
   over configured ones.
</t><t>
   It is also possible use the graceful service termination to connect
   the prepaid user to a top-up server that plays an announcement and
   prompts the user to replenish the account.  In this case, the
   credit-control server sends only the address of the top-up server
   where the prepaid user shall be connected after the final granted
   units have been consumed.  An example of this is given
   <xref target="app-a7"/>.
</t><t>
   The credit-control server MAY initiate the graceful service
   termination by including the Final-Unit-Indication AVP or the
   QoS-Final-Unit-Indication AVP in the Credit-Control-Answer to indicate that
   the message contains the final units for the service.
</t><t>
   When the credit-control client receives the Final-Unit-Indication AVP or the
   QoS-Final-Unit-Indication AVP in the answer from the server, its behavior
   depends on the value indicated in the Final-Unit-Action AVP.  The server may
   request the following actions: TERMINATE, REDIRECT, or RESTRICT_ACCESS.
</t><t>
   The following figure illustrates the graceful service termination
   procedure described in the following sub-sections.
   <vspace blankLines="24"/>
</t>
<figure title="Optional graceful service termination procedure" anchor="graceful_termination">
  <artwork><![CDATA[
                                        Diameter
End User        Service Element         AAA Server          CC Server
                (CC Client)
  |  Service Delivery |                    |                    |
  |<----------------->|                    |                    |
  |                   |CCR(Update,Used-Units)                   |
  |                   |------------------->|CCR(Update,Used-Units)
  |         :         |                    |------------------->|
  |         :         |                    |CCA(Final-Unit,Action)
  |         :         |                    |<-------------------|
  |                   |CCA(Final-Unit,Action)                   |
  |                   |<-------------------|                    |
  |                   |                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  | ///////////////   |CCR(Update,Used-Units)                   |
  |/Final Units End/->|------------------->|CCR(Update,Used-Units)
  |/Action and    //  |                    |------------------->|
  |/Restrictions //   |                    |  CCA(Validity-Time)|
  |/Start       //    |  CCA(Validity-Time)|<-------------------|
  | /////////////     |<-------------------|                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
  |                 Replenish Account            +-------+      |
  |<-------------------------------------------->|Account|      |
  |                   |                    |     +-------+      |
  |                   |                    |                RAR |
  |                 + |                RAR |<===================|
  |                 | |<===================|                    |
  |                 | | RAA                |                    |
  |  /////////////  | |===================>| RAA                |
  | /If supported / | | CCR(Update)        |===================>|
  | /by CC Server/  | |===================>| CCR(Update)        |
  | /////////////   | |                    |===================>|
  |                 | |                    |   CCA(Granted-Unit)|
  |                 | |   CCA(Granted-Unit)|<===================|
  |  Restrictions ->+ |<===================|                    |
  |  removed          |                    |                    |
  |         :         |                    |                    |
  |        OR         | CCR(Update)        |                    |
  |   Validity-Time ->|------------------->| CCR(Update)        |
  |   expires         |                    |------------------->|
  |                   |                    |   CCA(Granted-Unit)|
  |                   |   CCA(Granted-Unit)|<-------------------|
  |    Restrictions ->|<-------------------|                    |
  |    removed        |                    |                    |
  ]]></artwork>
</figure>
<t>
   In addition, the credit-control server MAY reply with Final-Unit-Indication
   AVP or QoS-Final-Unit-Indication AVP holding a G-S-U AVP with a zero grant,
   indicating that the service SHOULD be terminated immediately, and no further
   reporting is required. A following figure illustrates a graceful service
   termination procedure that applies immediately after receiving a zero grant.
</t>
<figure title="Optional immediate graceful service termination procedure" anchor="immediate_graceful_termination">
  <artwork><![CDATA[
                                        Diameter
End User        Service Element         AAA Server          CC Server
                (CC Client)
  |  Service Delivery |                    |                    |
  |<----------------->|                    |                    |
  |                   |CCR(Update,Used-Units)                   |
  |                   |------------------->|CCR(Update,Used-Units)
  |         :         |                    |------------------->|
  |         :         |                    |CCA(Final-Unit,Action,
  |         :         |                    |           Zero G-S-U)
  |         :         |                    |<-------------------|
  |                   |CCA(Final-Unit,Action,                   |
  |                   |           Zero G-S-U)                   |
  |                   |<-------------------|                    |
  | ///////////////   |                    |                    |
  |/Action and    //  |                    |                    |
  |/Restrictions //   |                    |                    |
  |/Start       //    |                    |                    |
  | /////////////     |                    |                    |
  |         :         |                    |                    |
  |         :         |                    |                    |
   ]]></artwork>
</figure>
<section anchor="sec-5.6.1" title="Terminate Action">
<t>
   The Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP with
   Final-Unit-Action TERMINATE does not include any other information.  When the
   subscriber has consumed the final granted units, the service element MUST
   terminate the service.  This is the default handling applicable whenever the
   credit-control client receives an unsupported Final-Unit-Action value
   and MUST be supported by all the Diameter credit-control client
   implementations conforming to this specification.  A final Credit-Control-Request
   message to the credit-control server MUST be sent if
   the Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP indicating
   action TERMINATE was present at command level.  The CC-Request-Type AVP in
   the request is set to the value TERMINATION_REQUEST.
</t>
</section>
<section anchor="sec-5.6.2" title="Redirect Action">
<t>
   The Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP with
   Final-Unit-Action REDIRECT indicates to the service element supporting this
   action that, upon consumption of the final granted units, the user MUST be
   re-directed to the address specified in the Redirect-Server AVP or
   Redirect-Server-Extension AVP as follows.
</t><t>
   The credit-control server sends the Redirect-Server AVP or
   Redirect-Server-Extension AVP in the Credit-Control-Answer message.
   In such a case, the service element MUST redirect or connect the user to the
   destination specified in the Redirect-Server AVP or Redirect-Server-Extension
   AVP, if possible.  When the end user is redirected (by using protocols others
   than Diameter) to the specified server or connected to the top-up server,
   an additional authorization (and possibly authentication) may be needed
   before the subscriber can replenish the account; however,
   this is out of the scope of this specification.
</t><t>
   In addition to the Redirect-Server AVP or Redirect-Server-Extension AVP,
   the credit-control server MAY include one or more Restriction-Filter-Rule
   AVPs, one or more Filter-Rule AVPs, or one or more Filter-Id AVPs in the
   Credit-Control-Answer message to enable the user to access other services
   (for example, zero-rated services).  In such a case, the access device
   MUST treat all packets according to the Restriction-Filter-Rule AVPs,
   Filter-Rules AVPs and the rules referred to by the Filter-Id AVP.
   After treatment is applied according to these rules, all traffic that has
   not been dropped or already forwarded MUST be redirected to the destination
   specified in the Redirect-Server AVP or Redirect-Server-Extension AVP.
</t><t>
   An entity other than the credit-control server may provision the
   access device with appropriate IP packet filters to be used in
   conjunction with the Diameter credit-control application.  This case
   is considered in <xref target="sec-5.6.3"/>.
</t><t>
   When the final granted units have been consumed, the credit-control
   client MUST perform an intermediate interrogation.  The purpose of
   this interrogation is to indicate to the credit-control server that
   the specified action started and to report the used units.  The
   credit-control server MUST deduct the used amount from the end user's
   account but MUST NOT make a new credit reservation.  The credit-control
   client, however, may send intermediate interrogations before
   all the final granted units have been consumed for which rating and
   money reservation may be needed; for instance, upon Validity-Time
   expires or upon mid-session service events that affect the rating of
   the current service.  Therefore, the credit-control client MUST NOT
   include any rating related AVP in the request sent once all the final
   granted units have been consumed as an indication to the server that
   the requested final unit action started, rating and money reservation
   are not required (when the Multiple-Services-Credit-Control AVP is
   used, the Service-Identifier or Rating-Group AVPs is included to
   indicate the concerned services).  Naturally, the Credit-Control-Answer
   message does not contain any granted service unit and MUST
   include the Validity-Time AVP to indicate to the credit-control
   client how long the subscriber is allowed to use network resources
   before a new intermediate interrogation is sent to the server.
</t><t>
   At the expiry of Validity-Time, the credit-control client sends a
   Credit-Control-Request (UPDATE_REQUEST) as usual.  This message does
   not include the Used-Service-Unit AVP, as there is no allotted quota
   to report.  The credit-control server processes the request and MUST
   perform the credit reservation.  If during this time the subscriber
   did not replenish his/her account, whether he/she will be
   disconnected or will be granted access to services not controlled by
   a credit-control server for an unlimited time is dependent on the
   home service provider policy (note: the latter option implies that
   the service element should not remove the restriction filters upon
   termination of the credit-control).  The server will return the
   appropriate Result-Code (see <xref target="sec-9.1"/>) in the
   Credit-Control-Answer message in order to implement the policy-defined action.
   Otherwise, new quota will be returned, the service element MUST
   remove all the possible restrictions activated by the graceful
   service termination process and continue the credit-control session
   and service session as usual.
</t><t>
   The credit-control client may not wait until the expiration of the
   Validity-Time and may send a spontaneous update (a new Credit-Control-Request)
   if the service element can determine, for instance,
   that communication between the end user and the top-up server took
   place.  An example of this is given in
   <xref target="app-a8"/> (<xref target="flow8"/>).
</t><t>
   Note that the credit-control server may already have initiated the
   above-described process for the first interrogation.  However, the
   user's account might be empty when this first interrogation is
   performed.  In this case, the subscriber can be offered a chance to
   replenish the account and continue the service.  When the credit-control
   client receives (either at session or service-specific level) a
   Final-Unit-Indication AVP or QoS-Final-Unit-Indication AVP,
   together with Validity-Time AVPs, but without Granted-Service-Unit AVP,
   it immediately starts the graceful service termination without sending 
   any message to the server.  An example of this case is illustrated in <xref target="app-a"/>.
</t>
</section>
<section anchor="sec-5.6.3" title="Restrict Access Action">
<t>
   A Final-Unit-Indication AVP with the Final-Unit-Action RESTRICT_ACCESS
   indicates to the device supporting this action that, upon consumption of
   the final granted units, the user's access MUST be restricted according to
   the IP packet filters given in the Restriction-Filter-Rule AVP(s) or
   according to the IP packet filters identified by the Filter-Id AVP(s). The
   credit-control server SHOULD include either the Restriction-Filter-Rule
   AVP or the Filter-Id AVP in the Final-Unit-Indication group AVP of the
   Credit-Control-Answer message.
</t><t>
   A QoS-Final-Unit-Indication AVP with the Final-Unit-Action RESTRICT_ACCESS
   indicates to the device supporting this action that, upon consumption of
   the final granted units, the actions specified in Filter-Rule AVP(s) MUST
   restrict the traffic according to the classifiers in the Filter-Rule AVP(s).
   If Filter-Id AVP(s) are provided in the Credit-Control-Answer
   message, the credit-control client MUST restrict the traffic according to the
   IP packet filters identified by the Filter-Id AVP(s). The credit-control
   server SHOULD include either the Filter-Rule AVP or the
   Filter-Id AVP in the QoS-Final-Unit-Indication group AVP of the
   Credit-Control-Answer message.
</t><t>
   If both Final-Unit-Indication AVP and QoS-Final-Unit-Indication AVP exist in
   the Credit-Control-Answer message, a credit-control client which supports
   the QoS-Final-Unit-Indication AVP SHOULD follow the directives included in
   the QoS-Final-Unit-Indication AVP and SHOULD ignore the
   Final-Unit-Indication AVP.
</t><t>
   An entity other than the credit-control server may provision the
   access device with appropriate IP packet filters to be used in
   conjunction with the Diameter credit-control application.  Such an
   entity may, for instance, configure the access device with IP flows
   to be passed when the Diameter credit-control application indicates
   RESTRICT_ACCESS or REDIRECT.  The access device passes IP packets
   according to the filter rules that may have been received in the
   Credit-Control-Answer message in addition to those that may have been
   configured by the other entity.  However, when the user's account
   cannot cover the cost of the requested service, the action taken is
   the responsibility of the credit-control server that controls the
   prepaid subscriber.
</t><t>
   If another entity working in conjunction with the Diameter credit-control
   application already provisions the access device with all the
   required filter rules for the end user, the credit-control server
   presumably need not send any additional filter.  Therefore, it is
   RECOMMENDED that credit-control server implementations supporting the
   graceful service termination be configurable for sending the
   Restriction-Filter-Rule AVP, the Filter-Rule AVP, the Filter-Id AVP,
   or none of the above.
</t><t>
   When the final granted units have been consumed, the credit-control
   client MUST perform an intermediate interrogation.  The credit-control
   client and the credit-control server process this
   intermediate interrogation and execute subsequent procedures, as
   specified in the previous section for the REDIRECT action.
</t><t>
   The credit-control server may initiate the graceful service
   termination with action RESTRICT_ACCESS already for the first
   interrogation, as specified in the previous section for the REDIRECT
   action.
</t>
</section>
<section anchor="sec-5.6.4" title="Usage of the Server-Initiated Credit Re-Authorization">
<t>
   Once the subscriber replenishes the account, she presumably expects
   all the restrictions placed by the graceful termination procedure to
   be removed immediately and unlimited service access to be resumed.
   For the best user experience, the credit-control server
   implementation MAY support the server-initiated credit re-authorization
   (see <xref target="sec-5.5"/>).  In such a case, upon the successful
   account top-up, the credit-control server sends the Re-Auth-Request
   (RAR) message to solicit the credit re-authorization.  The credit-control
   client initiates the credit re-authorization by sending the
   Credit-Control-Request message with the CC-Request-Type AVP set to
   the value UPDATE_REQUEST.  The Used-Service-Unit AVP is not included
   in the request, as there is no allotted quota to report.  The
   Requested-Service-Unit AVP MAY be included in the request.  After the
   credit-control client successfully receives the Credit-Control-Answer
   with new Granted-Service-Unit, all the possible restrictions
   activated for the purpose of the graceful service termination MUST be
   removed in the service element.  The credit-control session and the
   service session continue as usual.
</t>
</section>
</section>
<section anchor="sec-5.7" title="Failure Procedures">
<t>
   The Credit-Control-Failure-Handling AVP (CCFH), as described in this
   section, determines the behavior of the credit-control client in
   fault situations.  The CCFH may be received from the Diameter home
   AAA server, from the credit-control server, or may be configured
   locally.  The CCFH value received from the home AAA server overrides
   the locally configured value.  The CCFH value received from the
   credit-control server in the Credit-Control-Answer message always
   overrides any existing value.
</t><t>
   The authorization server MAY include the Accounting-Realtime-Required
   AVP to determine what to do if the sending of accounting records to
   the accounting server has been temporarily prevented, as defined in
   <xref target="RFC6733"/>.  It is RECOMMENDED that the client complement the
   credit-control failure procedures with a backup accounting flow toward
   an accounting server.  By using different combinations of
   Accounting-Realtime-Required and Credit-Control-Failure-Handling
   AVPs, different safety levels can be built.  For example, by choosing
   a Credit-Control-Failure-Handling AVP equal to CONTINUE for the
   credit-control flow and an Accounting-Realtime-Required AVP equal to
   DELIVER_AND_GRANT for the accounting flow, the service can be granted
   to the end user even if the connection to the credit-control server
   is down, as long as the accounting server is able to collect the
   accounting information and information exchange is taking place
   between the accounting server and credit-control server.
</t><t>
   As the credit-control application is based on real-time bi-directional
   communication between the credit-control client and the
   credit-control server, the usage of alternative destinations and the
   buffering of messages may not be sufficient in the event of
   communication failures.  Because the credit-control server has to
   maintain session states, moving the credit-control message stream to
   a backup server requires a complex context transfer solution.
   Whether the credit-control message stream is moved to a backup
   credit-control server during an ongoing credit-control session
   depends on the value of the CC-Session-Failover AVP.  However,
   failover may occur at any point in the path between the credit-control
   client and the credit-control server if a transport failure
   is detected with a peer, as described in <xref target="RFC6733"/>.  As a
   consequence, the credit-control server might receive duplicate
   messages.  These duplicates or out of sequence messages can be
   detected in the credit-control server based on the credit-control
   server session state machine (<xref target="sec-7"/>), Session-Id AVP,
   and CC-Request-Number AVP.
</t><t>
   If a failure occurs during an ongoing credit-control session, the
   credit-control client may move the credit-control message stream to
   an alternative server if the CC-server indicated FAILOVER_SUPPORTED
   in the CC-Session-Failover AVP.  A secondary credit-control server
   name, either received from the home Diameter AAA server or configured
   locally, can be used as an address of the backup server.  If the
   CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED, the credit-control
   message stream MUST NOT be moved to a backup server.
</t><t>
   For new credit-control sessions, failover to an alternative credit-control
   server SHOULD be performed if possible.  For instance, if an
   implementation of the credit-control client can determine primary
   credit-control server unavailability, it can establish the new
   credit-control sessions with a possibly available secondary
   credit-control server.
</t><t>
   The AAA transport profile <xref target="RFC3539"/> defines an application layer
   watchdog algorithm that enables failover from a peer that has failed
   and is controlled by a watchdog timer (Tw) defined in <xref target="RFC3539"/>.
   The recommended default initial value for Tw (Twinit) is 30 seconds.
   Twinit may be set as low as 6 seconds; however, according to
   <xref target="RFC3539"/>, setting too low a value for Twinit is likely to result in
   an increased probability of duplicates, as well as an increase in
   spurious failover and failback attempts.  The Diameter base protocol <xref target="RFC6733"/>
   is common to several different types of Diameter AAA applications
   that may be run in the same service element.  Therefore, tuning the
   timer Twinit to a lower value in order to satisfy the requirements of
   real-time applications, such as the Diameter credit-control
   application, will certainly cause the above mentioned problems.  For
   prepaid services, however, the end user expects an answer from the
   network in a reasonable time.  Thus, the Diameter credit-control
   client will react faster than would the underlying base protocol.
   Therefore this specification defines the Tx timer that is used by the
   credit-control client (as defined in <xref target="sec-13"/>) to supervise the
   communication with the credit-control server.  When the Tx timer
   elapses, the credit-control client takes an action to the end user
   according to the Credit-Control-Failure-Handling AVP.
</t><t>
   When Tx timer expires, the Diameter credit-control client always terminates
   the service if the Credit-Control-Failure-Handling (CCFH) AVP is set
   to the value TERMINATE.  The credit-control session may be moved to
   an alternative server only if a protocol error DIAMETER_TOO_BUSY or
   DIAMETER_UNABLE_TO_DELIVER is received before Tx timer expires.  Therefore,
   the value TERMINATE is not appropriate if proper failover behavior is
   desired.
</t><t>
   If the Credit-Control-Failure-Handling AVP is set to the value
   CONTINUE or RETRY_AND_TERMINATE, the service will be granted to the
   end user when the Tx timer expires.  An answer message with granted
   units may arrive later if the base protocol transport failover
   occurred in the path to the credit-control server.  (The Twinit
   default value is 3 times more than the Tx timeout recommended value.) The
   credit-control client SHOULD grant the service to the end user, start
   monitoring the resource usage, and wait for the possible late answer
   until the timeout of the request (e.g., 120 seconds).  If the request
   fails and the CC-Session-Failover AVP is set to
   FAILOVER_NOT_SUPPORTED, the credit-control client terminates or
   continues the service depending on the value set in the CCFH and MUST
   free all the reserved resources for the credit-control session.  If
   the protocol error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is
   received or the request times out and the CC-Session-Failover AVP is
   set to FAILOVER_SUPPORTED, the credit-control client MAY send the
   request to a backup server, if possible.  If the credit-control
   client receives a successful answer from the backup server, it
   continues the credit-control session with such a server.  If the
   re-transmitted request also fails, the credit-control client terminates
   or continues the service depending on the value set in the CCFH and
   MUST free all the reserved resources for the credit-control session.
</t><t>
   If a communication failure occurs during the graceful service
   termination procedure, the service element SHOULD always terminate
   the ongoing service session.
</t><t>
   If the credit-control server detects a failure during an ongoing
   credit-control session, it will terminate the credit-control session
   and return the reserved units back to the end user's account.
</t><t>
   The supervision session timer Tcc (as defined in <xref target="sec-13"/>) is used
   in the credit-control server to supervise the credit-control session.
</t><t>
   In order to support failover between credit-control servers,
   information transfer about the credit-control session and account
   state SHOULD take place between the primary and the secondary
   credit-control server.  Implementations supporting the credit-control
   session failover MUST also ensure proper detection of duplicate or
   out of sequence messages.  The communication between the servers is
   regarded as an implementation issue and is outside of the scope of
   this specification.
</t>
  </section>
</section>
<section anchor="sec-6" title="One Time Event">
<t>
   The one-time event is used when there is no need to maintain any
   state in the Diameter credit-control server; for example, enquiring
   about the price of the service.  The use of a one-time event implies
   that the user has been authenticated and authorized beforehand.
</t>
<t>
   The one-time event can be used when the credit-control client wants
   to know the cost of the service event or to check the account balance
   without any credit-reservation.  It can also be used for refunding
   service units on the user's account or for direct debiting without
  any credit-reservation.  The one-time event is shown in <xref target="onetimeevent" format="default"/>.
</t>
  <figure title="One time event" anchor="onetimeevent">
  <artwork><![CDATA[
                                       Diameter
End User        Service Element        AAA Server        CC Server
                     (CC Client)
  | Service Request   |                    |                    |
  |------------------>|                    |                    |
  |                   | CCR(Event)         |                    |
  |                   |------------------->| CCR(Event)         |
  |                   |                    |------------------->|
  |                   |                    |  CCA(Granted-Units)|
  |                   |  CCA(Granted-Units)|<-------------------|
  |  Service Delivery |<-------------------|                    |
  |<----------------->|                    |                    |
]]>
    </artwork>
    </figure>
<t>
   In environments such as the 3GPP architecture, the one-time event can
   be sent from the service element directly to the credit-control
   server.
</t>
<section anchor="sec-6.1" title="Service Price Enquiry">
<t>
   The credit-control client may need to know the price of the services
   event.  Services offered by application service providers whose
   prices are not known in the credit-control client might exist.  The
   end user might also want to get an estimation of the price of a
   service event before requesting it.
</t>
<t>
   A Diameter credit-control client requesting the cost information MUST
   set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
   Requested-Action AVP set to PRICE_ENQUIRY, and set the requested
   service event information into the Service-Identifier AVP in the
   Credit-Control-Request message.  Additional service event information
   may be sent as service-specific AVPs or within the Service-Parameter-Info
   AVP.  The Service-Context-Id AVP indicates the service-specific 
   document applicable to the request.
</t>
<t>
   The credit-control server calculates the cost of the requested
   service event, but it does not perform any account balance check or
   credit-reservation from the account.
</t>
<t>
   The estimated cost of the requested service event is returned to the
   credit-control client in the Cost-Information AVP in the
   Credit-Control-Answer message.
</t>
</section>
<section anchor="sec-6.2" title="Balance Check">
<t>
   The Diameter credit-control client may only have to verify that the
   end user's account balance covers the cost of a certain service
   without reserving any units from the account at the time of the
   inquiry.  This method does not guarantee that credit would be left
   when the Diameter credit-control client requests the debiting of the
   account with a separate request.
</t>
<t>
   A Diameter credit-control client requesting the balance check MUST
   set the CC-Request-Type AVP equal to EVENT_REQUEST, include a
   Requested-Action AVP set to CHECK_BALANCE, and include the
   Subscription-Id AVP or Subscription-Id-Extension AVP in order to identify
   the end user in the credit-control server.  The Service-Context-Id AVP
   indicates the service-specific document applicable to the request.
</t>
<t>
   The credit-control server makes the balance check, but it does not
   make any credit-reservation from the account.
</t>
<t>
   The result of balance check (ENOUGH_CREDIT/NO_CREDIT) is returned to
   the credit-control client in the Check-Balance-Result AVP in the
   Credit-Control-Answer message.
</t>
</section>
<section anchor="sec-6.3" title="Direct Debiting">
<t>
   There are certain service events for which service execution is
   always successful in the service environment.  The delay between the
   service invocation and the actual service delivery to the end user
   can be sufficiently long that the use of the session-based credit-control
   would lead to unreasonably long credit-control sessions.  In
   these cases, the Diameter credit-control client can use the one-time
   event scenario for direct debiting.  The Diameter credit-control
   client SHOULD be sure that the requested service event execution
   would be successful when this scenario is used.
</t>
<t>
   In the Credit-Control-Request message, the CC-Request-Type is set to
   the value EVENT_REQUEST and the Requested-Action AVP is set to
   DIRECT_DEBITING.  The Subscription-Id AVP or Subscription-Id-Extension AVP
   SHOULD be included to identify the end user in the credit-control server.
   The Event-Timestamp AVP SHOULD be included in the request and contain the
   time when the service event is requested in the service element.  The
   Service-Context-Id AVP indicates the service-specific document
   applicable to the request.
</t>
<t>
   The Diameter credit-control client MAY include the monetary amount to
   be charged in the Requested-Service-Unit AVP, if it knows the cost of
   the service event.  If the Diameter credit-control client does not
   know the cost of the service event, the Requested-Service-Unit AVP
   MAY contain the number of requested service events.  The Service-Identifier
   AVP always indicates the service concerned.  Additional
   service event information to be rated MAY be sent as service-specific
   AVPs or within the Service-Parameter-Info AVP.
</t>
<t>
   The credit-control server SHOULD rate the service event and deduct
   the corresponding monetary amount from the end user's account.  If
   the type of the Requested-Service-Unit AVP is money, no rating is
   needed, but the corresponding monetary amount is deducted from the
   end user's account.
</t>
<t>
   The credit-control server returns the Granted-Service-Unit AVP in the
   Credit-Control-Answer message to the Diameter credit-control client.
   The Granted-Service-Unit AVP contains the amount of service units
   that the Diameter credit-control client can provide to the end user.
   The type of the Granted-Service-Unit can be time, volume, service-specific,
   or money, depending on the type of service event.
</t>
<t>
   If the credit-control server determines that no credit-control is
   needed for the service, it can include the result code indicating
   that the credit-control is not applicable (e.g., service is free of
   charge).
</t>
<t>
   For informative purposes, the Credit-Control-Answer message MAY also
   include the Cost-Information AVP containing the estimated total cost
   of the requested service.
</t>
</section>
<section anchor="sec-6.4" title="Refund">
<t>
   Some services may refund service units to the end user's account; for
   example, gaming services.
</t>
<t>
   The credit-control client MUST set CC-Request-Type to the value
   EVENT_REQUEST and the Requested-Action AVP to REFUND_ACCOUNT in the
   Credit-Control-Request message.  The Subscription-Id AVP or
   Subscription-Id-Extension AVP SHOULD be included to identify the end user in
   the credit-control server.  The Service-Context-Id AVP indicates the service-specific
   document applicable to the request.
</t>
<t>
   The Diameter credit-control client MAY include the monetary amount to
   be refunded in the Requested-Service-Unit AVP.  The Service-Identifier
   AVP always indicates the concerned service.  If the
   Diameter credit-control client does not know the monetary amount to
   be refunded, in addition to the Service-Identifier AVP it MAY send
   service-specific AVPs or the Service-Parameter-Info AVP containing
   additional service event information to be rated.
</t>
<t>
   For informative purposes, the Credit-Control-Answer message MAY also
   include the Cost-Information AVP containing the estimated monetary
   amount of refunded unit.
</t>
</section>
<section anchor="sec-6.5" title="Failure Procedure">
<t>
   Failover to an alternative credit-control server is allowed for a one
   time event, as the server is not maintaining session states.  For
   instance, if the credit-control client receives a protocol error
   DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY, it can re-send the
   request to an alternative server, if possible.  There MAY be protocol
   transparent Diameter relays and redirect agents or Diameter credit-control
   proxies between the credit-control client and credit-control
   server.  Failover may occur at any point in the path between the
   credit-control client and the credit-control server if a transport
   failure is detected with a peer, as described in <xref target="RFC6733"/>.  Because
   there can be duplicate requests for various reasons, the credit-control
   server is responsible for real time duplicate detection.
   Implementation issues for duplicate detection are discussed in
   <xref target="RFC6733"/>, Appendix C.
</t>
<t>
   When the credit-control client detects a communication failure with
   the credit-control server, its behavior depends on the requested
   action.  The Tx timer (as defined in <xref target="sec-13"/>) is used in the
   credit-control client to supervise the communication with the
   credit-control server.
</t>
<t>
   If the requested action is PRICE_ENQUIRY or CHECK_BALANCE and
   communication failure is detected, the credit-control client SHOULD
   forward the request messages to an alternative credit-control server,
   if possible.  The secondary credit-control server name, if received
   from the home Diameter AAA server, can be used as an address of
   backup server.
</t>
<t>
   If the requested action is DIRECT_DEBITING, the Direct-Debiting-Failure-Handling
   AVP (DDFH) controls the credit-control client's
   behavior.  The DDFH may be received from the home Diameter AAA server
   or may be locally configured.  The credit-control server may also
   send the DDFH in any CCA message to be used for direct debiting
   events compiled thereafter.  The DDFH value received from the home
   Diameter AAA server overrides the locally configured value, and the
   DDFH value received from the credit-control server in a
   Credit-Control-Answer message always overrides any existing value.
</t>
<t>
   If the DDFH is set to TERMINATE_OR_BUFFER, the credit-control client
   SHOULD NOT grant the service if it can determine, eventually after a
   possible re-transmission attempt to an alternative credit-control
   server, from the result code or error code in the answer message that
   units have not been debited.  Otherwise, the credit-control client
   SHOULD grant the service to the end user and store the request in the
   credit-control application level non-volatile storage.  (Note that
   re-sending the request at a later time is not a guarantee that the
   service will be debited, as the user's account may be empty when the
   server successfully processes the request.)  The credit-control
   client MUST mark these request messages as possible duplicates by
   setting the T-flag in the command header as described in <xref target="RFC6733"/>,
   Section 3.
</t>
<t>
   If the Direct-Debiting-Failure-Handling AVP is set to CONTINUE, the
   service SHOULD be granted, even if credit-control messages cannot be
   delivered and messages are not buffered.
</t>
<t>
   If the Tx timer expires, the credit-control client MUST continue the
   service and wait for a possible late answer.  If the request times
   out, the credit-control client re-transmits the request (marked with
   T-flag) to a backup credit-control server, if possible.  If the
   re-transmitted request also times out, or if a temporary error is
   received in answer, the credit-control client buffers the request if
   the value of the Direct-Debiting-Failure-Handling AVP is set to
   TERMINATE_OR_BUFFER.  If a failed answer is received for the
   re-transmitted request, the credit-control client frees all the
   resources reserved for the event message and deletes the request
   regardless of the value of the DDFH.
</t>
<t>
   The Credit-Control-Request with the requested action REFUND_ACCOUNT
   should always be stored in the credit-control application level
   non-volatile storage in case of temporary failure.  The credit-control
   client MUST mark the re-transmitted request message as a possible
   duplicate by setting the T-flag in the command header as described in
   <xref target="RFC6733"/>, Section 3.
</t>
<t>
   For stored requests, the implementation may choose to limit the
   number of re-transmission attempts and to define a re-transmission
   interval.
</t>
<t>
   Note that only one place in the credit-control system SHOULD be
   responsible for duplicate detection.  If there is only one credit-control
   server within the given realm, the credit-control server may
   perform duplicate detection.  If there is more than one credit-control
   server in a given realm, only one entity in the credit-control
   system should be responsible, to ensure that the end user's
   account is not debited or credited multiple times for the same
   service event.
</t>
</section>
</section>
<section anchor="sec-7" title="Credit-Control Application State Machine">
<t>
   This section defines the credit-control application state machine.
</t>
  <t>
   The first four state machines are to be observed by credit-control
   clients.  The first one describes the session-based credit-control
   when the first interrogation is executed as part of the
   authorization/authentication process.  The second describes the
   session-based credit-control when the first interrogation is executed
   after the authorization/authentication process.  The requirements as
   to what state machines have to be supported are discussed in <xref target="sec-5.2"/>.
</t>
<t>
   The third state machine describes the session-based credit-control
   for the intermediate and final interrogations.  The fourth one
   describes the event-based credit-control.  These latter state
   machines are to be observed by all implementations that conform to
   this specification.
</t>
<t>
   The fifth state machine describes the credit-control session from a
   credit-control server perspective.
</t>
<t>
   Any event not listed in the state machines MUST be considered an
   error condition, and a corresponding answer, if applicable, MUST be
   returned to the originator of the message.
</t>
<t>
   In the state table, the event 'Failure to send' means that the
   Diameter credit-control client is unable to communicate with the
   desired destination or, if failover procedure is supported, with a
   possibly defined alternative destination (e.g., the request times out
   and the answer message is not received).  This could be due to the
   peer being down, or due to a physical link failure in the path to or
   from the credit-control server.
</t>
<t>
   The event 'Temporary error' means that the Diameter credit-control
   client received a protocol error notification (DIAMETER_TOO_BUSY,
   DIAMETER_UNABLE_TO_DELIVER, or DIAMETER_LOOP_DETECTED) in the
   Result-Code AVP of the Credit-Control-Answer command.  The above
   protocol error notification may ultimately be received in answer to
   the re-transmitted request to a defined alternative destination, if
   failover is supported.
</t>
<t>
   The event 'Failed answer' means that the Diameter credit-control
   client received non-transient failure (permanent failure)
   notification in the Credit-Control-Answer command.  The above
   permanent failure notification may ultimately be received in answer
   to the re-transmitted request to a defined alternative destination,
   if failover is supported.
</t>
<t>
   The action 'store request' means that a request is stored in the
   credit-control application level non-volatile storage.
</t>
<t>
   The event 'Not successfully processed' means that the credit-control
   server could not process the message; e.g., due to an unknown end
   user, account being empty, or errors defined in <xref target="RFC6733"/>.
</t>
<t>
   The event 'User service terminated' can be triggered by various
   reasons, e.g., normal user termination, network failure, and ASR
   (Abort-Session-Request).  The Termination-Cause AVP contains
   information about the termination reason, as specified in <xref target="RFC6733"/>.
</t>
<t>
   The Tx timer, which is used to control the waiting time in the
   credit-control client in the Pending state, is stopped upon exit of
   the Pending state.  The stopping of the Tx timer is omitted in the
   state machine when the new state is Idle, as moving to Idle state
   implies the clearing of the session and all the variables associated
   to it.
</t>
<t>
   The states PendingI, PendingU, PendingT, PendingE, and PendingB stand
   for pending states to wait for an answer to a credit-control request
   related to Initial, Update, Termination, Event, or Buffered request,
   respectively.
</t>
<t>
   The acronyms CCFH and DDFH stand for Credit-Control-Failure-Handling
   and Direct-Debiting-Failure-Handling, respectively.
</t>
<t>
   In the following state machine table, the failover to a secondary
   server upon 'Temporary error' or 'Failure to send' is not explicitly
   described.  Moving an ongoing credit-control message stream to an
   alternative server is, however, possible if the CC-Session-Failover
   AVP is set to FAILOVER_SUPPORTED, as described in <xref target="sec-5.7"/>.
</t>
<t>
   Re-sending a credit-control event to an alternative server is
   supported as described in <xref target="sec-6.5"/>.
</t>
<t>
</t>
  <texttable anchor="cl_sess_first_i_aa" title="CLIENT, SESSION BASED for the first interrogation with AA request">
    <ttcol align="left">State</ttcol>
    <ttcol align="left">Event</ttcol>
    <ttcol align="left">Action</ttcol>
    <ttcol align="left">New State</ttcol>

