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RFC 4740

 
 
 

Diameter Session Initiation Protocol (SIP) Application

Part 2 of 4, p. 21 to 43
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7.  Advertising Application Support

   Diameter implementations conforming to this specification MUST
   advertise its support by including an Auth-Application-Id AVP in the
   Capabilities-Exchange-Request (CER) and Capabilities-Exchange-Answer
   (CEA) commands, according to the Diameter base protocol, RFC 3588
   [RFC3588].  This Auth-Application-Id AVP MUST be set to the value of
   this Diameter SIP application (Section 13.1 indicates the actual
   value allocated by IANA).

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8.  Diameter SIP Application Command Codes

   All the Diameter implementations conforming to this specification
   MUST implement and support the list of Diameter commands listed in
   Table 1.

   +-------------------------------------+-------+------+--------------+
   | Command Name                        | Abbr. | Code | Reference    |
   +-------------------------------------+-------+------+--------------+
   | User-Authorization-Request          |  UAR  |  283 | Section 8.1  |
   | User-Authorization-Answer           |  UAA  |  283 | Section 8.2  |
   | Server-Assignment-Request           |  SAR  |  284 | Section 8.3  |
   | Server-Assignment-Answer            |  SAA  |  284 | Section 8.4  |
   | Location-Info-Request               |  LIR  |  285 | Section 8.5  |
   | Location-Info-Answer                |  LIA  |  285 | Section 8.6  |
   | Multimedia-Auth-Request             |  MAR  |  286 | Section 8.7  |
   | Multimedia-Auth-Answer              |  MAA  |  286 | Section 8.8  |
   | Registration-Termination-Request    |  RTR  |  287 | Section 8.9  |
   | Registration-Termination-Answer     |  RTA  |  287 | Section 8.10 |
   | Push-Profile-Request                |  PPR  |  288 | Section 8.11 |
   | Push-Profile-Answer                 |  PPA  |  288 | Section 8.12 |
   +-------------------------------------+-------+------+--------------+

                      Table 1: Defined command codes

   Sections defining commands contain the Message Format for that
   particular command.  The Message Formats included in this document
   are defined as per Section 3.2 of RFC 3588 [RFC3588].

8.1.  User-Authorization-Request (UAR) Command

   The User-Authorization-Request (UAR) is indicated by the Command-Code
   set to 283 and the Command Flags' 'R' bit set.  The Diameter client
   in a SIP server sends this command to the Diameter server to request
   authorization for the SIP User Agent to route a SIP REGISTER request.
   Because the SIP REGISTER request implicitly carries a permission to
   bind an AOR to a contact address, the Diameter client uses the
   Diameter UAR as a first authorization request towards the Diameter
   server to authorize the registration.  For instance, the Diameter
   server can verify that the AOR is a legitimate user of the realm.

   The Diameter client in the SIP server requests authorization for one
   of the possible values defined in the SIP-User-Authorization-Type AVP
   (Section 9.10).

   The user name used for authentication of the user is conveyed in a
   User-Name AVP (defined in the Diameter base protocol, RFC 3588
   [RFC3588]).  The location of the authentication user name in the SIP

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   REGISTER request varies depending on the authentication mechanism.
   When the authentication mechanism is HTTP Digest as defined in RFC
   2617 [RFC2617], the authentication user name is found in the
   "username" directive of the SIP Authorization header field value.
   This Diameter SIP application only provides support for HTTP Digest
   authentication in SIP; other authentication mechanisms are not
   currently supported.

   The SIP or SIPS URI to be registered is conveyed in the SIP-AOR AVP
   (Section 9.8).  Typically this SIP or SIPS URI is found in the To
   header field value of the SIP REGISTER request that triggered the
   Diameter UAR message.

   The SIP-Visited-Network-Id AVP indicates the network that is
   providing SIP services (e.g., SIP proxy functionality or any other
   kind of services) to the SIP User Agent.