    <c>Idle</c>
    <c>Client or device requests access/service</c>
    <c>Send AA request with added CC AVPs, start Tx timer</c>
    <c>PendingI</c>


    <c>PendingI</c>
    <c>Successful AA req. answer received</c>
    <c>Grant service to end user, stop Tx timer</c>
    <c>Open</c>

    <c>PendingI</c>
    <c>Tx timer expired </c>
    <c>Disconnect user/dev</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>Failed AA answer received</c>
    <c>Disconnect user/dev</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>AA answer received with result code equal to CREDIT_CONTROL_NOT_APPLICABLE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>User service terminated</c>
    <c>Queue termination event</c>
    <c>PendingI</c>

    <c>PendingI</c>
    <c>Change in rating condition</c>
    <c>Queue changed rating condition event</c>
    <c>PendingI</c>
  </texttable>
  <t>
  </t>
  <texttable anchor="cl_sess_first_i_ccr" title="CLIENT, SESSION BASED for the first interrogation with CCR">
    <ttcol align="left">State</ttcol>
    <ttcol align="left">Event</ttcol>
    <ttcol align="left">Action</ttcol>
    <ttcol align="left">New State</ttcol>

    <c>Idle</c>
    <c>Client or device requests access/service </c>
    <c>Send CC initial req., start Tx timer</c>
    <c>PendingI</c>

    <c>PendingI</c>
    <c>Successful CC initial answer received</c>
    <c>Stop Tx timer</c>
    <c>Open</c>

    <c>PendingI</c>
    <c>Failure to send, or temporary error and CCFH equal to CONTINUE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>Failure to send, or temporary error and CCFH equal to TERMINATE or to RETRY_AND_TERMINATE</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>Tx timer expired and CCFH equal to TERMINATE </c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>Tx timer expired and CCFH equal to CONTINUE or to RETRY_AND_TERMINATE</c>
    <c>Grant service to end user</c>
    <c>PendingI</c>

    <c>PendingI</c>
    <c>CC initial answer received with result code END_USER_SERVICE_DENIED or USER_UNKNOWN</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>CC initial answer received with result code equal to CREDIT_CONTROL_NOT_APPLICABLE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>Failed CC initial answer received and CCFH equal to CONTINUE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>Failed CC initial answer received and CCFH equal to TERMINATE or to RETRY_AND_TERMINATE</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingI</c>
    <c>User service terminated</c>
    <c>Queue termination event</c>
    <c>PendingI</c>

    <c>PendingI</c>
    <c>Change in rating condition</c>
    <c>Queue changed rating condition event</c>
    <c>PendingI</c>
  </texttable>
<t>
</t>
  <texttable anchor="cl_sess_first_inter_final" title="CLIENT, SESSION BASED for intermediate and final interrogations">
    <ttcol align="left">State</ttcol>
    <ttcol align="left">Event</ttcol>
    <ttcol align="left">Action</ttcol>
    <ttcol align="left">New State</ttcol>

    <c>Open</c>
    <c>Granted unit elapses and no final unit indication received</c>
    <c>Send CC update req., start Tx timer</c>
    <c>PendingU</c>

    <c>Open</c>
    <c>Granted unit elapses and final unit action equal to TERMINATE received</c>
    <c>Terminate  end user's service, send CC termination req.</c>
    <c>PendingT</c>

    <c>Open</c>
    <c>Change in rating condition in queue</c>
    <c>Send CC update req., Start Tx timer</c>
    <c>PendingU</c>

    <c>Open</c>
    <c>Service terminated in queue</c>
    <c>Send CC termination req.</c>
    <c>PendingT</c>

    <c>Open</c>
    <c>Change in rating condition or Validity-Time elapses</c>
    <c>Send CC update req., Start Tx timer</c>
    <c>PendingU</c>

    <c>Open</c>
    <c>User service terminated </c>
    <c>Send CC termination req.</c>
    <c>PendingT</c>

    <c>Open</c>
    <c>RAR received</c>
    <c>Send RAA followed by CC update req., start Tx timer</c>
    <c>PendingU</c>
    <!-- Why is the 'start' in the above column not captilized? -->

    <c>PendingU</c>
    <c>Successful CC update answer received</c>
    <c>Stop Tx timer</c>
    <c>Open</c>

    <c>PendingU</c>
    <c>Failure to send, or temporary error and CCFH equal to CONTINUE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingU</c>
    <c>Failure to send, or temporary error and CCFH equal to TERMINATE or to RETRY_AND_TERMINATE</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingU</c>
    <c>Tx timer expired and CCFH equal to TERMINATE </c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingU</c>
    <c>Tx timer expired and CCFH equal to CONTINUE or to RETRY_AND_TERMINATE</c>
    <c>Grant service to end user</c>
    <c>PendingU</c>


    <c>PendingU</c>
    <c>CC update answer received with result code END_USER_SERVICE_DENIED</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>
    <!-- Why does it say result code instead of result code equal to? -->

    <c>PendingU</c>
    <c>CC update answer received with result code equal to CREDIT_CONTROL_NOT_APPLICABLE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingU</c>
    <c>Failed CC update answer received and CCFH equal to CONTINUE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingU</c>
    <c>Failed CC update answer received and CCFH equal to TERMINATE or to RETRY_AND_TERMINATE</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingU</c>
    <c>User service terminated</c>
    <c>Queue termination event</c>
    <c>PendingU</c>

    <c>PendingU</c>
    <c>Change in rating condition</c>
    <c>Queue changed rating condition event</c>
    <c>PendingU</c>

    <c>PendingU</c>
    <c>RAR received</c>
    <c>Send RAA</c>
    <c>PendingU</c>

    <c>PendingT</c>
    <c>Successful CC termination answer received</c>
    <c></c>
    <c>Idle</c>

    <c>PendingT</c>
    <c>Failure to send, temporary error, or failed answer</c>
    <c></c>
    <c>Idle</c>

    <c>PendingT</c>
    <c>Change in rating condition</c>
    <c></c>
    <c>PendingT</c>
  </texttable>
<t>
</t>
  <texttable anchor="table_client_event" title="CLIENT, EVENT BASED">
    <ttcol align="left">State</ttcol>
    <ttcol align="left">Event</ttcol>
    <ttcol align="left">Action</ttcol>
    <ttcol align="left">New State</ttcol>

    <c>Idle</c>
    <c>Client or device requests a one-time service</c>
    <c>Send CC event req., Start Tx timer</c>
    <c>PendingE</c>

    <c>Idle</c>
    <c>Request in storage</c>
    <c>Send stored request</c>
    <c>PendingB</c>

    <c>PendingE</c>
    <c>Successful CC event answer received</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Failure to send, temporary error, failed CC event answer received, or Tx timer expired; requested action CHECK_BALANCE or PRICE_ENQUIRY</c>
    <c>Indicate service error</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>CC event answer received with result code END_USER_SERVICE_DENIED or USER_UNKNOWN and Tx timer running</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>CC event answer received with result code CREDIT_CONTROL_NOT_APPLICABLE; requested action DIRECT_DEBITING</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Failure to send, temporary error, failed CC event answer received; requested action DIRECT_DEBITING; DDFH equal to CONTINUE</c>
    <c>Grant service to end user</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Failed CC event answer received or temporary error; requested action DIRECT_DEBITING; DDFH equal to TERMINATE_OR_BUFFER and Tx timer running</c>
    <c>Terminate end user's service</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Tx timer expired; requested action DIRECT_DEBITING</c>
    <c>Grant service to end user</c>
    <c>PendingE</c>

    <c>PendingE</c>
    <c>Failure to send; requested action DIRECT_DEBITING; DDFH equal to TERMINATE_OR_BUFFER</c>
    <c>Store request with T-flag</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Temporary error; requested action DIRECT_DEBITING; DDFH equal to TERMINATE_OR_BUFFER; Tx timer expired</c>
    <c>Store request</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Failed answer or answer received with result code END_USER_SERVICE DENIED or USER_UNKNOWN; requested action DIRECT_DEBITING; Tx timer expired</c>
    <c></c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Failed CC event answer received; requested action REFUND_ACCOUNT</c>
    <c>Indicate service error and delete request</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Failure to send or Tx timer expired; requested action REFUND_ACCOUNT</c>
    <c>Store request with T-flag</c>
    <c>Idle</c>

    <c>PendingE</c>
    <c>Temporary error, and requested action REFUND_ACCOUNT</c>
    <c>Store request</c>
    <c>Idle</c>

    <c>PendingB</c>
    <c>Successful CC answer received</c>
    <c>Delete request</c>
    <c>Idle</c>

    <c>PendingB</c>
    <c>Failed CC answer received</c>
    <c>Delete request</c>
    <c>Idle</c>

    <c>PendingB</c>
    <c>Failure to send or temporary error</c>
    <c></c>
    <c>Idle</c>
  </texttable>
<t>
</t>
<texttable anchor="table_server_session_event" title="SERVER, SESSION AND EVENT BASED">
    <ttcol align="left">State</ttcol>
    <ttcol align="left">Event</ttcol>
    <ttcol align="left">Action</ttcol>
    <ttcol align="left">New State</ttcol>

    <c>Idle</c>
    <c>CC initial request received and successfully processed</c>
    <c>Send CC initial answer, reserve units, start Tcc</c>
    <c>Open</c>

    <c>Idle</c>
    <c>CC initial request received but not successfully processed</c>
    <c>Send CC initial answer with Result-Code != SUCCESS</c>
    <c>Idle</c>

    <c>Idle</c>
    <c>CC event request received and successfully processed</c>
    <c>Send CC event answer</c>
    <c>Idle</c>

    <c>Idle</c>
    <c>CC event request received but not successfully processed</c>
    <c>Send CC event answer with Result-Code != SUCCESS</c>
    <c>Idle</c>

    <c>Open</c>
    <c>CC update request received and successfully processed</c>
    <c>Send CC update answer, debit used units, reserve new units, restart Tcc</c>
    <c>Open</c>

    <c>Open</c>
    <c>CC update request received but not successfully processed</c>
    <c>Send CC update answer with Result-Code != SUCCESS, debit used units</c>
    <c>Idle</c>

    <c>Open</c>
    <c>CC termination request received and successfully processed</c>
    <c>Send CC termin. answer, Stop Tcc, debit used units</c>
    <c>Idle</c>

    <c>Open</c>
    <c>CC termination request received but not successfully processed</c>
    <c>Send CC termin. answer with Result-Code != SUCCESS, debit used units</c>
    <c>Idle</c>

    <c>Open</c>
    <c>Session supervision timer Tcc expired</c>
    <c>Release reserved units</c>
    <c>Idle</c>
  </texttable>
</section>
<section anchor="sec-8" title="Credit-Control AVPs">
<t>
   This section defines the credit-control AVPs that are specific to
   Diameter credit-control application and that MAY be included in the
   Diameter credit-control messages.
</t>
<t>
   The AVPs defined in this section MAY also be included in
   authorization commands defined in authorization-specific
   applications, such as <xref target="RFC7155"/> and <xref target="RFC4004"/>, if the first
   interrogation is performed as part of the
   authorization/authentication process, as described in <xref target="sec-5.2"/>.
</t>
<t>
   The Diameter AVP rules are defined in the Diameter Base <xref target="RFC6733"/>,
   Section 4.  These AVP rules are observed in AVPs defined in this
   section.
</t>
<t>
   The following table describes the Diameter AVPs defined in the
   credit-control application, their AVP Code values, types, and possible
   flag values.  The AVP Flag rules are explained in
   the Diameter base <xref target="RFC6733"/>, section 4.1.
</t>