   The Message Format of the UAR command is as follows:

       <UAR> ::= < Diameter Header: 283, REQ, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { SIP-AOR }
                 [ Destination-Host ]
                 [ User-Name ]
                 [ SIP-Visited-Network-Id ]
                 [ SIP-User-Authorization-Type ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.2.  User-Authorization-Answer (UAA) Command

   The User-Authorization-Answer (UAA) is indicated by the Command-Code
   set to 283 and the Command Flags' 'R' bit cleared.  The Diameter
   server sends this command in response to a previously received
   Diameter User-Authorization-Request (UAR) command.  The Diameter
   server indicates the result of the requested registration
   authorization.  Additionally, the Diameter server may indicate a
   collection of SIP capabilities that assists the Diameter client to
   select a SIP proxy to the AOR under registration.

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   In addition to the values already defined in RFC 3588 [RFC3588], the
   Result-Code AVP may contain one of the values defined in
   Section 10.1.

   Whenever the Diameter server fails to process the Diameter UAR
   message, it MUST stop processing and return the relevant error in the
   Diameter UAA message.  When there is success in the process, the
   Diameter server MUST set the code to DIAMETER_SUCCESS in the Diameter
   UAA message.

   If the Diameter server requires a User-Name AVP value to process the
   Diameter UAR request, but the Diameter UAR message did not contain a
   User-Name AVP value, the Diameter server MUST set the Result-Code AVP
   value to DIAMETER_USER_NAME_REQUIRED (see Section 10.1.2) and return
   it in a Diameter UAA message.  Upon reception of this Diameter UAA
   message with the Result-Code AVP value set to
   DIAMETER_USER_NAME_REQUIRED, the SIP server typically requests
   authentication by sending a SIP 401 (Unauthorized) or SIP 407 (Proxy
   Authentication Required) response back to the originator.

   When the authorization procedure succeeds, the Diameter server
   constructs a User-Authorization-Answer (UAA) message that MUST
   include (1) the address of the SIP server already assigned to the
   user name, (2) the capabilities needed by the SIP server (Diameter
   client) to select another SIP server for the user, or (3) a
   combination of the previous two options.

   If the Diameter server is already aware of a SIP server allocated to
   the user, the Diameter UAA message contains the address of that SIP
   server.

   The Diameter UAA message contains the capabilities required by a SIP
   server to trigger and execute services.  It is required that these
   capabilities are present in the Diameter UAA message due to the
   possibility that the Diameter client (in the SIP server) allocates a
   different SIP server to trigger and execute services for that
   particular user.

   If a User-Name AVP is present in the Diameter UAR message, then the
   Diameter server MUST verify the existence of the user in the realm,
   i.e., the User-Name AVP value is a valid user within that realm.  If
   the Diameter server does not recognize the user name received in the
   User-Name AVP, the Diameter server MUST build a Diameter User-
   Authorization-Answer (UAA) message and MUST set the Result-Code AVP
   to DIAMETER_ERROR_USER_UNKNOWN.

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   If a User-Name AVP is present in the Diameter UAR message, then the
   Diameter server MUST authorize that User-Name AVP value is able to
   register the SIP or SIPS URI included in the SIP-AOR AVP.  If this
   authorization fails, the Diameter server must set the Result-Code AVP
   to DIAMETER_ERROR_IDENTITIES_DONT_MATCH and send it in a Diameter
   User-Authorization-Answer (UAA) message.

      Note: Correlation between User-Name and SIP-AOR AVP values is
      required in order to avoid registration of a SIP-AOR allocated to
      another user.

   If there is a SIP-Visited-Network-Id AVP in the Diameter UAR message,
   and the SIP-User-Authorization-Type AVP value received in the
   Diameter UAR message is set to REGISTRATION or REGISTRATION&
   CAPABILITIES, then the Diameter server SHOULD verify whether the user
   is allowed to roam into the network specified in the
   SIP-Visited-Network-Id AVP in the Diameter UAR message.  If the user
   is not allowed to roam into that network, the Diameter AAA server
   MUST set the Result-Code AVP value in the Diameter UAA message to
   DIAMETER_ERROR_ROAMING_NOT_ALLOWED.