<figure>
<artwork align="left"><![CDATA[
                                         +---------------+
                                         |AVP Flag rules |
                                         |----+-----+----|
                  AVP  Section           |    |     |MUST|
Attribute Name    Code Defined Data Type |MUST| MAY |NOT |
-----------------------------------------|----+-----+----|
CC-Correlation-Id 411  8.1    OctetString|    |  M  |  V |
CC-Input-Octets   412  8.24   Unsigned64 | M  |     |  V |
CC-Money          413  8.22   Grouped    | M  |     |  V |
CC-Output-Octets  414  8.25   Unsigned64 | M  |     |  V |
CC-Request-Number 415  8.2    Unsigned32 | M  |     |  V |
CC-Request-Type   416  8.3    Enumerated | M  |     |  V |
CC-Service-       417  8.26   Unsigned64 | M  |     |  V |
  Specific-Units                         |    |     |    |
CC-Session-       418  8.4    Enumerated | M  |     |  V |
  Failover                               |    |     |    |
CC-Sub-Session-Id 419  8.5    Unsigned64 | M  |     |  V |
CC-Time           420  8.21   Unsigned32 | M  |     |  V |
CC-Total-Octets   421  8.23   Unsigned64 | M  |     |  V |
CC-Unit-Type      454  8.32   Enumerated | M  |     |  V |
Check-Balance-    422  8.6    Enumerated | M  |     |  V |
  Result                                 |    |     |    |
Cost-Information  423  8.7    Grouped    | M  |     |  V |
Cost-Unit         424  8.12   UTF8String | M  |     |  V |
Credit-Control    426  8.13   Enumerated | M  |     |  V |
Credit-Control-   427  8.14   Enumerated | M  |     |  V |
  Failure-Handling                       |    |     |    |
Currency-Code     425  8.11   Unsigned32 | M  |     |  V |
Direct-Debiting-  428  8.15   Enumerated | M  |     |  V |
  Failure-Handling                       |    |     |    |
Exponent          429  8.9    Integer32  | M  |     |  V |
Final-Unit-Action 449  8.35   Enumerated | M  |     |  V |
Final-Unit-       430  8.34   Grouped    | M  |     |  V |
  Indication                             |    |     |    |
QoS-Final-Unit-  TBD17 8.68   Grouped    |    |  M  |  V |
  Indication                             |    |     |    |
Granted-Service-  431  8.17   Grouped    | M  |     |  V |
  Unit                                   |    |     |    |
G-S-U-Pool-       453  8.31   Unsigned32 | M  |     |  V |
  Identifier                             |    |     |    |
G-S-U-Pool-       457  8.30   Grouped    | M  |     |  V |
  Reference                              |    |     |    |
Multiple-Services 456  8.16   Grouped    | M  |     |  V |
 -Credit-Control                         |    |     |    |
Multiple-Services 455  8.40   Enumerated | M  |     |  V |
 -Indicator                              |    |     |    |
Rating-Group      432  8.29   Unsigned32 | M  |     |  V |
Redirect-Address  433  8.38   Enumerated | M  |     |  V |
  -Type                                  |    |     |    |
Redirect-Server   434  8.37   Grouped    | M  |     |  V |
Redirect-Server   435  8.39   UTF8String | M  |     |  V |
  -Address                               |    |     |    |
Redirect-Server  TBD13 8.64   Grouped    |    |  M  |  V |
  -Extension                             |    |     |    |
Redirect-Address TBD14 8.65   Address    |    |  M  |  V |
  -IPAddress                             |    |     |    |
Redirect-Address TBD15 8.66   UTF8String |    |  M  |  V |
  -URL                                   |    |     |    |
Redirect-Address TBD16 8.67   UTF8String |    |  M  |  V |
  -SIP-URI                               |    |     |    |
Requested-Action  436  8.41   Enumerated | M  |     |  V |
Requested-Service 437  8.18   Grouped    | M  |     |  V |
  -Unit                                  |    |     |    |
Restriction       438  8.36   IPFiltrRule| M  |     |  V |
  -Filter-Rule                           |    |     |    |
Service-Context   461  8.42   UTF8String | M  |     |  V |
  -Id                                    |    |     |    |
Service-          439  8.28   Unsigned32 | M  |     |  V |
  Identifier                             |    |     |    |
Service-Parameter 440  8.43   Grouped    |    |  M  |  V |
  -Info                                  |    |     |    |
Service-          441  8.44   Unsigned32 |    |  M  |  V |
  Parameter-Type                         |    |     |    |
Service-          442  8.45   OctetString|    |  M  |  V |
  Parameter-Value                        |    |     |    |
Subscription-Id   443  8.46   Grouped    | M  |     |  V |
Subscription-Id   444  8.48   UTF8String | M  |     |  V |
  -Data                                  |    |     |    |
Subscription-Id   450  8.47   Enumerated | M  |     |  V |
  -Type                                  |    |     |    |
Subscription-Id  TBD7  8.58   Grouped    |    |  M  |  V |
  -Extension                             |    |     |    |
Subscription-Id  TBD8  8.59   UTF8String |    |  M  |  V |
  -E164                                  |    |     |    |
Subscription-Id  TBD9  8.60   UTF8String |    |  M  |  V |
  -IMSI                                  |    |     |    |
Subscription-Id  TBD10 8.61   UTF8String |    |  M  |  V |
  -SIP-URI                               |    |     |    |
Subscription-Id  TBD11 8.62   UTF8String |    |  M  |  V |
  -NAI                                   |    |     |    |
Subscription-Id  TBD12 8.63   UTF8String |    |  M  |  V |
  -Private                               |    |     |    |
Tariff-Change     452  8.27   Enumerated | M  |     |  V |
  -Usage                                 |    |     |    |
Tariff-Time       451  8.20   Time       | M  |     |  V |
  -Change                                |    |     |    |
Unit-Value        445  8.8    Grouped    | M  |     |  V |
Used-Service-Unit 446  8.19   Grouped    | M  |     |  V |
User-Equipment    458  8.49   Grouped    |    |  M  |  V |
  -Info                                  |    |     |    |
User-Equipment    459  8.50   Enumerated |    |  M  |  V |
  -Info-Type                             |    |     |    |
User-Equipment    460  8.51   OctetString|    |  M  |  V |
  -Info-Value                            |    |     |    |
User-Equipment   TBD1  8.52   Grouped    |    |  M  |  V |
  -Info-Extension                        |    |     |    |
User-Equipment   TBD2  8.53   OctetString|    |  M  |  V |
  -Info-IMEISV                           |    |     |    |
User-Equipment   TBD3  8.54   OctetString|    |  M  |  V |
  -Info-MAC                              |    |     |    |
User-Equipment   TBD4  8.55   OctetString|    |  M  |  V |
  -Info-EUI64                            |    |     |    |
User-Equipment   TBD5  8.56   OctetString|    |  M  |  V |
  -Info-ModifiedEUI64                    |    |     |    |
User-Equipment   TBD6  8.57   OctetString|    |  M  |  V |
  -Info-IMEI                             |    |     |    |
Value-Digits      447  8.10   Integer64  | M  |     |  V |
Validity-Time     448  8.33   Unsigned32 | M  |     |  V |
]]></artwork></figure>
<section anchor="sec-8.1" title="CC-Correlation-Id AVP">
<t>
   The CC-Correlation-Id AVP (AVP Code 411) is of type OctetString and
   contains information to correlate credit-control requests generated
   for different components of the service; e.g., transport and service
   level.  The one who allocates the Service-Context-Id (i.e., unique
   identifier of a service-specific document) is also responsible for
   defining the content and encoding of the CC-Correlation-Id AVP.
</t><t>
</t>
</section>
<section anchor="sec-8.2" title="CC-Request-Number AVP">
<t>
   The CC-Request-Number AVP (AVP Code 415) is of type Unsigned32 and
   identifies this request within one session.  As Session-Id AVPs are
   globally unique, the combination of Session-Id and CC-Request-Number
   AVPs is also globally unique and can be used in matching credit-control
   messages with confirmations.  An easy way to produce unique
   numbers is to set the value to 0 for a credit-control request of type
   INITIAL_REQUEST and EVENT_REQUEST and to set the value to 1 for the
   first UPDATE_REQUEST, to 2 for the second, and so on until the value
   for TERMINATION_REQUEST is one more than for the last UPDATE_REQUEST.
</t>
</section>
<section anchor="sec-8.3" title="CC-Request-Type AVP">
<t>
   The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
   contains the reason for sending the credit-control request message.
   It MUST be present in all Credit-Control-Request messages.  The
   following values are defined for the CC-Request-Type AVP 
   (The value of zero is reserved):
</t><t>
   INITIAL_REQUEST                 1
</t><t>
      An Initial request is used to initiate a credit-control session,
      and contains credit-control information that is relevant to the
      initiation.
</t><t>
   UPDATE_REQUEST                  2
</t><t>
      An Update request contains credit-control information for an
      existing credit-control session.  Update credit-control requests
      SHOULD be sent every time a credit-control re-authorization is
      needed at the expiry of the allocated quota or validity time.
      Further, additional service-specific events MAY trigger a
      spontaneous Update request.
</t><t>
   TERMINATION_REQUEST             3
</t><t>
      A Termination request is sent to terminate a credit-control
      session and contains credit-control information relevant to the
      existing session.
</t><t>
   EVENT_REQUEST                   4
</t><t>
      An Event request is used when there is no need to maintain any
      credit-control session state in the credit-control server.  This
      request contains all information relevant to the service, and is
      the only request of the service.  The reason for the Event request
      is further detailed in the Requested-Action AVP.  The Requested-Action
      AVP MUST be included in the Credit-Control-Request message
      when CC-Request-Type is set to EVENT_REQUEST.
</t>
</section>
<section anchor="sec-8.4" title="CC-Session-Failover AVP">
<t>
   The CC-Session-Failover AVP (AVP Code 418) is type of Enumerated and
   contains information as to whether moving the credit-control message
   stream to a backup server during an ongoing credit-control session is
   supported.  In communication failures, the credit-control message
   streams can be moved to an alternative destination if the credit-control
   server supports failover to an alternative server.  The
   secondary credit-control server name, if received from the home
   Diameter AAA server, can be used as an address of the backup server.
   An implementation is not required to support moving a credit-control
   message stream to an alternative server, as this also requires moving
   information related to the credit-control session to backup server.
</t><t>
   The following values are defined for the CC-Session-Failover AVP:
</t><t>
   FAILOVER_NOT_SUPPORTED          0
</t><t>
      When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED,
      the credit-control message stream MUST NOT be moved to an
      alternative destination in the case of communication failure.
      This is the default behavior if the AVP isn't included in the
      reply from the authorization or credit-control server.
</t><t>
   FAILOVER_SUPPORTED              1
</t><t>
      When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
      credit-control message stream SHOULD be moved to an alternative
      destination in the case of communication failure.  Moving the
      credit-control message stream to a backup server MAY require that
      information related to the credit-control session should also be
      forwarded to an alternative server.
</t>
</section>
<section anchor="sec-8.5" title="CC-Sub-Session-Id AVP">
<t>
   The CC-Sub-Session-Id AVP (AVP Code 419) is of type Unsigned64 and
   contains the credit-control sub-session identifier.  The combination
   of the Session-Id and this AVP MUST be unique per sub-session, and
   the value of this AVP MUST be monotonically increased by one for all
   new sub-sessions.  The absence of this AVP implies that no
   sub-sessions are in use.
</t>
</section>
<section anchor="sec-8.6" title="Check-Balance-Result AVP">
<t>
   The Check Balance Result AVP (AVP Code 422) is of type Enumerated and
   contains the result of the balance check.  This AVP is applicable
   only when the Requested-Action AVP indicates CHECK_BALANCE in the
   Credit-Control-Request command.
   The following values are defined for the Check-Balance-Result AVP.
</t><t>
   ENOUGH_CREDIT                   0
</t><t>
      There is enough credit in the account to cover the requested
      service.
</t><t>
   NO_CREDIT                       1
</t><t>
      There isn't enough credit in the account to cover the requested
      service.
</t>
</section>
<section anchor="sec-8.7" title="Cost-Information AVP">
<t>
   The Cost-Information AVP (AVP Code 423) is of type Grouped, and it is
   used to return the cost information of a service, which the credit-control
   client can transfer transparently to the end user.  The
   included Unit-Value AVP contains the cost estimate (always type of
   money) of the service, in the case of price enquiry, or the
   accumulated cost estimation, in the case of credit-control session.
</t><t>
   The Currency-Code specifies in which currency the cost was given.
   The Cost-Unit specifies the unit when the service cost is a cost per
   unit (e.g., cost for the service is $1 per minute).
</t><t>
   When the Requested-Action AVP with value PRICE_ENQUIRY is included in
   the Credit-Control-Request command, the Cost-Information AVP sent in
   the succeeding Credit-Control-Answer command contains the cost
   estimation of the requested service, without any reservation being
   made.
</t><t>
   The Cost-Information AVP included in the Credit-Control-Answer
   command with the CC-Request-Type set to UPDATE_REQUEST contains the
   accumulated cost estimation for the session, without taking any
   credit reservation into account.
</t><t>
   The Cost-Information AVP included in the Credit-Control-Answer
   command with the CC-Request-Type set to EVENT_REQUEST or
   TERMINATION_REQUEST contains the estimated total cost for the
   requested service.
</t><t>
   It is defined as follows (per the grouped-avp-def of
   <xref target="RFC6733"/>):
</t>
    <figure>
        <artwork><![CDATA[
                Cost-Information ::= < AVP Header: 423 >
                                     { Unit-Value }
                                     { Currency-Code }
                                     [ Cost-Unit ]
]]>
        </artwork>
    </figure>
</section>
<section anchor="sec-8.8" title="Unit-Value AVP">
<t>
   Unit-Value AVP is of type Grouped (AVP Code 445) and specifies the
   units as decimal value.  The Unit-Value is a value with an exponent;
   i.e., Unit-Value = Value-Digits AVP * 10^Exponent.  This
   representation avoids unwanted rounding off.  For example, the value
   of 2,3 is represented as Value-Digits = 23 and Exponent = -1.  The
   absence of the exponent part MUST be interpreted as an exponent equal
   to zero.
</t><t>
   It is defined as follows (per the grouped-avp-def of
   <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
                    Unit-Value ::= < AVP Header: 445 >
                                   { Value-Digits }
                                   [ Exponent ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.9" title="Exponent AVP">
<t>
   Exponent AVP is of type Integer32 (AVP Code 429) and contains the
   exponent value to be applied for the Value-Digit AVP within the
   Unit-Value AVP.
</t>
</section>
<section anchor="sec-8.10" title="Value-Digits AVP">
<t>
   The Value-Digits AVP is of type Integer64 (AVP Code 447) and contains
   the significant digits of the number.  If decimal values are needed
   to present the units, the scaling MUST be indicated with the related
   Exponent AVP.  For example, for the monetary amount $ 0.05 the value
   of Value-Digits AVP MUST be set to 5, and the scaling MUST be
   indicated with the Exponent AVP set to -2.
</t>
</section>
<section anchor="sec-8.11" title="Currency-Code AVP">
<t>
   The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and
   contains a currency code that specifies in which currency the values
   of AVPs containing monetary units were given.  It is specified by
   using the numeric values defined in the ISO 4217 standard <xref target="ISO4217"/>.
</t>
</section>
<section anchor="sec-8.12" title="Cost-Unit AVP">
<t>
   The Cost-Unit AVP (AVP Code 424) is of type UTF8String, and it is
   used to display a human readable string to the end user.  It
   specifies the applicable unit to the Cost-Information when the
   service cost is a cost per unit (e.g., cost of the service is $1 per
   minute).  The Cost-Unit can be minutes, hours, days, kilobytes,
   megabytes, etc.
</t>
</section>
<section anchor="sec-8.13" title="Credit-Control AVP">
<t>
   The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
   be included in AA requests when the service element has
   credit-control capabilities.
</t><t>
   CREDIT_AUTHORIZATION            0
</t><t>
      If the home Diameter AAA server determines that the user has
      prepaid subscription, this value indicates that the credit-control
      server MUST be contacted to perform the first interrogation.  The
      value of the Credit-Control AVP MUST always be set to 0 in an AA
      request sent to perform the first interrogation and to initiate a
      new credit-control session.
</t><t>
   RE_AUTHORIZATION                1
</t><t>
      This value indicates to the Diameter AAA server that a credit-control
      session is ongoing for the subscriber and that the
      credit-control server MUST NOT be contacted.  The Credit-Control
      AVP set to the value of 1 is to be used only when the first
      interrogation has been successfully performed and the credit-control
      session is ongoing (i.e., re-authorization triggered by
      Authorization-Lifetime).  This value MUST NOT be used in an AA
      request sent to perform the first interrogation.
</t>
</section>
<section anchor="sec-8.14" title="Credit-Control-Failure-Handling AVP">
<t>
   The Credit-Control-Failure-Handling AVP (AVP Code 427) is of type
   Enumerated.  The credit-control client uses information in this AVP
   to decide what to do if sending credit-control messages to the
   credit-control server has been, for instance, temporarily prevented
   due to a network problem.  Depending on the service logic, the
   credit-control server can order the client to terminate the service
   immediately when there is a reason to believe that the service cannot
   be charged, or to try failover to an alternative server, if possible.
   Then the server could either terminate or grant the service, should
   the alternative connection also fail.
</t><t>
   TERMINATE                       0
</t><t>
      When the Credit-Control-Failure-Handling AVP is set to TERMINATE,
      the service MUST only be granted for as long as there is a
      connection to the credit-control server.  If the credit-control
      client does not receive any Credit-Control-Answer message within
      the Tx timer (as defined in <xref target="sec-13"/>), the credit-control
      request is regarded as failed, and the end user's service session
      is terminated.
</t><t>
      This is the default behavior if the AVP isn't included in the
      reply from the authorization or credit-control server.
</t><t>
   CONTINUE                       1
</t><t>
      When the Credit-Control-Failure-Handling AVP is set to CONTINUE,
      the credit-control client SHOULD re-send the request to an
      alternative server in the case of transport or temporary failures,
      provided that a failover procedure is supported in the credit-control
      server and the credit-control client, and that an
      alternative server is available.  Otherwise, the service SHOULD be
      granted, even if credit-control messages can't be delivered.
</t><t>
   RETRY_AND_TERMINATE            2
</t><t>
      When the Credit-Control-Failure-Handling AVP is set to
      RETRY_AND_TERMINATE, the credit-control client SHOULD re-send the
      request to an alternative server in the case of transport or
      temporary failures, provided that a failover procedure is
      supported in the credit-control server and the credit-control
      client, and that an alternative server is available.  Otherwise,
      the service SHOULD NOT be granted when the credit-control messages
      can't be delivered.
</t>
</section>
<section anchor="sec-8.15" title="Direct-Debiting-Failure-Handling AVP">
<t>
   The Direct-Debiting-Failure-Handling AVP (AVP Code 428) is of type
   Enumerated.  The credit-control client uses information in this AVP
   to decide what to do if sending credit-control messages (Requested-Action
   AVP set to DIRECT_DEBITING) to the credit-control server has
   been, for instance, temporarily prevented due to a network problem.
</t><t>
   TERMINATE_OR_BUFFER             0
</t><t>
      When the Direct-Debiting-Failure-Handling AVP is set to
      TERMINATE_OR_BUFFER, the service MUST be granted for as long as
      there is a connection to the credit-control server.  If the
      credit-control client does not receive any Credit-Control-Answer
      message within the Tx timer (as defined in <xref target="sec-13"/>) the
      credit-control request is regarded as failed.  The client SHOULD
      terminate the service if it can determine from the failed answer
      that units have not been debited.  Otherwise the credit-control
      client SHOULD grant the service, store the request in application
      level non-volatile storage, and try to re-send the request.  These
      requests MUST be marked as possible duplicates by setting the T-flag
      in the command header as described in <xref target="RFC6733"/> section 3.
      This is the default behavior if the AVP isn't included in the
      reply from the authorization server.
</t><t>
   CONTINUE                       1
</t><t>
      When the Direct-Debiting-Failure-Handling AVP is set to CONTINUE,
      the service SHOULD be granted, even if credit-control messages
      can't be delivered, and the request should be deleted.
</t>
</section>
<section anchor="sec-8.16" title="Multiple-Services-Credit-Control AVP">
<t>
   Multiple-Services-Credit-Control AVP (AVP Code 456) is of type
   Grouped and contains the AVPs related to the independent credit-control
   of multiple services feature.  Note that each instance of
   this AVP carries units related to one or more services or related to
   a single rating group.
</t><t>
   The Service-Identifier and the Rating-Group AVPs are used to
   associate the granted units to a given service or rating group.  If
   both the Service-Identifier and the Rating-Group AVPs are included,
   the target of the service units is always the service(s) indicated by
   the value of the Service-Identifier AVP(s).  If only the Rating-Group-Id
   AVP is present, the Multiple-Services-Credit-Control AVP
   relates to all the services that belong to the specified rating
   group.
</t><t>
   The G-S-U-Pool-Reference AVP allows the server to specify a G-S-U-Pool-Identifier
   identifying a credit pool within which the units of
   the specified type are considered pooled.  If a G-S-U-Pool-Reference
   AVP is present, then actual service units of the specified type MUST
   also be present.  For example, if the G-S-U-Pool-Reference AVP
   specifies Unit-Type TIME, then the CC-Time AVP MUST be present.
</t><t>
   The Requested-Service-Unit AVP MAY contain the amount of requested
   service units or the requested monetary value.  It MUST be present in
   the initial interrogation and within the intermediate interrogations
   in which new quota is requested.  If the credit-control client does
   not include the Requested-Service-Unit AVP in a request command,
   because for instance, it has determined that the end-user terminated
   the service, the server MUST debit the used amount from the user's
   account but MUST NOT return a new quota in the corresponding answer.
   The Validity-Time, Result-Code, and Final-Unit-Indication  or
   QoS-Final-Unit-Indication AVPs MAY be present in an answer command as defined
   in <xref target="sec-5.1.2"/> and <xref target="sec-5.6"/>
   for the graceful service termination.
</t><t>
   When both the Tariff-Time-Change and Tariff-Change-Usage AVPs are
   present, the server MUST include two separate instances of the
   Multiple-Services-Credit-Control AVP with the Granted-Service-Unit
   AVP associated to the same service-identifier and/or rating-group.
   Where the two quotas are associated to the same pool or to different
   pools, the credit pooling mechanism defined in <xref target="sec-5.1.2"/> applies.
   The Tariff-Change-Usage AVP MUST NOT be included in request commands
   to report used units before, and after tariff time change the Used-Service-Unit
   AVP MUST be used.
</t><t>
   A server not implementing the independent credit-control of multiple
   services functionality MUST treat the Multiple-Services-Credit-Control
   AVP as an invalid AVP.
</t><t>
   The Multiple-Services-Control AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
 Multiple-Services-Credit-Control ::= < AVP Header: 456 >
                                     [ Granted-Service-Unit ]
                                     [ Requested-Service-Unit ]
                                    *[ Used-Service-Unit ]
                                     [ Tariff-Change-Usage ]
                                    *[ Service-Identifier ]
                                     [ Rating-Group ]
                                    *[ G-S-U-Pool-Reference ]
                                     [ Validity-Time ]
                                     [ Result-Code ]
                                     [ Final-Unit-Indication ]
                                     [ QoS-Final-Unit-Indication ]
                                    *[ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.17" title="Granted-Service-Unit AVP">
<t>
   Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
   contains the amount of units that the Diameter credit-control client
   can provide to the end user until the service must be released or the
   new Credit-Control-Request must be sent.  A client is not required to
   implement all the unit types, and it must treat unknown or
   unsupported unit types in the answer message as an incorrect CCA
   answer.  In this case, the client MUST terminate the credit-control
   session and indicate in the Termination-Cause AVP reason
   DIAMETER_BAD_ANSWER.
</t><t>
   The Granted-Service-Unit AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Granted-Service-Unit ::= < AVP Header: 431 >
                                 [ Tariff-Time-Change ]
                                 [ CC-Time ]
                                 [ CC-Money ]
                                 [ CC-Total-Octets ]
                                 [ CC-Input-Octets ]
                                 [ CC-Output-Octets ]
                                 [ CC-Service-Specific-Units ]
                                *[ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.18" title="Requested-Service-Unit AVP">
<t>
   The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
   contains the amount of requested units specified by the Diameter
   credit-control client.  A server is not required to implement all the
   unit types, and it must treat unknown or unsupported unit types as
   invalid AVPs.
</t><t>
   The Requested-Service-Unit AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Requested-Service-Unit ::= < AVP Header: 437 >
                                 [ CC-Time ]
                                 [ CC-Money ]
                                 [ CC-Total-Octets ]
                                 [ CC-Input-Octets ]
                                 [ CC-Output-Octets ]
                                 [ CC-Service-Specific-Units ]
                                *[ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.19" title="Used-Service-Unit AVP">
<t>
   The Used-Service-Unit AVP is of type Grouped (AVP Code 446) and
   contains the amount of used units measured from the point when the
   service became active or, if interim interrogations are used during
   the session, from the point when the previous measurement ended.
   Note: The values reported in a Used-Service-Unit AVP does not necessarily
   have a relation to the grant provided in a Granted-Service-Unit AVP,
   e.g., the value in this AVP may exceed the value in the grant.
</t><t>
   The Used-Service-Unit AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Used-Service-Unit ::= < AVP Header: 446 >
                            [ Tariff-Change-Usage ]
                            [ CC-Time ]
                            [ CC-Money ]
                            [ CC-Total-Octets ]
                            [ CC-Input-Octets ]
                            [ CC-Output-Octets ]
                            [ CC-Service-Specific-Units ]
                           *[ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.20" title="Tariff-Time-Change AVP">
<t>
   The Tariff-Time-Change AVP (AVP Code 451) is of type Time.  It is
   sent from the server to the client and includes the time in seconds
   since January 1, 1900, 00:00 UTC, when the tariff of the service will
   be changed.
</t><t>
   The tariff change mechanism is optional for the client and server,
   and it is not used for time-based services defined in <xref target="sec-5"/>.  If
   a client does not support the tariff time change mechanism, it MUST
   treat Tariff-Time-Change AVP in the answer message as an incorrect
   CCA answer.  In this case, the client terminates the credit-control
   session and indicates in the Termination-Cause AVP reason
   DIAMETER_BAD_ANSWER.
</t><t>
   Omission of this AVP means that no tariff change is to be reported.
</t>
</section>
<section anchor="sec-8.21" title="CC-Time AVP">
<t>
   The CC-Time AVP (AVP Code 420) is of type Unsigned32 and indicates
   the length of the requested, granted, or used time in seconds.
</t>
</section>
<section anchor="sec-8.22" title="CC-Money AVP">
<t>
   The CC-Money AVP (AVP Code 413) is of type Grouped and specifies the
   monetary amount in the given currency.  The Currency-Code AVP SHOULD
   be included.  It is defined as follows (per the grouped-avp-def of
   <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      CC-Money ::= < AVP Header: 413 >
                   { Unit-Value }
                   [ Currency-Code ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.23" title="CC-Total-Octets AVP">
<t>
   The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64 and
   contains the total number of requested, granted, or used octets
   regardless of the direction (sent or received).
</t>
</section>
<section anchor="sec-8.24" title="CC-Input-Octets AVP">
<t>
   The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64 and
   contains the number of requested, granted, or used octets that can
   be/have been received from the end user.
</t>
</section>
<section anchor="sec-8.25" title="CC-Output-Octets AVP">
<t>
   The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64 and
   contains the number of requested, granted, or used octets that can
   be/have been sent to the end user.
</t>
</section>
<section anchor="sec-8.26" title="CC-Service-Specific-Units AVP">
<t>
   The CC-Service-Specific-Units AVP (AVP Code 417) is of type
   Unsigned64 and specifies the number of service-specific units (e.g.,
   number of events, points) given in a selected service.  The
   service-specific units always refer to the service identified in the
   Service-Identifier AVP (or Rating-Group AVP when the
   Multiple-Services-Credit-Control AVP is used).
</t>
</section>
<section anchor="sec-8.27" title="Tariff-Change-Usage AVP">
<t>
   The Tariff-Change-Usage AVP (AVP Code 452) is of type Enumerated and
   defines whether units are used before or after a tariff change, or
   whether the units straddled a tariff change during the reporting
   period.  Omission of this AVP means that no tariff change has
   occurred.
</t><t>
   In addition, when present in answer messages as part of the
   Multiple-Services-Credit-Control AVP, this AVP defines whether units
   are allocated to be used before or after a tariff change event.
</t><t>
   When the Tariff-Time-Change AVP is present, omission of this AVP in
   answer messages means that the single quota mechanism applies.
</t><t>
   Tariff-Change-Usage can be one of the following:
</t><t>
   UNIT_BEFORE_TARIFF_CHANGE       0
</t><t>
      When present in the Multiple-Services-Credit-Control AVP, this
      value indicates the amount of the units allocated for use before a
      tariff change occurs.
</t><t>
      When present in the Used-Service-Unit AVP, this value indicates
      the amount of resource units used before a tariff change had
      occurred.
</t><t>
   UNIT_AFTER_TARIFF_CHANGE        1
</t><t>
      When present in the Multiple-Services-Credit-Control AVP, this
      value indicates the amount of the units allocated for use after a
      tariff change occurs.
</t><t>
      When present in the Used-Service-Unit AVP, this value indicates
      the amount of resource units used after tariff change had
      occurred.
</t><t>
   UNIT_INDETERMINATE              2
</t><t>
      The used unit contains the amount of units that straddle the
      tariff change (e.g., the metering process reports to the credit-control
      client in blocks of n octets, and one block straddled the
      tariff change).  This value is to be used only in the
      Used-Service-Unit AVP.
</t>
</section>
<section anchor="sec-8.28" title="Service-Identifier AVP">
<t>
   The Service-Identifier AVP is of type Unsigned32 (AVP Code 439) and
   contains the identifier of a service.  The specific service the
   request relates to is uniquely identified by the combination of
   Service-Context-Id and Service-Identifier AVPs.
</t><t>
   A usage example of this AVP is illustrated in <xref target="app-a9"/>.
</t>
</section>
<section anchor="sec-8.29" title="Rating-Group AVP">
<t>
   The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and
   contains the identifier of a rating group.  All the services subject
   to the same rating type are part of the same rating group.  The
   specific rating group the request relates to is uniquely identified
   by the combination of Service-Context-Id and Rating-Group AVPs.
</t><t>
   A usage example of this AVP is illustrated in <xref target="app-a9"/>.
</t>
</section>
<section anchor="sec-8.30" title="G-S-U-Pool-Reference AVP">
<t>
   The G-S-U-Pool-Reference AVP (AVP Code 457) is of type Grouped.  It
   is used in the Credit-Control-Answer message, and associates the
   Granted-Service-Unit AVP within which it appears with a credit pool
   within the session.
</t><t>
   The G-S-U-Pool-Identifier AVP specifies the credit pool from which
   credit is drawn for this unit type.
</t><t>
   The CC-Unit-Type AVP specifies the type of units for which credit is
   pooled.
</t><t>
   The Unit-Value AVP specifies the multiplier, which converts between
   service units of type CC-Unit-Type and abstract service units within
   the credit pool (and thus to service units of any other service or
   rating group associated with the same pool).
</t><t>
   The G-S-U-Pool-Reference AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      G-S-U-Pool-Reference    ::= < AVP Header: 457 >
                                  { G-S-U-Pool-Identifier }
                                  { CC-Unit-Type }
                                  { Unit-Value }
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.31" title="G-S-U-Pool-Identifier AVP">
<t>
   The G-S-U-Pool-Identifier AVP (AVP Code 453) is of type Unsigned32
   and identifies a credit pool within the session.
</t>
</section>
<section anchor="sec-8.32" title="CC-Unit-Type AVP">
<t>
   The CC-Unit-Type AVP (AVP Code 454) is of type Enumerated and
   specifies the type of units considered to be pooled into a credit
   pool.
</t><t>
   The following values are defined for the CC-Unit-Type AVP:
</t>
<figure><artwork><![CDATA[
      TIME                         0
      MONEY                        1
      TOTAL-OCTETS                 2
      INPUT-OCTETS                 3
      OUTPUT-OCTETS                4
      SERVICE-SPECIFIC-UNITS       5
]]></artwork></figure>
</section>
<section anchor="sec-8.33" title="Validity-Time AVP">
<t>
   The Validity-Time AVP is of type Unsigned32 (AVP Code 448).  It is
   sent from the credit-control server to the credit-control client.
   The AVP contains the validity time of the granted service units.  The
   measurement of the Validity-Time is started upon receipt of the
   Credit-Control-Answer Message containing this AVP.  If the granted
   service units have not been consumed within the validity time
   specified in this AVP, the credit-control client MUST send a
   Credit-Control-Request message to the server, with CC-Request-Type set to
   UPDATE_REQUEST.  The value field of the Validity-Time AVP is given in
   seconds.
</t><t>
   The Validity-Time AVP is also used for the graceful service
   termination (see <xref target="sec-5.6"/>) to indicate to the credit-control
   client how long the subscriber is allowed to use network resources
   after the specified action (i.e., REDIRECT or RESTRICT_ACCESS)
   started.  When the Validity-Time elapses, a new intermediate
   interrogation is sent to the server.
</t>
</section>
<section anchor="sec-8.34" title="Final-Unit-Indication AVP">
<t>
   The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
   indicates that the Granted-Service-Unit AVP in the Credit-Control-Answer,
   or in the AA answer, contains the final units for the
   service.  After these units have expired, the Diameter credit-control
   client is responsible for executing the action indicated in the
   Final-Unit-Action AVP (see <xref target="sec-5.6"/>).
</t><t>
   If more than one unit type is received in the Credit-Control-Answer,
   the unit type that first expired SHOULD cause the credit-control
   client to execute the specified action.
</t><t>
   In the first interrogation, the Final-Unit-Indication AVP with
   Final-Unit-Action REDIRECT or RESTRICT_ACCESS can also be present
   with no Granted-Service-Unit AVP in the Credit-Control-Answer or in
   the AA answer.  This indicates to the Diameter credit-control client
   to execute the specified action immediately.  If the home service
   provider policy is to terminate the service, naturally, the server
   SHOULD return the appropriate transient failure (see <xref target="sec-9.1"/>) in
   order to implement the policy-defined action.
</t><t>
   The Final-Unit-Action AVP defines the behavior of the service element
   when the user's account cannot cover the cost of the service and MUST
   always be present if the Final-Unit-Indication AVP is included in a
   command.
</t><t>
   If the Final-Unit-Action AVP is set to TERMINATE, the
   Final-Unit-Indication group MUST NOT contain any other AVPs.
</t><t>
    If the Final-Unit-Action AVP is set to REDIRECT at least one of the
    Redirect-Server and Redirect-Server-Extension AVPs MUST be present.
   The Restriction-Filter-Rule AVP
   or the Filter-Id AVP MAY be present in the Credit-Control-Answer
   message if the user is also allowed to access other services that are
   not accessible through the address given in the Redirect-Server AVP.
</t><t>
   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
   Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
</t><t>
   The Filter-Id AVP is defined in <xref target="RFC7155"/>.  The Filter-Id AVP can be
   used to reference an IP filter list installed in the access device by
   means other than the Diameter credit-control application, e.g.,
   locally configured or configured by another entity.
</t><t>
   If the Final-Unit-Action AVP is set to REDIRECT and the type of
   server is not one of the enumerations in the Redirect-Address-Type AVP, then the
   QoS-Final-Unit-Indication AVP SHOULD be used together with the
   Redirect-Server-Extension AVP instead of the Final-Unit-Indication AVP.
</t><t>
   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS or REDIRECT
   and the classification of the restricted traffic cannot be expressed using
   IPFilterRule, or different actions (e.g., QoS) than just allowing traffic needs
   to be enforced, then the QoS-Final-Unit-Indication AVP SHOULD be
   used instead of the Final-Unit-Indication AVP. However, if the credit-control
   server wants to preserve backward compatibility with credit-control clients
   that support only <xref target="RFC4006"/>, the Final-Unit-Indication AVP
   SHOULD be used together with the Filter-Id AVP.
</t><t>
   The Final-Unit-Indication AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Final-Unit-Indication ::= < AVP Header: 430 >
                                { Final-Unit-Action }
                               *[ Restriction-Filter-Rule ]
                               *[ Filter-Id ]
                                [ Redirect-Server ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.35" title="Final-Unit-Action AVP">
<t>
   The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
   indicates to the credit-control client the action to be taken when
   the user's account cannot cover the service cost.
</t><t>
   The Final-Unit-Action can be one of the following:
</t><t>
   TERMINATE                       0
</t><t>
      The credit-control client MUST terminate the service session.
      This is the default handling, applicable whenever the credit-control
      client receives an unsupported Final-Unit-Action value,
      and it MUST be supported by all the Diameter credit-control client
      implementations conforming to this specification.
</t><t>
   REDIRECT                        1
</t><t>
      The service element MUST redirect the user to the address
      specified in the Redirect-Server-Address AVP or one of the AVPs included
      in the Redirect-Server-Extension AVP.  The redirect action
      is defined in <xref target="sec-5.6.2"/>.
</t><t>
   RESTRICT_ACCESS                 2
</t><t>
      The access device MUST restrict the user access according to the
      filter AVPs contained in the applied grouped AVP: according to
      IP packet filters defined in the Restriction-Filter-Rule AVP,
      according to the packet classifier filters defined in Filter-Rule AVP,
      or according to the packet filters identified by the Filter-Id AVP.
      All the packets not matching any filters MUST be dropped
      (see <xref target="sec-5.6.3"/>).
</t>
</section>
<section anchor="sec-8.36" title="Restriction-Filter-Rule AVP">
<t>
   The Restriction-Filter-Rule AVP (AVP Code 438) is of type
   IPFilterRule and provides filter rules corresponding to services that
   are to remain accessible even if there are no more service units
   granted.  The access device has to configure the specified filter
   rules for the subscriber and MUST drop all the packets not matching
   these filters.  Zero, one, or more such AVPs MAY be present in a
   Credit-Control-Answer message or in an AA answer message.
</t>
</section>
<section anchor="sec-8.37" title="Redirect-Server AVP">
<t>
   The Redirect-Server AVP (AVP Code 434) is of type Grouped and
   contains the address information of the redirect server (e.g., HTTP
   redirect server, SIP Server) with which the end user is to be
   connected when the account cannot cover the service cost.  It MUST be
   present when the Final-Unit-Action AVP is set to REDIRECT.
</t><t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Redirect-Server ::= < AVP Header: 434 >
                          { Redirect-Address-Type }
                          { Redirect-Server-Address }
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.38" title="Redirect-Address-Type AVP">
<t>
   The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated
   and defines the address type of the address given in the
   Redirect-Server-Address AVP.
</t><t>
   The address type can be one of the following:
</t><t>
   IPv4 Address                    0
</t><t>
      The address type is in the form of "dotted-decimal" IPv4 address,
      as defined in <xref target="RFC0791"/>.
</t><t>
   IPv6 Address                    1
</t><t>
      The address type is in the form of IPv6 address, as defined in
      <xref target="RFC4291"/>.  The address MUST conform to the text representation of the address
      according to <xref target="RFC5952"/>.
</t><t>
    Because <xref target="RFC5952"/> is more restrictive than the RFC3513 format required by
    <xref target="RFC4006"/>, some legacy implementations may not be compliant with the new
    requirements. Accordingly, implementations receiving this AVP MAY be
    liberal in the textual IPv6 representations that are accepted without
    raising an error.
</t><t>
   URL                             2
</t><t>
      The address type is in the form of Uniform Resource Locator, as
      defined in <xref target="RFC3986"/>.
</t><t>
   SIP URI                         3
</t><t>
      The address type is in the form of SIP Uniform Resource
      Identifier, as defined in <xref target="RFC3261"/>.
</t>
</section>
<section anchor="sec-8.39" title="Redirect-Server-Address AVP">
<t>
   The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String
   and defines the address of the redirect server (e.g., HTTP redirect
   server, SIP Server) with which the end user is to be connected when
   the account cannot cover the service cost.
</t>
</section>
<section anchor="sec-8.40" title="Multiple-Services-Indicator AVP">
<t>
   The Multiple-Services-Indicator AVP (AVP Code 455) is of type
   Enumerated and indicates whether the Diameter credit-control client
   is capable of handling multiple services independently within a
   (sub-) session.  The absence of this AVP means that independent
   credit-control of multiple services is not supported.
</t><t>
   A server not implementing the independent credit-control of multiple
   services MUST treat the Multiple-Services-Indicator AVP as an invalid
   AVP.
</t><t>
   The following values are defined for the Multiple-Services-Indicator
   AVP:
</t><t>
   MULTIPLE_SERVICES_NOT_SUPPORTED 0
</t><t>
      Client does not support independent credit-control of multiple
      services within a (sub-)session.
</t><t>
   MULTIPLE_SERVICES_SUPPORTED     1
</t><t>
      Client supports independent credit-control of multiple services
      within a (sub-)session.
</t>
</section>
<section anchor="sec-8.41" title="Requested-Action AVP">
<t>
   The Requested-Action AVP (AVP Code 436) is of type Enumerated and
   contains the requested action being sent by Credit-Control-Request
   command where the CC-Request-Type is set to EVENT_REQUEST.  The
   following values are defined for the Requested-Action AVP:
</t><t>
   DIRECT_DEBITING                 0
</t><t>
      This indicates a request to decrease the end user's account
      according to information specified in the Requested-Service-Unit
      AVP and/or Service-Identifier AVP (additional rating information
      may be included in service-specific AVPs or in the
      Service-Parameter-Info AVP).  The Granted-Service-Unit AVP in the
      Credit-Control-Answer command contains the debited units.
</t><t>
   REFUND_ACCOUNT                  1
</t><t>
      This indicates a request to increase the end user's account
      according to information specified in the Requested-Service-Unit
      AVP and/or Service-Identifier AVP (additional rating information
      may be included in service-specific AVPs or in the
      Service-Parameter-Info AVP).  The Granted-Service-Unit AVP in the
      Credit-Control-Answer command contains the refunded units.
</t><t>
   CHECK_BALANCE                   2
</t><t>
      This indicates a balance check request.  In this case, the
      checking of the account balance is done without any credit
      reservation from the account.  The Check-Balance-Result AVP in the
      Credit-Control-Answer command contains the result of the balance
      check.
</t><t>
   PRICE_ENQUIRY                   3
</t><t>
      This indicates a price enquiry request.  In this case, neither
      checking of the account balance nor reservation from the account
      will be done; only the price of the service will be returned in
      the Cost-Information AVP in the Credit-Control-Answer Command.
</t>
</section>
<section anchor="sec-8.42" title="Service-Context-Id AVP">
<t>
   The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and
   contains a unique identifier of the Diameter credit-control service-specific 
   document that applies to the request (as defined in
   <xref target="sec-4.1.2"/>).  This is an identifier allocated by the service provider, by
   the service element manufacturer, or by a standardization body, and
   MUST uniquely identify a given Diameter credit-control service-specific
   document.  The format of the Service-Context-Id is:
</t><t>
   "service-context" "@" "domain"
</t><t>
   service-context = Token
</t><t>
   The Token is an arbitrary string of characters and digits.
</t><t>
   'domain' represents the entity that allocated the Service-Context-Id.
   It can be ietf.org, 3gpp.org, etc., if the identifier is allocated by
   a standardization body, or it can be the FQDN of the service provider
   (e.g., provider.example.com) or of the vendor (e.g.,
   vendor.example.com) if the identifier is allocated by a private
   entity.
</t><t>
   This AVP SHOULD be placed as close to the Diameter header as
   possible.
</t><t>
   Service-specific documents that are for private use only (i.e., to
   one provider's own use, where no interoperability is deemed useful)
   may define private identifiers without need of coordination.
   However, when interoperability is wanted, coordination of the
   identifiers via, for example, publication of an informational RFC is
   RECOMMENDED in order to make Service-Context-Id globally available.
</t>
</section>
<section anchor="sec-8.43" title="Service-Parameter-Info AVP">
<t>
   The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
   contains service-specific information used for price calculation or
   rating.  The Service-Parameter-Type AVP defines the service parameter
   type, and the Service-Parameter-Value AVP contains the parameter
   value.  The actual contents of these AVPs are not within the scope of
   this document and SHOULD be defined in another Diameter application,
   in standards written by other standardization bodies, or in
   service-specific documentation.
</t><t>
   In the case of an unknown service request (e.g., unknown Service-Parameter-Type),
   the corresponding answer message MUST contain the
   error code DIAMETER_RATING_FAILED.  A Credit-Control-Answer message
   with this error MUST contain one or more Failed-AVP AVPs containing
   the Service-Parameter-Info AVPs that caused the failure.
</t><t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Service-Parameter-Info ::= < AVP Header: 440 >
                                 { Service-Parameter-Type }
                                 { Service-Parameter-Value }
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.44" title="Service-Parameter-Type AVP">
<t>
   The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)
   and defines the type of the service event specific parameter (e.g.,
   it can be the end-user location or service name).  The different
   parameters and their types are service-specific, and the meanings of
   these parameters are not defined in this document.  Whoever allocates
   the Service-Context-Id (i.e., unique identifier of a service-specific
   document) is also responsible for assigning Service-Parameter-Type
   values for the service and ensuring their uniqueness within the given
   service.  The Service-Parameter-Value AVP contains the value
   associated with the service parameter type.
</t>
</section>
<section anchor="sec-8.45" title="Service-Parameter-Value AVP">
<t>
   The Service-Parameter-Value AVP is of type OctetString (AVP Code 442)
   and contains the value of the service parameter type.
</t>
</section>
<section anchor="sec-8.46" title="Subscription-Id AVP">
<t>
   The Subscription-Id AVP (AVP Code 443) is used to identify the end
   user's subscription and is of type Grouped.  The Subscription-Id AVP
   includes a Subscription-Id-Data AVP that holds the identifier and a
   Subscription-Id-Type AVP that defines the identifier type.
</t><t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
<artwork><![CDATA[
      Subscription-Id ::= < AVP Header: 443 >
                          { Subscription-Id-Type }
                          { Subscription-Id-Data }
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.47" title="Subscription-Id-Type AVP">
<t>
   The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated,
   and it is used to determine which type of identifier is carried by
   the Subscription-Id AVP.
</t><t>
   This specification defines the following subscription identifiers.
   However, new Subscription-Id-Type values can be assigned by IANA
   as defined in <xref target="sec-12"/>.  A server MUST implement
   all the Subscription-Id-Types required to perform credit
   authorization for the services it supports, including possible future
   values.  Unknown or unsupported Subscription-Id-Types MUST be treated
   according to the 'M' flag rule, as defined in <xref target="RFC6733"/>.
</t><t>
   END_USER_E164                   0
</t><t>
      The identifier is in international E.164 format (e.g., MSISDN),
      according to the ITU-T E.164 numbering plan defined in <xref target="E164"/> and
      <xref target="CE164"/>.
</t><t>
   END_USER_IMSI                   1
</t><t>
      The identifier is in international IMSI format, according to the
      ITU-T E.212 numbering plan as defined in <xref target="E212"/> and <xref target="CE212"/>.
</t><t>
   END_USER_SIP_URI                2
</t><t>
      The identifier is in the form of a SIP URI, as defined in <xref target="RFC3261"/>.
</t><t>
   END_USER_NAI                    3
</t><t>
      The identifier is in the form of a Network Access Identifier, as
      defined in <xref target="RFC7542"/>.
</t><t>
   END_USER_PRIVATE                4
</t><t>
      The Identifier is a credit-control server private identifier.
</t>
</section>
<section anchor="sec-8.48" title="Subscription-Id-Data AVP">
<t>
   The Subscription-Id-Data AVP (AVP Code 444) is used to identify the
   end user and is of type UTF8String.  The Subscription-Id-Type AVP
   defines which type of identifier is used.
</t>
</section>
<section anchor="sec-8.49" title="User-Equipment-Info AVP">
<t>
   The User-Equipment-Info AVP (AVP Code 458) is of type Grouped and
   allows the credit-control client to indicate the identity and
   capability of the terminal the subscriber is using for the connection
   to network.
</t><t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
      <figure>
<artwork><![CDATA[
      User-Equipment-Info ::= < AVP Header: 458 >
                              { User-Equipment-Info-Type }
                              { User-Equipment-Info-Value }
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.50" title="User-Equipment-Info-Type AVP">
<t>
   The User-Equipment-Info-Type AVP is of type Enumerated  (AVP Code
   459) and defines the type of user equipment information contained in
   the User-Equipment-Info-Value AVP.
</t><t>
   This specification defines the following user equipment types.
   However, new User-Equipment-Info-Type values can be assigned by an
   IANA as defined in <xref target="sec-12"/>.
</t><t>
   IMEISV                          0
</t><t>
      The identifier contains the International Mobile Equipment
      Identifier and Software Version in the international IMEISV format
      according to 3GPP TS 23.003 <xref target="TGPPIMEI"/>.
</t><t>
   MAC                             1
</t><t>
      The 48-bit MAC address is formatted as described in section 3.21 of <xref target="RFC3580"/>.
</t><t>
   EUI64                           2
</t><t>
      The 64-bit identifier used to identify the hardware instance of the
      product, as defined in <xref target="EUI64"/>.
</t><t>
   MODIFIED_EUI64                  3
</t><t>
      There are a number of types of terminals that have identifiers
      other than IMEI, IEEE 802 MACs, or EUI-64.  These identifiers can
      be converted to modified EUI-64 format as described in <xref target="RFC4291"/>
      or by using some other methods referred to in the service-specific
      documentation.
</t>
</section>
<section anchor="sec-8.51" title="User-Equipment-Info-Value AVP">
<t>
   The User-Equipment-Info-Value AVP (AVP Code 460) is of type
   OctetString.  The User-Equipment-Info-Type AVP defines which type of
   identifier is used.
</t>
</section>
<section anchor="sec-8.52" title="User-Equipment-Info-Extension AVP">
<t>
   The User-Equipment-Info-Extension AVP (AVP Code TBD1) is of type Grouped and
   allows the credit-control client to indicate the identity and
   capability of the terminal the subscriber is using for the connection
   to network. If the type of the equipment is one of the enumerated types of
   User-Equipment-Info-Type AVP, then the credit-control client SHOULD send the
   information in the User-Equipment-Info AVP, in addition to or instead of the
   User-Equipment-Info-Extension AVP. This is in order to preserve backward
   compatibility with credit-control servers that support only <xref target="RFC4006"/>.
   Exactly one AVP MUST be included inside the User-Equipment-Info-Extension AVP.
</t>
<t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
      <figure>
<artwork><![CDATA[
    User-Equipment-Info-Extension ::= < AVP Header: TBD1 >
                               [ User-Equipment-Info-IMEISV ]
                               [ User-Equipment-Info-MAC ]
                               [ User-Equipment-Info-EUI64 ]
                               [ User-Equipment-Info-ModifiedEUI64 ]
                               [ User-Equipment-Info-IMEI ]
                               [ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.53" title="User-Equipment-Info-IMEISV AVP">
<t>
   The User-Equipment-Info-IMEISV (AVP Code TBD2) is of type
   OctetString. The User-Equipment-Info-IMEISV AVP contains the International
   Mobile Equipment Identifier and Software Version in the international
   IMEISV format according to 3GPP TS 23.003 <xref target="TGPPIMEI"/>.
</t>
</section>
<section anchor="sec-8.54" title="User-Equipment-Info-MAC AVP">
<t>
   The User-Equipment-Info-MAC (AVP Code TBD3) is of type
   OctetString. The User-Equipment-Info-MAC AVP contains the 48-bit MAC
   address is formatted as described in section 4.1.7.8 of <xref target="RFC5777"/>.
</t>
</section>
<section anchor="sec-8.55" title="User-Equipment-Info-EUI64 AVP">
<t>
   The User-Equipment-Info-EUI64 (AVP Code TBD4) is of type
   OctetString. The UUser-Equipment-Info-EUI64 AVP contains the 64-bit
   identifier used to identify the hardware instance of the product,
   as defined in <xref target="EUI64"/>.
</t>
</section>
<section anchor="sec-8.56" title="User-Equipment-Info-ModifiedEUI64 AVP">
<t>
   The User-Equipment-Info-ModifiedEUI64 (AVP Code TBD5) is of type
   OctetString. There are a number of types of terminals that have identifiers
   other than IMEI, IEEE 802 MACs, or EUI-64. These identifiers can be
   converted to modified EUI-64 format as described in <xref target="RFC4291"/>
   or by using some other methods referred to in the service-specific
   documentation. The User-Equipment-Info-ModifiedEUI64 AVP contains such identifiers.
</t>
</section>
<section anchor="sec-8.57" title="User-Equipment-Info-IMEI AVP">
<t>
   The User-Equipment-Info-IMEI (AVP Code TBD6) is of type OctetString.
   The User-Equipment-Info-IMEI AVP contains the International Mobile Equipment
   Identifier in the international IMEI format
   according to 3GPP TS 23.003 <xref target="TGPPIMEI"/>.
</t>
</section>
<section anchor="sec-8.58" title="Subscription-Id-Extension AVP">
<t>
   The Subscription-Id-Extension AVP (AVP Code TBD7) is used to identify the end
   user's subscription and is of type Grouped.  The Subscription-Id-Extension
   group AVP MUST include an AVP holding the subscription identifier.
   The type of this included AVP indicates the type of the subscription
   identifier.
   For each of the enumerated values of the Subscription-Id-Type AVP, there
   is a corresponding sub-AVP for use within the Subscription-Id-Extension group AVP.
   If a new identifier type is required a corresponding new sub-AVP SHOULD be defined
   for use within the Subscription-Id-Extension group AVP.
</t><t>
   If full backward compatibility with <xref target="RFC4006"/> is required, then
   the Subscription-Id AVP MUST be used to indicate identifier types enumerated in
   the Subscription-Id-Type AVP, whereas the Subscription-Id-Extension AVP MUST be
   used only for newly defined identifier types. If full backward compatibility
   with <xref target="RFC4006"/> is not required, then the Subscription-Id-Extension
   AVP MAY be used to carry out the existing identifier types. In this case,
   Subscription-Id-Extension AVP MAY be sent together with Subscription-Id AVP.
</t><t>
   Exactly one sub-AVP MUST be included inside the Subscription-Id-Extension AVP.
</t><t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
<artwork><![CDATA[
      Subscription-Id-Extension ::= < AVP Header: TBD7 >
                          [ Subscription-Id-E164 ]
                          [ Subscription-Id-IMSI ]
                          [ Subscription-Id-SIP-URI ]
                          [ Subscription-Id-NAI ]
                          [ Subscription-Id-Private ]
                          [ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.59" title="Subscription-Id-E164 AVP">
<t>
   The Subscription-Id-E164 (AVP Code TBD8) is of type UTF8String.
   The Subscription-Id-E164 AVP contains the international E.164 format
   (e.g., MSISDN), according to the ITU-T E.164 numbering plan defined in
   <xref target="E164"/> and <xref target="CE164"/>.
</t>
</section>
<section anchor="sec-8.60" title="Subscription-Id-IMSI AVP">
<t>
   The Subscription-Id-IMSI (AVP Code TBD9) is of type UTF8String.
   The Subscription-Id-IMSI AVP contains the international IMSI format,
   according to the ITU-T E.212 numbering plan as defined in
   <xref target="E212"/> and <xref target="CE212"/>.
</t>
</section>
<section anchor="sec-8.61" title="Subscription-Id-SIP-URI AVP">
<t>
   The Subscription-Id-SIP-URI (AVP Code TBD10) is of type UTF8String.
   The Subscription-Id-SIP-URI AVP contains the identifier in the form of a SIP
   URI, as defined in <xref target="RFC3261"/>.
</t>
</section>
<section anchor="sec-8.62" title="Subscription-Id-NAI AVP">
<t>
   The Subscription-Id-NAI (AVP Code TBD11) is of type UTF8String.
   The Subscription-Id-NAI AVP contains the identifier in the form of a
   Network Access Identifier, as defined in <xref target="RFC7542"/>.
</t>
</section>
<section anchor="sec-8.63" title="Subscription-Id-Private AVP">
<t>
   The Subscription-Id-Private (AVP Code TBD12) is of type UTF8String.
   The Subscription-Id-Private AVP contains a credit-control server private
   identifier.
</t>
</section>
<section anchor="sec-8.64" title="Redirect-Server-Extension AVP">
<t>
   The Redirect-Server-Extension AVP (AVP Code TBD13) is of type Grouped and
   contains the address information of the redirect server (e.g., HTTP
   redirect server, SIP Server) with which the end user is to be
   connected when the account cannot cover the service cost.  It MUST be
   present inside the QoS-Final-Unit-Indication AVP when the Final-Unit-Action
   AVP is set to REDIRECT. If the type of the redirect server is one of the
   enumerated values of the Redirect-Address-Type AVP, then the credit-control server
   SHOULD send the information in the Redirect-Server AVP, in addition to or
   instead of the Redirect-Server-Extension AVP. This is in order to preserve
   backward compatibility with credit-control clients that support
   only <xref target="RFC4006"/>.
   Exactly one AVP MUST be included inside the Redirect-Server-Extension AVP.
</t><t>
   It is defined as follows (per the grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      Redirect-Server-Extension ::= < AVP Header: TBD13 >
                          [ Redirect-Address-IPAddress ]
                          [ Redirect-Address-URL ]
                          [ Redirect-Address-SIP-URI ]
                          [ AVP ]
]]>
        </artwork>
      </figure>
</section>
<section anchor="sec-8.65" title="Redirect-Address-IPAddress AVP">
<t>
   The Redirect-Address-IPAddress AVP (AVP Code TBD14) is of type Address
   and defines the IPv4 or IPv6 address of the redirect server with which the end user is to
   be connected when the account cannot cover the service cost.
</t>
<t>
   When encoded as an IPv6 address in 16 bytes, the IPv4-mapped IPv6
   format <xref target="RFC4291"/> MAY be used to indicate an IPv4 address.
</t>
<t>The interpretation of Redirect-Address-IPAddress by the Diameter
    Credit-control Client is a matter of local policy.</t>
</section>
<section anchor="sec-8.66" title="Redirect-Address-URL AVP">
<t>
   The Redirect-Address-URL AVP (AVP Code TBD15) is of type UTF8String
   and defines the address of the redirect server with which the end user is to
   be connected when the account cannot cover the service cost. The address
   type is in the form of Uniform Resource Locator,
   as defined in <xref target="RFC3986"/>.  Note that individual URL schemes may restrict the
   contents of the UTF8String.
</t>
</section>
<section anchor="sec-8.67" title="Redirect-Address-SIP-URI AVP">
<t>
   The Redirect-Address-SIP-URI AVP (AVP Code TBD16) is of type UTF8String
   and defines the address of the redirect server with which the end user is to
   be connected when the account cannot cover the service cost. The address
   type is in the form of SIP Uniform Resource Identifier,
   as defined in <xref target="RFC3261"/>.
</t>
</section>
<section anchor="sec-8.68" title="QoS-Final-Unit-Indication AVP">
<t>
   The QoS-Final-Unit-Indication AVP (AVP Code TBD17) is of type Grouped and
   indicates that the Granted-Service-Unit AVP in the Credit-Control-Answer,
   or in the AA answer, contains the final units for the
   service.  After these units have expired, the Diameter credit-control
   client is responsible for executing the action indicated in the
   Final-Unit-Action AVP (see <xref target="sec-5.6"/>).
</t><t>
   If more than one unit type is received in the Credit-Control-Answer,
   the unit type that first expired SHOULD cause the credit-control
   client to execute the specified action.
</t><t>
   In the first interrogation, the QoS-Final-Unit-Indication AVP with
   Final-Unit-Action REDIRECT or RESTRICT_ACCESS can also be present
   with no Granted-Service-Unit AVP in the Credit-Control-Answer or in
   the AA answer.  This indicates to the Diameter credit-control client
   to execute the specified action immediately.  If the home service
   provider policy is to terminate the service, naturally, the server
   SHOULD return the appropriate transient failure (see <xref target="sec-9.1"/>) in
   order to implement the policy-defined action.
</t><t>
   The Final-Unit-Action AVP defines the behavior of the service element
   when the user's account cannot cover the cost of the service and MUST
   always be present if the QoS-Final-Unit-Indication AVP is included in a
   command.
</t><t>
   If the Final-Unit-Action AVP is set to TERMINATE, the
   QoS-Final-Unit-Indication group MUST NOT contain any other AVPs.
</t><t>
   If the Final-Unit-Action AVP is set to REDIRECT then the 
   Redirect-Server-Extension AVPs MUST be present.
   The Filter-Rule AVP or the Filter-Id AVP MAY be present in the
   Credit-Control-Answer message if the user is also allowed to access other
   services that are not accessible through the address given in the
   Redirect-Server-Extension AVP or if the access to these services needs to be
   limited in some way (e.g., QoS).
</t><t>
   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
   Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
</t><t>
   The Filter-Rule AVP is defined in <xref target="RFC5777"/>.  The Filter-Rule
   AVP can be used to define a specific condition and action combination. If
   used only with traffic conditions, it should define which traffic should
   allowed when no more service units are granted. However, if QoS or treatment
   information exists in the AVP, these actions should be executed, e.g.,
   limiting the allowed traffic with certain QoS. When multiple Filter-Rule AVPs
   exist, precedence should be determined as defined in <xref target="RFC5777"/>.
</t><t>
   The Filter-Id AVP is defined in <xref target="RFC7155"/>.  The Filter-Id AVP can be
   used to reference an IP filter list installed in the access device by
   means other than the Diameter credit-control application, e.g.,
   locally configured or configured by another entity.
</t><t>
   If the Final-Unit-Action AVP is set to TERMINATE, or set to
   RESTRICT_ACCESS and the action required is allow only traffic that could be
   classified using an IPFilterRule, or set to REDIRECT of a type which is one
   of the types in the Redirect-Address-Type AVP, then the credit-control server
   SHOULD send the information in the Final-Unit-Indication AVP, in addition to
   or instead of the QoS-Final-Unit-Indication AVP. This is in order to preserve
   backward compatibility with credit-control clients that support
   only <xref target="RFC4006"/>.
</t><t>
   The QoS-Final-Unit-Indication AVP is defined as follows (per the
   grouped-avp-def of <xref target="RFC6733"/>):
</t>
<figure>
        <artwork><![CDATA[
      QoS-Final-Unit-Indication ::= < AVP Header: TBD17 >
                                { Final-Unit-Action }
                               *[ Filter-Rule ]
                               *[ Filter-Id ]
                                [ Redirect-Server-Extension ]
                               *[ AVP ]
]]>
        </artwork>
      </figure>
</section>
</section>
<section anchor="sec-9" title="Result Code AVP Values">
<t>
   This section defines new Result-Code AVP <xref target="RFC6733"/> values that must
   be supported by all Diameter implementations that conform to this
   specification.
</t><t>
   The Credit-Control-Answer message includes the Result-Code AVP, which
   may indicate that an error was present in the Credit-Control-Request
   message.  A rejected Credit-Control-Request message SHOULD cause the
   user's session to be terminated.
</t>
<section anchor="sec-9.1" title="Transient Failures">
<t>
   Errors that fall within the transient failures category are used to
   inform a peer that the request could not be satisfied at the time it
   was received, but that the request MAY be able to be satisfied in the
   future.
</t><t>
   DIAMETER_END_USER_SERVICE_DENIED           4010
</t><t>
      The credit-control server denies the service request due to
      service restrictions.  If the CCR contained used-service-units,
      they are deducted, if possible.
</t><t>
   DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE     4011
</t><t>
      The credit-control server determines that the service can be
      granted to the end user but that no further credit-control is
      needed for the service (e.g., service is free of charge).
</t><t>
   DIAMETER_CREDIT_LIMIT_REACHED              4012
</t><t>
      The credit-control server denies the service request because the
      end user's account could not cover the requested service.  If the
      CCR contained used-service-units they are deducted, if possible.
</t>
</section>
<section anchor="sec-9.2" title="Permanent Failures">
<t>
   Errors that fall within the permanent failure category are used to
   inform the peer that the request failed and should not be attempted
   again.
</t><t>
   DIAMETER_USER_UNKNOWN                      5030
</t><t>
      The specified end user is unknown in the credit-control server.
</t><t>
   DIAMETER_RATING_FAILED                     5031
</t><t>
      This error code is used to inform the credit-control client that
      the credit-control server cannot rate the service request due to
      insufficient rating input, an incorrect AVP combination, or an AVP
      or an AVP value that is not recognized or supported in the rating.
      The Failed-AVP AVP MUST be included and contain a copy of the
      entire AVP(s) that could not be processed successfully or an
      example of the missing AVP complete with the Vendor-Id if
      applicable.  The value field of the missing AVP should be of
      correct minimum length and contain zeros.
</t>
</section>
</section>
<section anchor="sec-10" title="AVP Occurrence Table">
<t>
   The following table presents the AVPs defined in this document and
   specifies in which Diameter messages they MAY or MUST NOT be present.
   Note that AVPs that can only be present within a Grouped AVP are not
   represented in this table.
</t><t>
   The table uses the following symbols:
</t>
<figure><artwork><![CDATA[
      0     The AVP MUST NOT be present in the message.
      0+    Zero or more instances of the AVP MAY be present in the
            message.
      0-1   Zero or one instance of the AVP MAY be present in the
            message.  It is considered an error if there is more
            than one instance of the AVP.
      1     One instance of the AVP MUST be present in the message.
      1+    At least one instance of the AVP MUST be present in the
            message.
]]></artwork></figure>
<section anchor="sec-10.1" title="Credit-Control AVP Table">
<t>
   The table in this section is used to represent which credit-control
   application-specific AVPs defined in this document are to be present
   in the credit-control messages.
</t>
<figure><artwork align="left"><![CDATA[
                                       +-----------+
                                       |  Command  |
                                       |   Code    |
                                       |-----+-----+
         Attribute Name                | CCR | CCA |
         ------------------------------|-----+-----+
         Acct-Multi-Session-Id         | 0-1 | 0-1 |
         Auth-Application-Id           | 1   | 1   |
         CC-Correlation-Id             | 0-1 | 0   |
         CC-Session-Failover           | 0   | 0-1 |
         CC-Request-Number             | 1   | 1   |
         CC-Request-Type               | 1   | 1   |
         CC-Sub-Session-Id             | 0-1 | 0-1 |
         Check-Balance-Result          | 0   | 0-1 |
         Cost-Information              | 0   | 0-1 |
         Credit-Control-Failure-       | 0   | 0-1 |
            Handling                   |     |     |
         Destination-Host              | 0-1 | 0   |
         Destination-Realm             | 1   | 0   |
         Direct-Debiting-Failure-      | 0   | 0-1 |
            Handling                   |     |     |
         Event-Timestamp               | 0-1 | 0-1 |
         Failed-AVP                    | 0   | 0+  |
         Final-Unit-Indication         | 0   | 0-1 |
         QoS-Final-Unit-Indication     | 0   | 0-1 |
         Granted-Service-Unit          | 0   | 0-1 |
         Multiple-Services-Credit-     | 0+  | 0+  |
            Control                    |     |     |
         Multiple-Services-Indicator   | 0-1 | 0   |
         Origin-Host                   | 1   | 1   |
         Origin-Realm                  | 1   | 1   |
         Origin-State-Id               | 0-1 | 0-1 |
         Proxy-Info                    | 0+  | 0+  |
         Redirect-Host                 | 0   | 0+  |
         Redirect-Host-Usage           | 0   | 0-1 |
         Redirect-Max-Cache-Time       | 0   | 0-1 |
         Requested-Action              | 0-1 | 0   |
         Requested-Service-Unit        | 0-1 | 0   |
         Route-Record                  | 0+  | 0+  |
         Result-Code                   | 0   | 1   |
         Service-Context-Id            | 1   | 0   |
         Service-Identifier            | 0-1 | 0   |
         Service-Parameter-Info        | 0+  | 0   |
         Session-Id                    | 1   | 1   |
         Subscription-Id               | 0+  | 0   |
         Subscription-Id-Extension     | 0+  | 0   |
         Termination-Cause             | 0-1 | 0   |
         User-Equipment-Info           | 0-1 | 0   |
         User-Equipment-Info-Extension | 0-1 | 0   |
         Used-Service-Unit             | 0+  | 0   |
         User-Name                     | 0-1 | 0-1 |
         Validity-Time                 | 0   | 0-1 |
         ------------------------------|-----+-----+
]]></artwork></figure>
</section>
<section anchor="sec-10.2" title="Re-Auth-Request/Answer AVP Table">
<t>
   This section defines AVPs that are specific to the Diameter credit-control
   application and that MAY be included in the Diameter
   Re-Auth-Request/Answer (RAR/RAA) message <xref target="RFC6733"/>.
</t><t>
   Re-Auth-Request/Answer command MAY include the following additional
   AVPs:
</t>
<figure>
<artwork align="left"><![CDATA[
                                       +---------------+
                                       | Command Code  |
                                       |-------+-------+
         Attribute Name                |  RAR  |  RAA  |
         ------------------------------+-------+-------+
         CC-Sub-Session-Id             |  0-1  |  0-1  |
         G-S-U-Pool-Identifier         |  0-1  |  0-1  |
         Service-Identifier            |  0-1  |  0-1  |
         Rating-Group                  |  0-1  |  0-1  |
         ------------------------------+-------+-------+
]]></artwork>
</figure>
</section>
</section>
<section anchor="sec-11" title="RADIUS/Diameter Credit-Control Interworking Model">
<t>
   This section defines the basic principles for the Diameter credit-control/RADIUS
   prepaid inter-working model; that is, a message
   translation between a RADIUS based prepaid solution and a Diameter
   credit-control application.  A complete description of the protocol
   translations between RADIUS and the Diameter credit-control
   application is beyond the scope of this specification and SHOULD be
   addressed in another appropriate document, such as the RADIUS prepaid
   specification.
</t><t>
   The Diameter credit-control architecture may have a Translation Agent
   capable of translation between RADIUS prepaid and Diameter credit-control
   protocols.  An AAA server (usually the home AAA server) may
   act as a Translation Agent and as a Diameter credit-control client
   for service elements that use credit-control mechanisms other than
   Diameter credit-control for instance, RADIUS prepaid.  In this case,
   the home AAA server contacts the Diameter credit-control server as
   part of the authorization process.  The interworking architecture is
   illustrated <xref target="se_with_translation" format="default"/>, and interworking flow in <xref target="diam_rad_prepaid_flow" format="default"/>.  In a
   roaming situation the service element (e.g., the NAS) may be located
   in the visited network, and a visited AAA server is usually
   contacted.  The visited AAA server connects then to the home AAA
   server.
</t>
<figure title="Credit-control architecture with service element
                  containing translation agent, translating RADIUS
                  prepaid to Diameter credit-control protocol"
        anchor="se_with_translation">
<artwork><![CDATA[
                               RADIUS Prepaid
+--------+       +---------+   protocol +------------+  +--------+
|  End   |<----->| Service |<---------->| Home AAA   |  |Business|
|  User  |       | Element |            |  Server    |  |Support |
+--------+   +-->|         |            |+----------+|->|System  |
             |   +---------+            ||CC Client ||  |        |
             |                          |+----------+|  |        |
+--------+   |                          +------^-----+  +----^---+
|  End   |<--+                Credit-Control   |             |
|  User  |                          Protocol   |             |
+--------+                             +-------V--------+    |
                                       |Credit-Control  |----+
                                       |   Server       |
                                       +----------------+
]]></artwork></figure>
<t>
   When the AAA server acting as a Translation Agent receives an initial
   RADIUS Access-Request message from service element (e.g., NAS
   access), it performs regular authentication and authorization.  If
   the RADIUS Access-Request message indicates that the service element
   is capable of credit-control, and if the home AAA server finds that
   the subscriber is a prepaid subscriber, then a Diameter credit-control
   request SHOULD be sent toward the credit-control server to
   perform credit authorization and to establish a credit-control
   session.  After the Diameter credit-control server checks the end
   user's account balance, rates the service, and reserves credit from
   the end user's account, the reserved quota is returned to the home
   AAA server in the Diameter Credit-Control-Answer.  Then the home AAA
   server sends the reserved quota to the service element in the RADIUS
   Access-Accept.
</t><t>
   At the expiry of the allocated quota, the service element sends a new
   RADIUS Access-Request containing the units used this far to the home
   AAA server.  The home AAA server shall map a RADIUS Access-Request
   containing the reported units to the Diameter credit-control server
   in a Diameter Credit-Control-Request (UPDATE_REQUEST).  The Diameter
   credit-control server debits the used units from the end user's
   account and allocates a new quota that is returned to the home AAA
   server in the Diameter Credit-Control-Answer.  The quota is
   transferred to the service element in the RADIUS Access-Accept.  When
   the end user terminates the service, or when the entire quota has
   been used, the service element sends a RADIUS Access-Request.  To
   debit the used units from the end user's account and to stop the
   credit-control session, the home AAA server sends a Diameter
   Credit-Control-Request (TERMINATION_REQUEST) to the credit-control server.
   The Diameter credit-control server acknowledges the session
   termination by sending a Diameter Credit-Control-Answer to the home
   AAA server.  The RADIUS Access-Accept is sent to the NAS.
</t><t>
   A following diagram illustrates a RADIUS prepaid - Diameter credit-control
   interworking sequence.
</t>
<figure title="Message flow example with RADIUS prepaid - Diameter credit-control interworking"
        anchor="diam_rad_prepaid_flow">
<artwork><![CDATA[
Service Element         Translation Agent
  (e.g., NAS)               (CC Client)             CC Server
      |     Access-Request     |                        |
      |----------------------->|                        |
      |                        |    CCR (initial)       |
      |                        |----------------------->|
      |                        |    CCA (Granted-Units) |
      |                        |<-----------------------|
      |     Access-Accept      |                        |
      |     (Granted-Units)    |                        |
      |<-----------------------|                        |
      :                        :                        :
      |     Access-Request     |                        |
      |     (Used-Units)       |                        |
      |----------------------->|                        |
      |                        |    CCR (update,        |
      |                        |         Used-Units)    |
      |                        |----------------------->|
      |                        |    CCA (Granted-Units) |
      |                        |<-----------------------|
      |     Access-Accept      |                        |
      |     (Granted-Units)    |                        |
      |<-----------------------|                        |
      :                        :                        :
      |     Access-Request     |                        |
      |----------------------->|                        |
      |                        |     CCR (terminate,    |
      |                        |          Used-Units)   |
      |                        |----------------------->|
      |                        |     CCA                |
      |                        |<-----------------------|
      |     Access-Accept      |                        |
      |<-----------------------|                        |
      |                        |                        |
]]></artwork></figure>
</section>
<section anchor="sec-12" title="IANA Considerations">
<t>
    This document uses several registries that were originally created in
    <xref target="RFC4006"/> or the values assigned to existing namespaces
   managed by IANA. IANA [SHALL update/has updated] these to reference this
    document.  The registries and their allocation policies are below.</t>
<section anchor="sec-12.1" title="Application Identifier">
<t>
   This specification assigns the value 4, 'Diameter Credit Control', to
   the Application Identifier namespace defined in <xref target="RFC6733"/>.  See
   <xref target="sec-1.3"/> for more information.
</t>
</section>
<section anchor="sec-12.2" title="Command Codes">
<t>
   This specification uses the value 272 from the Command code namespace
   defined in <xref target="RFC6733"/> for the Credit-Control-Request (CCR) and
   Credit-Control-Answer (CCA) commands.
</t>
</section>
<section anchor="sec-12.3" title="AVP Codes">
<t>
   See <xref target="sec-8"/> for the assignment of the namespace in this specification.
</t>
<t>
  This document describes new AVP codes beyond those described in <xref target="RFC4006"/>.
  IANA is requested to allocate codes for the AVPs defined in the following
  <xref target="table_iana_avp_codes"/>.
</t>