   If the SIP-User-Authorization-Type AVP value received in the Diameter
   UAR message is set to REGISTRATION or REGISTRATION&CAPABILITIES, then
   the Diameter server SHOULD verify whether the SIP-AOR AVP value is
   authorized to register in the Home Realm.  Where the SIP AOR is not
   authorized to register in the Home Realm, the Diameter server MUST
   set the Result-Code AVP to DIAMETER_AUTHORIZATION_REJECTED and send
   it in a Diameter UAA message.

   When the SIP-User-Authorization-Type AVP is not present in the
   Diameter UAR message, or when it is present and its value is set to
   REGISTRATION, then:

   o  If the Diameter server is not aware of any previous registration
      of the user name (including registrations of other SIP AORs
      allocated to the same user name), then the Diameter server does
      not know of any SIP server allocated to the user.  In this case,
      the Diameter server MUST set the Result-Code AVP value to
      DIAMETER_FIRST_REGISTRATION in the Diameter UAA message, and the
      Diameter server SHOULD include the required SIP server
      capabilities in the SIP-Server-Capabilities AVP value in the
      Diameter UAA message.  The SIP-Server-Capabilities AVP assists the
      Diameter client (SIP server) to select an appropriate SIP server
      for the user, according to the required capabilities.

   o  In some cases, the Diameter server is aware of a previously
      assigned SIP server for the same or different SIP AORs allocated
      to the same user name.  In these cases, re-assignment of a new SIP

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      server may or may not be needed, depending on the capabilities of
      the SIP server.  The Diameter server MUST always include the
      allocated SIP server URI in the SIP-Server-URI AVP of the UAA
      message.  If the Diameter server does not return the SIP
      capabilities, the Diameter server MUST set the Result-Code AVP in
      the Diameter UAA message to DIAMETER_SUBSEQUENT_REGISTRATION.
      Otherwise (i.e., if the Diameter server includes a
      SIP-Server-Capabilities AVP), then the Diameter server MUST set
      the Result-Code AVP in the Diameter UAA message to
      DIAMETER_SERVER_SELECTION.  Then the Diameter client determines,
      based on the received information, whether it needs to select a
      new SIP server.

   When the SIP-User-Authorization-Type AVP value received in the
   Diameter UAR message is set to REGISTRATION&CAPABILITIES, then
   Diameter Server MUST return the list of capabilities in the
   SIP-Server-Capabilities AVP value of the Diameter UAA message, it
   MUST set the Result-Code to DIAMETER_SUCCESS, and it MUST NOT return
   a SIP-Server-URI AVP.  The SIP-Server-Capabilities AVP enables the
   SIP server (Diameter client) to select another appropriate SIP server
   for invoking and executing services for the user, depending on the
   required capabilities.  The Diameter server MAY leave the list of
   capabilities empty to indicate that any SIP server can be selected.

   When the SIP-User-Authorization-Type AVP value received in the
   Diameter UAR message is set to DEREGISTRATION, then:

   o  If the Diameter server is aware of a SIP server assigned to the
      SIP AOR under deregistration, the Diameter server MUST set the
      Result-Code AVP to DIAMETER_SUCCESS and MUST set the
      SIP-Server-URI AVP value to the known SIP server, and return them
      in the Diameter UAA message.

   o  If the Diameter server is not aware of a SIP server assigned to
      the SIP AOR under deregistration, then the Diameter server MUST
      set the Result-Code AVP in the Diameter UAA message to
      DIAMETER_ERROR_IDENTITY_NOT_REGISTERED.