<texttable anchor="table_iana_avp_codes" title="Requested AVP Assignments">
  <ttcol align="left">Attribute Name</ttcol>
  <ttcol align="left">Code</ttcol>
  <ttcol align="left">Defined in section</ttcol>
  <c>User-Equipment-Info-Extension</c><c>TBD1</c><c>8.52</c>
  <c>User-Equipment-Info-IMEISV</c><c>TBD2</c><c>8.53</c>
  <c>User-Equipment-Info-MAC</c><c>TBD3</c><c>8.54</c>
  <c>User-Equipment-Info-EUI64</c><c>TBD4</c><c>8.55</c>
  <c>User-Equipment-Info-ModifiedEUI64</c><c>TBD5</c><c>8.56</c>
  <c>User-Equipment-Info-IMEI</c><c>TBD6</c><c>8.57</c>
  <c>Subscription-Id-Extension</c><c>TBD7</c><c>8.58</c>
  <c>Subscription-Id-E164</c><c>TBD8</c><c>8.59</c>
  <c>Subscription-Id-IMSI</c><c>TBD9</c><c>8.60</c>
  <c>Subscription-Id-SIP-URI</c><c>TBD10</c><c>8.61</c>
  <c>Subscription-Id-NAI</c><c>TBD11</c><c>8.62</c>
  <c>Subscription-Id-Private</c><c>TBD12</c><c>8.63</c>
  <c>Redirect-Server-Extension</c><c>TBD13</c><c>8.64</c>
  <c>Redirect-Address-IPAddress</c><c>TBD14</c><c>8.65</c>
  <c>Redirect-Address-URL</c><c>TBD15</c><c>8.66</c>
  <c>Redirect-Address-SIP-URI</c><c>TBD16</c><c>8.67</c>
  <c>QoS-Final-Unit-Indication</c><c>TBD17</c><c>8.68</c>
</texttable>

</section>
<section anchor="sec-12.4" title="Result-Code AVP Values">
<t>
   This specification assigns the values 4010, 4011, 4012, 5030, 5031
   from the Result-Code AVP value namespace defined in <xref target="RFC6733"/>.  See
   <xref target="sec-9"/> for the assignment of the namespace in this specification.
</t>
</section>
<section anchor="sec-12.5" title="CC-Request-Type AVP">
<t>
   As defined in <xref target="sec-8.3"/>, the CC-Request-Type AVP includes
   Enumerated type values 1 - 4.  IANA has created and is maintaining a
   namespace for this AVP. The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.6" title="CC-Session-Failover AVP">
<t>
   As defined in <xref target="sec-8.4"/>, the CC-Failover-Supported AVP includes
   Enumerated type values 0 - 1.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.7" title="CC-Unit-Type AVP">
<t>
   As defined in <xref target="sec-8.32"/>, the CC-Unit-Type AVP includes Enumerated
   type values 0 - 5.  IANA has created and is maintaining a namespace
   for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.8" title="Check-Balance-Result AVP">
<t>
   As defined in <xref target="sec-8.6"/>, the Check-Balance-Result AVP includes
   Enumerated type values 0 - 1.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.9" title="Credit-Control AVP">
<t>
   As defined in <xref target="sec-8.13"/>, the Credit-Control AVP includes
   Enumerated type values 0 - 1.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.10" title="Credit-Control-Failure-Handling AVP">
<t>
   As defined in <xref target="sec-8.14"/>, the Credit-Control-Failure-Handling AVP
   includes Enumerated type values 0 - 2.  IANA has created and is
   maintaining a namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.11" title="Direct-Debiting-Failure-Handling AVP">
<t>
   As defined in <xref target="sec-8.15"/>, the Direct-Debiting-Failure-Handling AVP
   includes Enumerated type values 0 - 1.  IANA has created and is
   maintaining a namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.12" title="Final-Unit-Action AVP">
<t>
   As defined in <xref target="sec-8.35"/>, the Final-Unit-Action AVP includes
   Enumerated type values 0 - 2.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.13" title="Multiple-Services-Indicator AVP">
<t>
   As defined in <xref target="sec-8.40"/>, the Multiple-Services-Indicator AVP
   includes Enumerated type values 0 - 1.  IANA has created and is
   maintaining a namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.14" title="Redirect-Address-Type AVP">
<t>
   As defined in <xref target="sec-8.38"/>, the Redirect-Address-Type AVP includes
   Enumerated type values 0 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.15" title="Requested-Action AVP">
<t>
   As defined in <xref target="sec-8.41"/>, the Requested-Action AVP includes
   Enumerated type values 0 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.16" title="Subscription-Id-Type AVP">
<t>
   As defined in <xref target="sec-8.47"/>, the Subscription-Id-Type AVP  includes
   Enumerated type values 0 - 4.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.17" title="Tariff-Change-Usage AVP">
<t>
   As defined in <xref target="sec-8.27"/>, the Tariff-Change-Usage AVP includes
   Enumerated type values 0 - 2.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
<section anchor="sec-12.18" title="User-Equipment-Info-Type AVP">
<t>
   As defined in <xref target="sec-8.50"/>, the User-Equipment-Info-Type AVP includes
   Enumerated type values 0 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  The definition of new values
   is subject to the Specification Required policy <xref target="RFC8126"/> and
   conditions for enumerated values described in <xref target="RFC7423"/> Section 5.6.
</t>
</section>
</section>
<section anchor="sec-13" title="Credit-Control Application Related Parameters">
<t>
   Tx timer
</t><t>
      When real-time credit-control is required, the credit-control
      client contacts the credit-control server before and while the
      service is provided to an end user.  Due to the real-time nature
      of the application, the communication delays SHOULD be minimized;
      e.g., to avoid an overly long service setup time experienced by
      the end user.  The Tx timer is introduced to control the waiting
      time in the client in the Pending state.  When the Tx timer
      elapses, the credit-control client takes an action to the end user
      according to the value of the Credit-Control-Failure-Handling AVP
</t><t>
      or Direct-Debiting-Failure-Handling AVP.  The recommended value is
      10 seconds.
</t><t>
   Tcc timer
</t><t>
      The Tcc timer supervises an ongoing credit-control session in the
      credit-control server.  It is RECOMMENDED to use the Validity-Time
      as input to set the Tcc timer value.  In case of transient
      failures in the network, the Diameter credit-control server might
      change to Idle state.  To avoid this, the Tcc timer MAY be set so
      that Tcc equals to 2 x Validity-Time.
</t><t>
   Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling
</t><t>
      Client implementations may offer the possibility of locally
      configuring these AVPs.  In such a case their value and behavior
      is defined in <xref target="sec-5.7"/> for the Credit-Control-Failure-Handling
      and in <xref target="sec-6.5"/> for the Direct-Debiting-Failure-Handling.
</t>
</section>
<section anchor="sec-14" title="Security Considerations">
<t>
   Security considerations regarding the Diameter protocol itself are
   discussed in <xref target="RFC6733"/>.  Use of this application of Diameter MUST
   take into consideration the security issues and requirements of the
   base protocol.
</t>
<t>
   This application includes a mechanism for application layer replay
   protection by means of the Session-Id from <xref target="RFC6733"/> and
   CC-Request-Number, which is specified in this document.  The Diameter
   credit-control application is often used within one domain, and there
   may be a single hop between the peers.  In these environments, the
   use of TLS/TCP, DTLS/SCTP or IPsec is sufficient.  The details of TLS/TCP, DTLS/SCTP or IPsec
   related security considerations are discussed in the <xref target="RFC6733"/>.
</t><t>
   Because this application handles monetary transactions (directly or
   indirectly), it increases the interest for various security attacks.
   Therefore, all parties communicating with each other MUST be
   authenticated, including, for instance, TLS client-side
   authentication.  In addition, authorization of the client SHOULD be
   emphasized; i.e., that the client is allowed to perform credit-control
   for a certain user.  The specific means of authorization are
   outside of the scope of this specification but can be, for instance,
   manual configuration.
</t><t>
   Another kind of threat is malicious modification, injection, or
   deletion of AVPs or complete credit-control messages.  The credit-control
   messages contain sensitive billing related information (such
   as subscription Id, granted units, used units, cost information)
   whose malicious modification can have financial consequences.
   Sometimes simply delaying the credit-control messages can cause
   disturbances in the credit-control client or server.
</t><t>
    Even without any modification to the messages, an adversary that
    can eavesdrop on transactions can obtain privacy-sensitive
    information. Also, by monitoring the credit-control messages one
    can collect information about the
   credit-control server's billing models and business relationships.
</t><t>
   When third-party relays or proxy are involved, the hop-by-hop
   security does not necessarily provide sufficient protection for
   Diameter user session.  In some cases, it may be inappropriate to
   send Diameter messages, such as CCR and CCA, containing sensitive
   AVPs via untrusted Diameter proxy agents, as there are no assurances
   that third-party proxies will not modify the credit-control commands
   or AVP values.
</t>
<section anchor="sec-14.1" title="Direct Connection with Redirects">
<t>
   A Diameter credit-control agent cannot always know whether agents
   between it and the end user's Diameter credit-control server are
   reliable.  In this case, the Diameter credit-control agent doesn't
   have a routing entry in its Diameter Routing Table (defined in
   <xref target="RFC6733"/>, section 2.7) for the realm of the credit-control server
   in the end user's home realm.  The Diameter credit-control agent can
   have a default route configured to a local Redirect agent, and it
   redirects the CCR message to the redirect agent.  The local Redirect
   agent then returns a redirect notification (Result-code 3006,
   DIAMETER_REDIRECT_INDICATION) to the credit-control agent, as well as
   Diameter credit-control server(s) information (Redirect-Host AVP) and
   information (Redirect-Host-Usage AVP) about how the routing entry
   resulting from the Redirect-Host is to be used.  The Diameter
   credit-control agent then forwards the CCR message directly to one of
   the hosts identified by the CCA message from the redirect agent.  If
   the value of the Redirect-Host-Usage AVP is unequal to zero, all
   following messages are sent to the host specified in the Redirect-Host
   AVP until the time specified by the Redirect-Max-Cache-Time AVP
   is expired.
</t><t>
   There are some authorization issues even with redirects.  There may
   be attacks toward nodes that have been properly authorized, but that
   abuse their authorization or have been compromised.  These issues are
   discussed more widely in <xref target="RFC4072"/>, Section 8.
</t>
</section>
<section anchor="sec-14.2" title="Application Level Redirects">
<t>
    This document includes a redirection facility in <xref target="sec-5.6.2"/>,
    whereby the service provider can redirect (in an application-specific way) 
    the end user to an alternate location when their credits have expired.  This is
    useful in that it allows for the user to return to normal service quickly, 
    but also exposes additional risks and attack surface.  In particular, 
    this redirection can potentially occur at an arbitrary point in a user's session, 
    potentially without any additional contextual confirmation available 
    to the user that the redirection is driven by the network.  This lack of 
    confirmation matters, because, in many application protocols, the communication
    peer is also capable of inducing redirection. When the peer is an attacker, 
    the redirection can be to an attacker-controlled site. In particular, 
    such sites may be "phishing" sites designed to appear similar to legitimate 
    payment sites in an attempt to obtain users' payment information for fraudulent uses. 
    When users become used to such redirection, they may have difficulty distinguishing such
    attacks from legitimate redirections.
</t>
<t>
    Because of the potentially harmful consequences of arbitrary redirection by an 
    attacker (such as to phishing sites), it is important for service providers to be aware 
    of that risk and assure their users are aware of it as well. Service providers should 
    follow industry best practices for the specific application layer protocol to reduce 
    the chances that such attacks could be mistaken for legitimate redirection. The details
    of such practice are out of scope for this document.
</t>
</section>
</section>
<section anchor="sec-15" title="Privacy Considerations">
<t>
   As the Diameter protocol, and especially credit-control application, 
   deals with subscribers and their actions, extra care should be taken regarding 
   the privacy of the subscribers. In terms of <xref target="RFC6973"/>, 
   both the credit-control client and credit-control server are intermediary entities,
   wherein the subscribers' privacy may be compromised even if no security issues exist, 
   and only authorized entities have access to the privacy-sensitive information.
</t>
<section anchor="sec-15.1" title="Privacy Sensitive AVPs">
<t>The privacy-sensitive AVPs listed in this section MUST NOT be sent across non-trusted networks or Diameter agents without end-to-end authentication and confidentiality protection, as described in <xref target="RFC6733"/> section 13.3.
</t>
<t>
   The following AVPs contain privacy-sensitive information at different levels:
<list style="numbers">
<t>
   CC-Correlation-Id AVP: may contain privacy-sensitive information as the service-provider may encode 
   personal information that helps it correlate different subscriptions and access technologies.
</t><t>
   Check-Balance-Result AVP: contains information on the balance status of the subscriber.
</t><t>
   Currency-Code AVP: contains information on the subscriber's locale.
</t><t>
   Cost-Unit AVP: contains privacy-sensitive information, as a human readable format of the Cost-Information AVP.
</t><t>
   Service-Identifier AVP: may contain privacy-sensitive information about the subscriber's internet activity.
</t><t>
   Rating-Group AVP: may contain privacy-sensitive information about the subscriber's internet activity.
</t><t>
   Restriction-Filter-Rule AVP: the information inside IPFilterRule may be used to infer
   services used by the subscriber.
</t><t>
   Redirect-Server-Address AVP: the service-provider might embed personal information on the subscriber in
   the URL/I (e.g. to create a personalized message). However, the service-provider may anonymise the subscriber's
   identity instead in the URL/I, and let the redirect server query the information directly. Such anonymized 
   information must not allow personal information or the subscriber's identity to be easily guessed. Furthermore, 
   the service-provider should treat the URL/I schema itself as confidential, and make sure it cannot be inferred 
   from observation of the traffic, or due to its trivial structure. A trivial structure could allow an adversary to query/modify 
   personal information even without knowing the subscriber's identity. Similar AVPs are: 
   Redirect-Address-URL, Redirect-Address-SIP-URI.
</t><t>
   Service-Context-Id AVP: depending with how the service-provider uses it, it may contain privacy-sensitive information 
   about the service (e.g. in a 3GPP network Service-Context-Id AVP has a different value for: Packet Switching, SMS and MMS etc.)
</t><t>
   Service-Parameter-Info AVP: depending with how the service-provider uses it, it may contain privacy-sensitive information 
   about the subscriber (e.g. location).
</t><t>
   Subscription-Id-Data AVP: contains the identity of the subscriber. Similar AVPs are: Subscription-Id-E164,
   Subscription-Id-IMSI, Subscription-Id-SIP-URI, Subscription-Id-NAI, Subscription-Id-Private.
</t><t>
   User-Equipment-Info-Value AVP: contains the identity of the device of the subscriber. Similar AVPs are: 
   User-Equipment-Info-IMEISV, User-Equipment-Info-MAC, User-Equipment-Info-EUI64, User-Equipment-Info-ModifiedEUI64, User-Equipment-Info-IMEI.
</t><t>
   QoS-Final-Unit-Indication AVP: grouped AVP which may contains privacy-sensitive information in its sub-AVPs (e.g IPFilterRule, redirect address).
</t>
</list>
</t>
<t>
   Note that some AVPs which are used in this document are defined in <xref target="RFC6733"/> and may contain privacy-sensitive information.
   These AVPs are not listed above.
</t>
</section>
<section anchor="sec-15.2" title="Data Minimization">
<t>
   Due to the nature of the credit-control application, some personal data and identity information 
   must be stored in both credit-control client and credit-control server. This, however, 
   could be minimized by following these guidelines:
  <list style="numbers">
   <t>
   Data stored in the credit-control client does not need to be persisted across sessions. 
   All data could be deleted once the session end, and reconstructed once a new session is initialized. 
   Note that, while the credit-control server is usually owned by the service provider with 
   which the subscriber already has some direct legal or business relationship 
   (where privacy level could be agreed upon), this is not always true for the credit-control client, 
   that may be owned by a third-party.
   </t><t>
   Some information about the subscriber has to be stored in persistent storage in the credit-control 
   server (e.g. identity, balance), however, per transaction information does not have to be stored in persistent storage,
   and per session information may be deleted from persistent storage once the session ends.
   </t><t>
   In some cases, per transaction information has to be stored on the credit-control server, 
   client, or both, for regulatory, auditability or debugging reasons. However, this could be minimized by
   following these guidelines:
   <list style="letters">
    <t>
    Data retention does not need to exceed the required duration.
    </t><t>
    Transaction information could be aggregated in some cases. E.g. prefer information per sessions over
    information per rating-group; prefer hourly byte summary over per transaction byte counts.
    </t><t>
    If not strictly needed, the more sensitive information (E.g. location, equipment type) could be 
    filtered out of such logs. This information is often used to make rating decisions, 
    and in this case, the rating decision should be logged instead of the data used to make them.
    </t><t>
    Due to the reasons explained in 1, the credit-control server would be a preferred location for storing
    such transaction information, instead of the credit-control client
    </t>
   </list>
   </t>
  </list>
</t>
</section>
<section anchor="sec-15.3" title="Diameter Agents">
<t>
   Diameter agents, as described in <xref target="RFC6733"/>, may be owned by third-parties. If end-to-end 
   security is supported between credit-control client and credit-control server, the operator can use it to encrypt
   privacy-sensitive AVPs (as listed in <xref target="sec-15.1"/>), and prevent such information from 
   leaking into the agent. 
</t>
<t>
   In some cases, the Diameter agent needs access into privacy-sensitive AVPs, in order to take
   correct routing decisions, or even modify the content of these AVPs. For example, a proxy agent may 
   need to look into the Subscription-Id-IMSI AVP, in order to extract the mobile country and network codes 
   of the user, and use them to lookup the destination to which the request should be routed 
   (see: section 2.8.2 in <xref target="RFC6733"/>). In such a case, the credit-control client and credit-control 
   server may use a mechanism that anonymizes the identity of the subscriber, as well as a mechanism 
   to encrypt other AVPs not used by the agent.
</t>
</section>
</section>
 </middle>

 <!--  *****BACK MATTER ***** -->

 <back>
   <references title="Normative References">
     <!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?-->
     &RFC6733;

     &RFC3261;

     &RFC7542;

      <reference anchor="E164">
       <front>
         <title>Recommendation E.164/I.331 (05/97): The International
               Public Telecommunication Numbering Plan.</title>
         <author></author>
         <date year="1997" />
       </front>
     </reference>

     <reference anchor="CE164">
       <front>
         <title>Complement to ITU-T Recommendation E.164 (05/1997):"List
               of ITU-T Recommendation E.164 assigned country codes"</title>
         <author></author>
         <date year="June 2000" />
       </front>
     </reference>

     <reference anchor="E212">
       <front>
         <title>Recommendation E.212 (11/98): The international
               identification plan for mobile terminals and mobile
               users.</title>
         <author></author>
         <date year="1998" />
       </front>
     </reference>

     <reference anchor="CE212">
       <front>
         <title>Complement to ITU-T Recommendation E.212 (11/1997):" List
               of mobile country or geographical area codes"</title>
         <author></author>
         <date year="February 1999" />
       </front>
     </reference>

     &RFC8126;

     &RFC791;

     &RFC4291;

     &RFC5952;

     &RFC2119;

     <reference anchor="ISO4217">
       <front>
         <title>Codes for the representation of currencies and funds,
               International Standard ISO 4217</title>
         <author></author>
         <date year="2001" />
       </front>
     </reference>

     &RFC7155;

     &RFC3539;

     &RFC3986;

     &RFC4006;

     &RFC5777;

    <reference anchor="EUI64" target="http://standards.ieee.org/regauth/oui/tutorials/EUI64.html ">
       <front>
         <title>"Guidelines for 64-bit Global Identifier (EUI-64)
               Registration Authority"</title>
         <author><organization>IEEE</organization></author>
         <date year="March 1997" />
       </front>
     </reference>

    <reference anchor="TGPPIMEI">
       <front>
         <title>Technical
               Specification Group Core Network, Numbering, addressing
               and identification, (release 13), 3GPP TS 23.003 v. 13.5.0</title>
         <author><organization>3rd Generation Partnership Project</organization></author>
         <date year="2016-04" />
       </front>
     </reference>

     &RFC7423;
     
     &RFC8174;

   </references>

   <references title="Informative References">
     &RFC2866;

     &RFC4004;

     &RFC4072;

     &RFC3725;

     &RFC3580;

     &RFC6973;

     <reference anchor="TGPPCHARG">
       <front>
         <title>Technical
               Specification Group Services and System Aspects, Service
               aspects; Charging and Billing, (release 13), 3GPP TS
               22.115 v. 13.3.0</title>
         <author><organization>3rd Generation Partnership Project</organization></author>

         <date year="2016-03" />
       </front>
     </reference>
   </references>

<section anchor="Acknowledgements" title="Acknowledgements">
   <t>The original authors of RFC4006 are:
      Harri Hakala, Leena Mattila, Juha-Pekka Koskinen,
      Marco Stura, and John Loughney.
      </t>
     <t>The authors would like to thank Bernard Aboba, Jari Arkko, Robert
   Ekblad, Pasi Eronen, Benny Gustafsson, Robert Karlsson, Avi Lior,
   Paco Marin, Jussi Maki, Jeff Meyer, Anne Narhi, John Prudhoe,
   Christopher Richards, Juha Vallinen, and Mark Watson for their
   comments and suggestions.</t>
</section>

<section anchor="app-a" title="Credit-Control Sequences">
  <section anchor="app-a1" title="Flow I">
   <figure anchor="flow1" title="Flow I">
<artwork><![CDATA[
                           NAS
End User          (CC Client)         AAA Server           CC Server
  |(1)User Logon      |(2)AA Request (CC AVPs)                  |
  |------------------>|------------------->|                    |
  |                   |                    |(3)CCR(initial, CC AVPs)
  |                   |                    |------------------->|
  |                   |                    | (4)CCA(Granted-Units)
  |                   |                    |<-------------------|
  |                   |(5)AA Answer(Granted-Units)              |
  |(6)Access granted  |<-------------------|                    |
  |<----------------->|                    |                    |
  |                   |                    |                    |
  :                   :                    :                    :
  |                   |(7)CCR(update,Used-Units)                |
  |                   |------------------->|(8)CCR              |
  |                   |                    |   (update,Used-Units)
  |                   |                    |------------------->|
  |                   |                    |(9)CCA(Granted-Units)
  |                   |(10)CCA(Granted-Units)<------------------|
  |                   |<-------------------|                    |
  :                   :                    :                    :
  |         (Auth. lifetime expires)       |                    |
  |                   |(11) AAR (CC AVP)   |                    |
  |                   |------------------->|                    |
  |                   |          (12) AAA  |                    |
  |                   |<-------------------|                    |
  :                   :                    :                    :
  :                   :                    :                    :
  |(13) User logoff   |                    |                    |
  |------------------>|(14)CCR(term.,Used-Units)                |
  |                   |------------------->|(15)CCR             |
  |                   |                    |   (term.,Used-Units)
  |                   |                    |------------------->|
  |                   |                    |            (16)CCA |
  |                   |            (17)CCA |<-------------------|
  |                   |<-------------------|                    |
  |                   |(18)STR             |                    |
  |                   |------------------->|                    |
  |                   |            (19)STA |                    |
  |                   |<-------------------|                    |
]]></artwork>
    </figure>
<t>A credit-control flow for Network Access Services prepaid is shown in
   <xref target="flow1"/>.
   The Diameter <xref target="RFC7155"/> is implemented in the Network
   Access Server (NAS).  The focus of this flow is in the credit
   authorization.
</t>
<t>
   The user logs on to the network (1).  The Diameter NAS sends a
   Diameter AA-Request (AAR) to the home Diameter AAA server.  The
   credit-control client populates the AAR with the Credit-Control AVP
   set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,
   as usual <xref target="RFC7155"/>.  The home Diameter AAA server performs
   service-specific Authentication and Authorization, as usual.  The home
   Diameter AAA server determines that the user is a prepaid user and
   notices from the Credit-Control AVP that the NAS has credit-control
   capabilities.  It sends a Diameter Credit-Control-Request with
   CC-Request-Type set to INITIAL_REQUEST to the Diameter credit-control
   server to perform credit authorization (3) and to establish a
   credit-control session.  (The home Diameter AAA server may forward
   service-specific AVPs received from the NAS as input for the rating
   process.)  The Diameter credit-control server checks the end user's
   account balance, rates the service, and reserves credit from the end
   user's account.  The reserved quota is returned to the home Diameter
   AAA server in the Diameter Credit-Control-Answer (4).  The home
   Diameter AAA server sends the reserved quota to the NAS in the
   Diameter AA-Answer (AAA).  Upon successful AAA, the NAS starts the
   credit-control session and starts monitoring the granted units (5).
   The NAS grants access to the end user (6).  At the expiry of the
   allocated quota, the NAS sends a Diameter Credit-Control-Request with
   CC-Request-Type set to UPDATE_REQUEST to the Home Diameter AAA server
   (7).  This message contains the units used thus far.  The home
   Diameter AAA server forwards the CCR to the Diameter credit-control
   server (8).  The Diameter credit-control server debits the used units
   from the end user's account and allocates a new quota that is
   returned to the home Diameter AAA server in the Diameter
   Credit-Control-Answer (9).  The message is forwarded to the NAS (10).
   During the ongoing credit-control session, the authorization lifetime
   expires, and the authorization/authentication client in the NAS
   performs service-specific re-authorization to the home Diameter AAA
   server, as usual.  The credit-control client populates the AAR with
   the Credit-Control AVP set to RE_AUTHORIZATION, indicating that the
   credit-control server shall not be contacted, as the credit
   authorization is controlled by the burning rate of the granted units
   (11).  The home Diameter AAA server performs service-specific
   re-authorization as usual and returns the AA-Answer to the NAS (12).
   The end user logs off from the network (13).  To debit the used units
   from the end user's account and to stop the credit-control session,
   the NAS sends a Diameter Credit-Control-Request with CC-Request-Type
   set to TERMINATION_REQUEST to the home Diameter AAA server (14).  The
   home Diameter AAA server forwards the CCR to the credit-control
   server (15).  The Diameter credit-control server acknowledges the
   session termination by sending a Diameter Credit-Control-Answer to
   the home Diameter AAA server (16).  The home Diameter AAA server
   forwards the answer to the NAS (17).  STR/STA takes place between the
   NAS and home Diameter AAA server, as usual (18-19).
</t>
  </section>
  <section anchor="app-a2" title="Flow II">
    <figure anchor="flow2" title="Flow II">
<artwork><![CDATA[
      SIP Proxy/Registrar   AAA
A           (CC Client)     Server           B        CC Server
|(i)  REGISTER |              |              |              |
|------------->|(ii)          |              |              |
|              |------------->|              |              |
|              |authentication &             |              |
|              |authorization |              |              |
|              |<-------------|              |              |
|(iii)200 OK   |                             |              |
|<-------------|                             |              |
:              :                             :              :
|(1)  INVITE   |                                            :
|------------->|
|              |(2)  CCR (Initial, SIP-specific AVP)        |
|              |------------------------------------------->|
|              |(3)  CCA (Granted-Units)                    |
|              |<-------------------------------------------|
|              |(4)  INVITE                  |              |
|              |---------------------------->|              |
:              :                             :              :
|              |(5)  CCR (update, Used-Units)               |
|              |------------------------------------------->|
|              |(6)  CCA (Granted-Units)                    |
|              |<-------------------------------------------|
:              :                             :              :
|(7)  BYE      |                             |              |
|------------->|                             |              |
|              |(8)  BYE                     |              |
|              |---------------------------->|              |
|              |(9)  CCR (termination, Used-Units)          |
|              |------------------------------------------->|
|              |(10) CCA ()                                 |
|              |<-------------------------------------------|
|              |                             |              |
]]></artwork>
    </figure>
<t>
   This is an example of Diameter credit-control for SIP sessions.
   Although the flow focuses on illustrating the usage of credit-control
   messages, the SIP signaling is inaccurate, and the diagram is not by
   any means an attempt to define a service provider's SIP network.
   However, for the sake of this example, some assumptions are made
   below.
</t>
<t>
   Typically, prepaid services based, for example, on time usage for SIP
   session require an entity in the service provider network to
   intercept all the requests within the SIP dialog in order to detect
   events, such as session establishment and session release, that are
   essential to perform credit-control operations with the credit-control
   server.  Therefore, in this example, it is assumed that the
   SIP Proxy adds a Record-Route header in the initial SIP INVITE to
   make sure that all the future requests in the created dialog traverse
   through it (for the definitions of 'Record-Route' and 'dialog' please
   refer to <xref target="RFC3261"/>).  Finally, the degree of credit-control measuring of
   the media by the proxy depends on the business model design used in
   setting up the end system and proxies in the SIP network.
</t>
<t>
   The end user (SIP User Agent A) sends REGISTER with credentials (i).
   The SIP Proxy sends a request to the home AAA server to perform
   Multimedia authentication and authorization by using, for instance,
   Diameter Multimedia application (ii).  The home AAA server checks
   that the credentials are correct and checks the user profile.
   Eventually, 200 OK response (iii) is sent to the UA.  Note that the
   Authentication and Authorization is valid for the registration
   validity period duration (i.e., until re-registration is performed).
   Several SIP sessions may be established without re-authorization.
</t>
<t>
   UA A sends an INVITE (1).  The SIP Proxy sends a Diameter
   Credit-Control-Request (INITIAL_REQUEST) to the Diameter credit-control
   server (2).  The Credit-Control-Request contains information obtained
   from the SIP signaling describing the requested service (e.g.,
   calling party, called party, Session Description Protocol
   attributes).  The Diameter credit-control server checks the end
   user's account balance, rates the service, and reserves credit from
   the end user's account.  The reserved quota is returned to the SIP
   Proxy in the Diameter Credit-Control-Answer (3).  The SIP Proxy
   forwards the SIP INVITE to UA B (4).  B's phone rings, and B answers.
   The media flows between them, and the SIP Proxy starts measuring the
   quota.  At the expiry of the allocated quota, the SIP Proxy sends a
   Diameter Credit-Control-Request (UPDATE_REQUEST) to the Diameter
   credit-control server (5).  This message contains the units used thus
   far.  The Diameter credit-control server debits the used units from
   the end user's account and allocates new credit that is returned to
   the SIP Proxy in the Diameter Credit-Control-Answer (6).  The end
   user terminates the service by sending a BYE (7).  The SIP Proxy
   forwards the BYE message to UA B (8) and sends a Diameter
   Credit-Control-Request (TERMINATION_REQUEST) to the credit-control server
   (9).  The Diameter credit-control server acknowledges the session
   termination by sending a Diameter Credit-Control-Answer to the SIP
   Proxy (10).
</t>
  </section>
  <section anchor="app-a3" title="Flow III">
    <figure anchor="flow3" title="Flow III">
    <artwork><![CDATA[
                         MMS Server
             A           (CC Client)           B           CC Server
             |(1) Send MMS    |                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, DIRECT_DEBITING,|
             |                |          MMS-specific AVP)      |
             |                |-------------------------------->|
             |                |(3)  CCA (Granted-Units)         |
             |                |<--------------------------------|
             |(4) Send MMS Ack|                |                |
             |<---------------|                |                |
             |                |(5) Notify MMS  |                |
             |                |--------------->|                |
             :                :                :                :
             |                |(6) Retrieve MMS|                |
             |                |<---------------|                |
             |                |(7) Retrieve MMS|                |
             |                |    Ack         |                |
             |                |--------------->|                |
             |                |                |                |
    ]]></artwork>
      </figure>
    <t>
        This is an example of Diameter credit-control for direct debiting
        using the Multimedia Messaging Service environment.  Although the
        flow focuses on illustrating the usage of credit-control messages,
        the MMS signaling is inaccurate, and the diagram is not by any means
        an attempt to define any service provider's MMS configuration or
        billing model.
    </t>
<t>
   A credit-control flow for Multimedia Messaging Services is shown in
   <xref target="flow3"/>.  The sender is charged as soon as the messaging server
   successfully stores the message.
</t>
<t>
   The end user A sends a Multimedia Message (MMS) to the MMS server
   (1).  The MMS server stores the message and sends a Diameter
   Credit-Control-Request (EVENT_REQUEST with Requested-Action DIRECT_DEBITING)
   to the Diameter credit-control server (2).  The Credit-Control-Request
   contains information about the MMS message (e.g., size,
   recipient address, image coding type).  The Diameter credit-control
   server checks the end user's account balance, rates the service, and
   debits the service from the end user's account.  The granted quota is
   returned to the MMS server in the Diameter Credit-Control-Answer (3).
   The MMS server acknowledges the successful reception of the MMS
   message (4).  The MMS Server notifies the recipient about the new MMS
   (5), and end user B retrieves the message from the MMS message store
   (6),(7).
</t>
<t>
    Note that the transfer of the MMS message can take an extended time
    and can fail, in which case a recovery action is needed.  The MMS
    server should return the already debited units to the user's account
    by using the REFUND action described in <xref target="sec-6.4"/>.
</t>
  </section>
  <section anchor="app-a4" title="Flow IV">
    <figure anchor="flow4" title="Flow IV">
    <artwork><![CDATA[
                          MMS Server
      Content Server     (CC Client)           B           CC Server
             |(1) Send MMS    |                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, CHECK_BALANCE,  |
             |                |          MMS-specific AVP)      |
             |                |-------------------------------->|
             |                |(3)  CCA (ENOUGH_CREDIT)         |
             |                |<--------------------------------|
             |(4) Send MMS Ack|                |                |
             |<---------------|                |                |
             |                |(5) Notify MMS  |                |
             |                |--------------->|                |
             :                :                :                :
             |                |(6) Retrieve MMS|                |
             |                |<---------------|                |
             |                |(7)  CCR (event, DIRECT_DEBITING,|
             |                |          MMS-specific AVP)      |
             |                |-------------------------------->|
             |                |(8)  CCA (Granted-Units)         |
             |                |<--------------------------------|
             |                |(9) Retrieve MMS|                |
             |                |    Ack         |                |
             |                |--------------->|                |
             |                |                |                |
    ]]></artwork>
    </figure>
<t>
   This is an example of Diameter credit-control for direct debiting
   using the Multimedia Messaging Service environment.  Although the
   flow focuses on illustrating the usage of credit-control messages,
   the MMS signaling is inaccurate, and the diagram is not by any means
   an attempt to define any service provider's MMS configuration or
   billing model.
</t>
<t>
   A credit-control flow for Multimedia Messaging Service is shown in
   <xref target="flow4"/>.  The recipient is charged at the message delivery.
</t>
<t>
  A content server sends a Multimedia Message (MMS) to the MMS server
   (1) that stores the message.  The message recipient will be charged
   for the MMS message in this case.  As there can be a substantially
   long time between the receipt of the message at the MMS server and
   the actual retrieval of the message, the MMS server does not
   establish any credit-control session to the Diameter credit-control
   server but performs first only a balance check (without any credit
   reservation) by sending a Diameter Credit-Control-Request
   (EVENT_REQUEST with Requested-Action CHECK_BALANCE) to verify that
   end user B can cover the cost for the MMS (2).  The Diameter credit-control
   server checks the end user's account balance and returns the
   answer to the MMS server in the Diameter Credit-Control-Answer (3).
   The MMS server acknowledges the successful reception of the MMS
   message (4).  The MMS server notifies the recipient of the new MMS
   (5), and after some time end user B retrieves the message from the
   MMS message store (6).  The MMS server sends a Diameter
   Credit-Control-Request (EVENT_REQUEST with Requested-Action:
   DIRECT_DEBITING) to the Diameter credit-control server (7).  The
   Credit-Control-Request contains information about the MMS message
   (e.g., size, recipient address, coding type).  The Diameter credit-control
   server checks the end user's account balance, rates the
   service, and debits the service from the end user's account.  The
   granted quota is returned to the MMS server in the Diameter
   Credit-Control-Request (8).  The MMS is transferred to end user B (9).
</t>
<t>
   Note that the transfer of the MMS message can take an extended time
   and can fail, in which case a recovery action is needed.  The MMS
   server should return the already debited units to the user's account
   by using the REFUND action described in <xref target="sec-6.4"/>.
</t>
   </section>
  <section anchor="app-a5" title="Flow V">
    <figure anchor="flow5" title="Flow V">
    <artwork><![CDATA[
                        SIP Controller
             A           (CC Client)           B           CC Server
             |(1)INVITE B(SDP)|                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, PRICE_ENQUIRY,  |
             |                |          SIP-specific AVPs)     |
             |                |-------------------------------->|
             |                |(3)  CCA (Cost-Information)      |
             |                |<--------------------------------|
             | (4)MESSAGE(URL)|                |                |
             |<---------------|                |                |
             |(5)HTTP GET     |                |                |
             |--------------->|                |                |
             |(6)HTTP POST    |                |                |
             |--------------->|(7)INVITE(SDP)  |                |
             |                |--------------->|                |
             |                |      (8)200 OK |                |
             |      (9)200 OK |<---------------|                |
             |<---------------|                |                |
    ]]></artwork>
    </figure>
<t>
   This is an example of Diameter credit-control for SIP sessions.
   Although the flow focuses on illustrating the usage of credit-control
   messages, the SIP signaling is inaccurate, and the diagram is not by
   any means an attempt to define a service provider's SIP network.
</t>
<t>
   <xref target="flow5"/> is an example of Advice of Charge (AoC) service for SIP
   call.  User A can be either a postpaid or prepaid subscriber using
   the AoC service.  It is assumed that the SIP controller also has HTTP
   capabilities and delivers an interactive AoC web page with, for
   instance, the cost information, the details of the call derived from
   the SDP, and a button to accept/not accept the charges.  (There may
   be many other ways to deliver AoC information; however, this flow
   focuses on the use of the credit-control messages.)  The user has
   been authenticated and authorized prior to initiating the call and
   subscribed to AoC service.
</t>
<t>
   UA A sends an INVITE with SDP to B (1).  The SIP controller
   determines that the user is subscribed to AoC service and sends a
   Diameter Credit-Control-Request (EVENT_REQUEST with Requested-Action:
   PRICE_ENQUIRY) to the Diameter credit-control server (2).  The
   Credit-Control-Request contains SIP-specific AVPs derived from the
   SIP signaling, describing the requested service (e.g., calling party,
   called party, Session Description Protocol attributes).  The Diameter
   credit-control server determines the cost of the service and returns
   the Credit-Control-Answer including the Cost-Information AVP (3).
   The SIP controller manufactures the AoC web page with information
   received in SIP signaling and with the cost information received from
   the credit-control server.  Then it sends a SIP MESSAGE that contains
   a URL pointing to the AoC information web page (4).  At the receipt
   of the SIP MESSAGE, A's UA automatically invokes the web browser that
   retrieves the AoC information (5).  The user clicks on a proper
   button and accepts the charges (6).  The SIP controller continues the
   session and sends the INVITE to the B party, which accepts the call
   (7,8,9).
</t>
  </section>
  <section anchor="app-a6" title="Flow VI">
    <figure anchor="flow6" title="Flow VI">
    <artwork><![CDATA[
                       Gaming Server
End User                (CC Client)              CC Server
   |  (1)Service Delivery   |                        |
   |<---------------------->|                        |
   :                        :                        :
   :                        :                        :
   |                        |(2)CCR(event,REFUND,Requested-
   |                        |Service-Unit,Service-Parameter-Info)
   |                        |----------------------->|
   |                        |  (3)CCA(Cost-Information)
   |                        |<-----------------------|
   |        (4)Notification |                        |
   |<-----------------------|                        |
    ]]></artwork>
    </figure>
<t>
   <xref target="flow6"/> illustrates a credit-control flow for the REFUND case.  It
   is assumed that there is a trusted relationship and secure connection
   between the Gaming server and the Diameter credit-control server.
   The end user may be a prepaid subscriber or a postpaid subscriber.
</t>
<t>
   While the end user is playing the game (1), she enters a new level
   that entitles her to a bonus.  The Gaming server sends a Diameter
   Credit-Control-Request (EVENT_REQUEST with Requested-Action:
   REFUND_ACCOUNT) to the Diameter credit-control server (2).  The
   Credit-Control-Request Request contains the Requested-Service-Unit
   AVP with the CC-Service-Specific-Units containing the number of
   points the user just won.  The Service-Parameter-Info AVP is also
   included in the request and specifies the service event to be rated
   (e.g., Tetris Bonus).  From information received, the Diameter
   credit-control server determines the amount to be credited, refunds
   the user's account, and returns the Credit-Control-Answer, including
   the Cost-Information AVP (3).  The Cost-Information indicates the
   credited amount.  At the first opportunity, the Gaming server
   notifies the end user of the credited amount (4).
</t>
  </section>
  <section anchor="app-a7" title="Flow VII">
    <figure anchor="flow7" title="Flow VII">
    <artwork><![CDATA[
          SIP Controller    Top-Up
A          (CC Client)      Server           B      CC Server
|               |              |             |              |
|               | (1) CCR(Update,Used-Unit)  |              |
|               |------------------------------------------>|
|               |              (2) CCA(Final-Unit, Redirect)|
|               |<------------------------------------------|
:               :              :             :              :
:               :              :             :              :
|               | (3) CCR(Update, Used-Units)|              |
|               |------------------------------------------>|
|               | (3a)INVITE("hold")         |              |
|               |--------------------------->|              |
|               |              |      (4) CCA(Validity-Time)|
|               |<------------------------------------------|
|     (5)INVITE | (6)INVITE    |             |              |
|<--------------|------------->|             |              |
|            (7)RTP            |             |              |
|..............................|             |              |
|               |       (8)BYE |             |              |
|               |<-------------|             |              |
|               | (9)CCR(Update)             |              |
|               |------------------------------------------>|
|               |                     (10)CCA(Granted-Unit) |
|               |<------------------------------------------|
|    (12)INVITE | (11)INVITE                 |              |
|<--------------|--------------------------->|              |
    ]]></artwork>
    </figure>
<t>
   <xref target="flow7"/> is an example of the graceful service termination for a
   SIP call.  It is assumed that the call is set up so that the
   controller is in the call as a B2BUA (Back to Back User Agent)
   performing third-party call control (3PCC).  Note that the SIP
   signaling is inaccurate, as the focus of this flow is in the graceful
   service termination and credit-control authorization.  The best
   practice for 3PCC is defined in <xref target="RFC3725"/>.
</t>
<t>
   The call is ongoing between users A and B; user A has a prepaid
   subscription.  At the expiry of the allocated quota, the SIP
   controller sends a Diameter Credit-Control-Request (UPDATE_REQUEST)
   to the Diameter credit-control server (1).  This message contains the
   units used thus far.  The Diameter credit-control server debits the
   used units from the end user's account and allocates the final quota
   returned to the SIP controller in the Diameter Credit-Control-Answer
   (2).  This message contains the Final-Unit-Indication AVP with the
   Final-Unit-Action set to REDIRECT, the Redirect-Address-Type set to
   SIP URI, and the Redirect-Server-Address set to the Top-up server
   name (e.g., sip:sip-topup-server@domain.com).  At the expiry of the
   final allocated quota, the SIP controller sends a Diameter
   Credit-Control-Request (UPDATE_REQUEST) to the Diameter credit-control
   server (3) and places the called party on "hold" by sending an INVITE
   with the appropriate connection address in the SDP (3a).  The
   Credit-Control-Request message contains the units used thus far.  The
   Diameter credit-control server debits the used units from the end
   user's account but does not make any credit reservation.  The
   Credit-Control-Answer message, which contains the Validity-Time to
   supervise the graceful service termination, is returned to the SIP
   controller (4).  The SIP controller establishes a SIP session between
   the prepaid user and the Top-up server (5, 6).  The Top-up server
   plays an announcement and prompts the user to enter a credit card
   number and the amount of money to be used to replenish the account
   (7).  The Top-up server validates the credit card number and
   replenishes the user's account (using some means outside the scope of
   this specification) and releases the SIP session (8).  The SIP
   controller can now assume that communication between the prepaid user
   and the Top-up server took place.  It sends a spontaneous
   Credit-Control-Request (UPDATE_REQUEST) to the Diameter credit-control
   server to check whether the account has been replenished (9).  The
   Diameter credit-control server reserves credit from the end user's
   account and returns the reserved quota to the SIP controller in the
   Credit-Control-Answer (10).  At this point, the SIP controller
   re-connects the caller and the called party (11,12).
</t>
  </section>
  <section anchor="app-a8" title="Flow VIII">
    <figure anchor="flow8" title="Flow VIII">
    <artwork><![CDATA[
                       NAS                           Top-up      CC
End-User         (CC Client)          AAA Server    Server    Server
   |(1)User Logon      |(2)AA Request (CC AVPs)        |         |
   |------------------>|------------------->|          |         |
   |                   |                    |(3)CCR(initial, CC AVPs)
   |                   |                    |------------------->|
   |                   |                    |(4)CCA(Final-Unit,  |
   |                   |                    |      Validity-Time)|
   |                   |                    |<-------------------|
   |                   |(5)AA Answer(Final-Unit,Validity-Time)   |
   |(6)Limited Access  |<-------------------|          |         |
   |      granted      |                    |          |         |
   |<----------------->|                    |          |         |
   |                   |                    |          |         |
   |   (7)TCP/HTTP     |        (8)TCP/HTTP            |         |
   |<----------------->|<----------------------------->|         |
   |                 (9) Replenish account             |         |
   |<------------------------------------------------->|         |
   |                   |                    |            (10)RAR |
   |                   |<-------------------|<-------------------|
   |                   | (11) RAA           |                    |
   |                   |------------------->|------------------->|
   |                   |(12)CCR(update)     |                    |
   |                   |------------------->|(13)CCR(Update)     |
   |                   |                    |------------------->|
   |                   |                    |(14)CCA(Granted-Units)
   |                   |(15)CCA(Granted-Units)<------------------|
   |                   |<-------------------|                    |
    ]]></artwork>
    </figure>
<t>
   <xref target="flow8"/> is an example of the graceful service termination
   initiated when the first interrogation takes place because the user's
   account is empty.  In this example, the credit-control server
   supports the server-initiated credit re-authorization.  The Diameter
   <xref target="RFC7155"/> is implemented in the Network Access Server (NAS).
</t>
<t>
   The user logs on to the network (1).  The Diameter NAS sends a
   Diameter AA-Request to the home Diameter AAA server.  The credit-control
   client populates the AAR with the Credit-Control AVP set to
   CREDIT_AUTHORIZATION, and service-specific AVPs are included, as
   usual <xref target="RFC7155"/>.  The home Diameter AAA server performs service-specific 
   Authentication and Authorization, as usual.  The home
   Diameter AAA server determines that the user has a prepaid
   subscription and notices from the Credit-Control AVP that the NAS has
   credit-control capabilities.  It sends a Diameter Credit-Control-Request
   with CC-Request-Type set to INITIAL_REQUEST to the Diameter
   credit-control server to perform credit authorization (3) and to
   establish a credit-control session.  (The home Diameter AAA server
   may forward service-specific AVPs received from the NAS as input for
   the rating process.)  The Diameter credit-control server checks the
   end user's account balance, determines that the account cannot cover
   the cost of the service, and initiates the graceful service
   termination.  The Credit-Control-Answer is returned to the home
   Diameter AAA server (4).  This message contains the Final-Unit-Indication
   AVP and the Validity-Time AVP set to a reasonable amount
   of time to give the user a chance to replenish his/her account (e.g.,
   10 minutes).  The Final-Unit-Indication AVP includes the Final-Unit-Action
   set to REDIRECT, the Redirect-Address-Type set to URL, and the
   Redirect-Server-Address set to the HTTP Top-up server name.  The home
   Diameter AAA server sends the received credit-control AVPs to the NAS
   in the Diameter AA-Answer (5).  Upon successful AAA, the NAS starts
   the credit-control session and immediately starts the graceful
   service termination, as instructed by the server.  The NAS grants
   limited access to the user (6).  The HTTP client software running in
   the user's device opens the transport connection redirected by the
   NAS to the Top-up server (7,8).  The user is displayed an appropriate
   web page on which to enter the credit card number, and the amount of
   money to be used to replenish the account, and with a notification
   message that she is granted unlimited access if the replenishment
   operation will be successfully executed within the next, for example,
   10 minutes.  The Top-up server validates the credit card number and
   replenishes the user's account (using some means outside the scope of
   this specification)(9).  After successful account top-up, the
   credit-control server sends a Re-Auth-Request message to the NAS
   (10).  The NAS acknowledges the request by returning the Re-Auth-Answer
   message (11) and initiates the credit re-authorization by
   sending a Credit-Control-request (UPDATE_REQUEST) to the Diameter
   credit-control server (12,13).
</t>
<t>
   The Diameter credit-control server reserves credit from the end
   user's account and returns the reserved quota to the NAS via the home
   Diameter AAA server in the Credit-Control-Answer (14,15).  The NAS
   removes the restriction placed by the graceful service termination
   and starts monitoring the granted units.
</t>
  </section>
  <section anchor="app-a9" title="Flow IX">
<t>
   The Diameter credit-control application defines the Multiple-Services-Credit-Control
   AVP that can be used to support independent
   credit-control of multiple services in a single credit-control (sub-)
   session for service elements that have such capabilities.  It is
   possible to request and allocate resources as a credit pool that is
   shared between services or rating groups.
</t>
<t>
   The flow example hereafter illustrates a usage scenario where the
   credit-control client and server support independent credit-control
   of multiple services, as defined in <xref target="sec-5.1.2"/>.  It is assumed
   that Service-Identifiers, Rating-Groups, and their associated
   parameters (e.g., IP 5-tuple) are locally configured in the service
   element or provisioned by an entity other than the credit-control
   server.
</t>
<figure anchor="flow9" title="Flow example independent credit-control of multiple services in a  credit-control (sub-)Session">
<artwork><![CDATA[
End User         Service Element                           CC Server
                   (CC client)
  |(1)User logon      |                                         |
  |------------------>|(2)CCR(initial, Service-Id access,       |
  |                   |        Access-specific AVPs,            |
  |                   |        Multiple-Service-Indicator)      |
  |                   |---------------------------------------->|
  |                   |(3)CCA(Multiple-Services-CC (            |
  |                   |        Granted-Units(Total-Octets),     |
  |                   |        Service-Id access,               |
  |                   |        Validity-time,                   |
  |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
  |                   |          Multiplier 10)))               |
  |                   |<----------------------------------------|
  :                   :                                         :
  |(4)Service-Request (Service 1)                               |
  |------------------>|(5)CCR(update, Multiple-Services-CC(     |
  |                   |        Requested-Units(), Service-Id 1, |
  |                   |        Rating-Group 1))                 |
  |                   |---------------------------------------->|
  |                   |(6)CCA(Multiple-Services-CC (            |
  |                   |        Granted-Units(Time),             |
  |                   |        Rating-Group 1,                  |
  |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
  |                   |          Multiplier 1)))                |
  |                   |<----------------------------------------|
  :                   :                                         :
  |(7)Service-Request (Service 2)                               |
  |------------------>|                                         |
  :                   :                                         :
  :                   :                                         :
  |(8)Service-Request (Service 3&4)                             |
  |------------------>|(9)CCR(update, Multiple-Services-CC (    |
  |                   |        Requested-Units(), Service-Id 3, |
  |                   |        Rating-Group 2),                 |
  |                   |        Multiple-Services-CC (           |
  |                   |        Requested-Units(), Service-Id 4, |
  |                   |        Rating-Group 3))                 |
  |                   |---------------------------------------->|
  |                   |(10)CCA(Multiple-Services-CC (           |
  |                   |        Granted-Units(Total-Octets),     |
  |                   |        Service-Id 3, Rating-Group 2,    |
  |                   |        Validity-time,                   |
  |                   |        G-S-U-Pool-Reference(Pool-Id 2,  |
  |                   |          Multiplier 2)),                |
  |                   |        Multiple-Services-CC (           |
  |                   |        Granted-Units(Total-Octets),     |
  |                   |        Service-Id 4, Rating-Group 3     |
  |                   |        Validity-Time,                   |
  |                   |        Final-Unit-Ind.(Terminate),      |
  |                   |        G-S-U-Pool-Reference(Pool-Id 2,  |
  |                   |          Multiplier 5)))                |
  |                   |<----------------------------------------|
  :                   :                                         :
  :                   :                                         :
  | +--------------+  |                                         |
  | |Validity time |  |(11)CCR(update,                          |
  | |expires for   |  |        Multiple-Services-CC (           |
  | |Service-Id    |  |        Requested-Unit(),                |
  | | access       |  |        Used-Units(In-Octets,Out-Octets),|
  | +--------------+  |        Service-Id access))              |
  |                   |---------------------------------------->|
  |                   |(12)CCA(Multiple-Services-CC (           |
  |                   |        Granted-Units(Total-Octets),     |
  |                   |        Service-Id access,               |
  |                   |        Validity-Time,                   |
  |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
  |                   |          Multiplier 10)))               |
  |                   |<----------------------------------------|
  :                   :                                         :
  :                   :                                         :
  | +--------------+  |                                         |
  | |Total Quota   |  |(13)CCR(update,                          |
  | |elapses for   |  |       Multiple-Services-CC (            |
  | |pool 2:       |  |        Requested-Unit(),                |
  | |service 4 not |  |        Used-Units(In-Octets,Out-Octets),|
  | |allowed,      |  |        Service-Id 3, Rating-group 2),   |
  | |service 3 cont|  |       Multiple-Services-CC (            |
  | +--------------+  |        Used-Units(In-Octets,Out-Octets),|
  |                   |        Service-Id 4, Rating-Group 3))   |
  |                   |---------------------------------------->|
  |                   |(14)CCA(Multiple-Services-CC (           |
  |                   |        Result-Code 4011,                |
  |                   |        Service-Id 3))                   |
  |                   |<----------------------------------------|
  :                   :                                         :
  :                   :                                         :
  |(15) User logoff   |                                         |
  |------------------>|(16)CCR(term,                            |
  |                   |       Multiple-Services-CC (            |
  |                   |        Used-Units(In-Octets,Out-Octets),|
  |                   |        Service-Id access),              |
  |                   |       Multiple-Services-CC (            |
  |                   |        Used-Units(Time),                |
  |                   |        Service-Id 1, Rating-Group 1),   |
  |                   |       Multiple-Services-CC (            |
  |                   |        Used-Units(Time),                |
  |                   |        Service-Id 2, Rating-Group 1))   |
  |                   |---------------------------------------->|
  |                   |(17)CCA(term)                            |
  |                   |<----------------------------------------|
]]></artwork>
    </figure>
<t>
   The user logs on to the network (1).  The service element sends a
   Diameter Credit-Control-Request with CC-Request-Type set to
   INITIAL_REQUEST to the Diameter credit-control server to perform
   credit authorization for the bearer service (e.g., Internet access
   service) and to establish a credit-control session (2).  In this
   message, the credit-control client indicates support for independent
   credit-control of multiple services within the session by including
   the Multiple-Service-Indicator AVP.  The Diameter credit-control
   server checks the end user's account balance, with rating information
   received from the client (i.e., Service-Id and access-specific AVPs),
   rates the request, and reserves credit from the end user's account.
   Suppose that the server reserves $5 and determines that the cost is
   $1/MB.  It then returns to the service element a Credit-Control-Answer
   message that includes the Multiple-Services-Credit-Control AVP
   with a quota of 5MB associated to the Service-Id (access), to a
   multiplier value of 10, and to the Pool-Id 1 (3).
</t>
<t>
   The user uses Service 1 (4).  The service element sends a Diameter
   Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to
   the credit-control server to perform credit authorization for service
   1 (5).  This message includes the Multiple-Services-Credit-Control
   AVP to request service units for Service 1 that belong to Rating-Group
   1.  The Diameter credit-control server determines that Service
   1 draws credit resources from the same account as the access service
   (i.e., pool 1).  It rates the request according to Service-Id/Rating-Group
   and updates the existing reservation by requesting
   more credit.  Suppose that the server reserves $5 more (now the
   reservation is $10) and determines that the cost is $0.1/minute.  The
   server authorizes the whole Rating-Group.  It then returns to the
   service element a Credit-Control-Answer message that includes the
   Multiple-Services-Credit-Control AVP with a quota of 50min.
   associated to the Rating-Group 1, to a multiplier value of 1, and to
   the Pool-Id 1 (6).  The client adjusts the total amount of resources
   for pool 1 according the received quota, which gives S for Pool 1 =
   100.
</t>
<t>
   The user uses Service 2, which belongs to the authorized
   Rating-Group, 1 (7).  Resources are then consumed from the pool 1.
</t>
<t>
   The user now requests Services 3 and 4 as well, which are not
   authorized (8).  The service element sends a Diameter
   Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to the
   credit-control server in order to perform credit authorization for
   Services 3 and 4 (9).  This message includes two instances of the
   Multiple-Services-Credit-Control AVP to request service units for
   Service 3 that belong to Rating-Group 2 and for Service 4 that belong
   to Rating-Group 3.  The Diameter credit-control server determines
   that Services 3 and 4 draw credit resources from another account
   (i.e., pool 2).  It checks the end user's account balance and,
   according to Service-Ids/Rating-Groups information, rates the
   request.  Then it reserves credit from pool 2.
</t>
<t>
   For example, the server reserves $5 and determines that Service 3
   costs $0.2/MB and Service 4 costs $0.5/MB.  The server authorizes
   only Services 3 and 4.  It returns to the service element a
   Credit-Control-Answer message that includes two instances of the
   Multiple-Services-Credit-Control AVP (10).  One instance grants a quota of
   12.5MB associated to the Service-Id 3 to a multiplier value of 2 and
   to the Pool-Id 2.  The other instance grants a quota of 5 MB
   associated to the Service-Id 4 to a multiplier value of 5 and to the
   Pool-Id 2.
</t>
<t>
   The server also determines that pool 2 is exhausted and Service 4 is
   not allowed to continue after these units will be consumed.
   Therefore the Final-Unit-Indication AVP with action TERMINATE is
   associated to the Service-Id 4.  The client calculates the total
   amount of resources that can be used for pool 2 according the
   received quotas and multipliers, which gives S for Pool 2 = 50.
</t>
<t>
   The Validity-Time for the access service expires.  The service
   element sends a Credit-Control-Request message to the server in order
   to perform credit re-authorization for Service-Id (access) (11).
   This message carries one instance of the Multiple-Services-Credit-Control
   AVP that includes the units used by this service.  Suppose
   that the total amount of used units is 4MB.  The client adjusts the
   total amount of resources for pool 1 accordingly, which gives S for
   Pool 1 = 60.
</t>
<t>
   The server deducts $4 from the user's account and updates the
   reservation by requesting more credit.  Suppose that the server
   reserves $5 more (now the reservation is $11) and already knows the
   cost of the Service-Id (access), which is $1/MB.  It then returns to
   the service element a Credit-Control-Answer message that includes the
   Multiple-Services-Credit-Control AVP with a quota of 5 MB associated
   to the Service-Id (access), to a multiplier value of 10, and to the
   Pool-Id 1 (12).  The client adjusts the total amount of resources for
   pool 1 according the received quota, which gives S for Pool 1 = 110.
</t>
<t>
   Services 3 and 4 consume the total amount of pool 2 credit resources
   (i.e., C1*2 + C2*5 >= S).  The service element immediately starts the
   TERMINATE action concerning Service 4 and sends a Credit-Control-Request
   message with CC-Request-Type set to UPDATE_REQUEST to the
   credit-control server in order to perform credit re-authorization for
   Service 3 (13).  This message contains two instances of the
   Multiple-Services-Credit-Control AVP to report the units used by
   Services 3 and 4.  The server deducts the last $5 from the user's
   account (pool 2) and returns the answer with Result-Code 4011 in the
   Multiple-Services-Credit-Control AVP to indicate that Service 3 can
   continue without credit-control (14).
</t>
<t>
   The end user logs off from the network (15).  To debit the used units
   from the end user's account and to stop the credit-control session,
   the service element sends a Diameter Credit-Control-Request with
   CC-Request-Type set to TERMINATION_REQUEST to the credit-control server
   (16).  This message contains the units consumed by each of the used
   services in multiple instances of the Multiple-Services-Credit-Control
   AVP.  The used units are associated with the relevant
   Service-Identifier and Rating-Group.  The Diameter credit-control
   server debits the used units to the user's account (Pool 1) and
   acknowledges the session termination by sending a Diameter
   Credit-Control-Answer to the service element (17).
</t>
  </section>
</section>

<section title="Changes relative to RFC4006">
  <t>The following changes were made relative to RFC4006:
  <list>
    <t>Update references to obsolete RFC 3588 to refer to RFC 6733.</t>
    <t>Update references to obsolete RFC 4005 to refer to RFC 7155.</t>
    <t>Update references to obsolete RFC 2486 to refer to RFC 7542.</t>
    <t>Update references to current 3GPP documents.</t>
    <t>Update AVP per Errata ID 3329.</t>
    <t>Update reference to "IPsec or TLS" to be "TLS/TCP, DTLS/SCTP or IPsec".</t>
    <t>Clarify Filter-Rule AVP in Restrict Access Action.</t>
    <t>Remove Encr column from AVP flag rules.</t>
    <t>Clarify that RESTRICT_ACCESS action applies after consumption of final granted units (<xref target="sec-5.6.3"/>).</t>
    <t>Clarify that values in Used-Service-Unit AVP may exceed Granted-Service-Unit AVP (<xref target="sec-8.19"/>).</t>
    <t>Clarify that IPv6 representation in Redirect-Address-Type AVP conforms to RFC5952 (<xref target="sec-8.38"/>).</t>
    <t>Describe immediate graceful service termination procedure (in <xref target="sec-5.6"/>).</t>
    <t>Add extensible User-Equipment-Info-Extension AVP and included types (from <xref target="sec-8.52"/> to <xref target="sec-8.57"/>).</t>
    <t>Define binary MAC formatting in User-Equipment-Info-MAC instead of the textual formatting in User-Equipment-Info-Data when type is MAC.</t>
    <t>Add extensible Subscription-Id-Extension AVP and included types (from <xref target="sec-8.58"/> to <xref target="sec-8.63"/>).</t>
    <t>Add extensible Redirect-Server-Extension AVP and included types (from <xref target="sec-8.64"/> to <xref target="sec-8.67"/>).</t>
    <t>Add extensible QoS-Final-Unit-Indication AVP (in <xref target="sec-8.68"/>).</t>
    <t>Updated Security Section to include language consistent with structures of latest base protocol specification.</t>
    <t>Update references to obsolete RFC 5226 to refer to RFC 8126, and resulting updates to <xref target="sec-12"/>.</t>
    <t>Add section on Privacy Considerations.</t>
    <t>Language updated from RFC 2119 updated to RFC 8174.</t>
  </list>
  </t>
</section>
 </back>
</rfc>