   The Message Format of the UAA command is as follows:

       <UAA> ::= < Diameter Header: 283, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Result-Code }
                 { Origin-Host }
                 { Origin-Realm }
                 [ SIP-Server-URI ]

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                 [ SIP-Server-Capabilities ]
                 [ Authorization-Lifetime ]
                 [ Auth-Grace-Period ]
                 [ Redirect-Host ]
                 [ Redirect-Host-Usage ]
                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.3.  Server-Assignment-Request (SAR) Command

   The Server-Assignment-Request (SAR) command is indicated by the
   Command-Code set to 284 and the Command Flags' 'R' bit set.  The
   Diameter client in a SIP server sends this command to the Diameter
   server to indicate the completion of the authentication process and
   to request that the Diameter server store the URI of the SIP server
   that is currently serving the user.  The main functions of the
   Diameter SAR command are to inform the Diameter server of the URI of
   the SIP server allocated to the user, and to store or clear it from
   the Diameter server.  Additionally, the Diameter client can request
   to download the user profile or part of it.

   During the registration procedure, a SIP server becomes assigned to
   the user.  The Diameter client in the assigned SIP server MUST
   include its own URI in the SIP-Server-URI AVP of the
   Server-Assignment-Request (SAR) Diameter message and send it to the
   Diameter server.  The Diameter server then becomes aware of the
   allocation of the SIP server to the user name and the server's URI.

   The Diameter client in the SIP server MAY send a Diameter SAR message
   because of other reasons.  These reasons are identified in the
   SIP-Server-Assignment-Type AVP (Section 9.4) value.  For instance, a
   Diameter client in a SIP server may contact the Diameter server to
   request deregistration of a user, to inform the Diameter server of an
   authentication failure, or just to download the user profile.  For a
   complete description of all the SIP-Server-Assignment-Type AVP
   values, see Section 9.4.

   Typically the reception of a SIP REGISTER request in a SIP server
   will trigger the Diameter client in the SIP server to send the
   Diameter SAR message.  However, if a SIP server is receiving other
   SIP request, such as INVITE, and the SIP server does not have the
   user profile, the Diameter client in the SIP server may send the
   Diameter SAR message to the Diameter server in order to download the
   user profile and make the Diameter server aware of the SIP server
   assigned to the user.

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   The user profile is an important piece of information that dictates
   the behavior of the SIP server when triggering or providing services
   for the user.  Typically the user profile is divided into:

   o  Services to be rendered to the user when the user is registered
      and initiates a SIP request.

   o  Services to be rendered to the user when the user is registered
      and a SIP request destined to that user arrives to the SIP proxy.

   o  Services to be rendered to the user when the user is not
      registered and a SIP request destined to that user arrives to the
      SIP proxy.

   The SIP-Server-Assignment-Type AVP indicates the reason why the
   Diameter client (SIP server) contacted the Diameter server.  If the
   Diameter client sets the SIP-Server-Assignment-Type AVP value to
   REGISTRATION, RE_REGISTRATION, UNREGISTERED_USER, NO_ASSIGNMENT,
   AUTHENTICATION_FAILURE or AUTHENTICATION_TIMEOUT, the Diameter client
   MUST include exactly one SIP-AOR AVP in the Diameter SAR message.

   The SAR message MAY contain zero or more SIP-Supported-User-Data-Type
   AVPs.  Each of them contains a type of user data understood by the
   SIP server.  This allows the Diameter client to provide an indication
   to the Diameter server of the different format of user data
   understood by the SIP server.  The Diameter server uses this
   information to select one or more SIP-User-Data AVPs that will be
   included in the SAA message.

   The Message Format of the SAR command is as follows:

       <SAR> ::= < Diameter Header: 284, REQ, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { SIP-Server-Assignment-Type }
                 { SIP-User-Data-Already-Available }
                 [ Destination-Host ]
                 [ User-Name ]
                 [ SIP-Server-URI ]
               * [ SIP-Supported-User-Data-Type ]
               * [ SIP-AOR ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

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8.4.  Server-Assignment-Answer (SAA) Command

   The Server-Assignment-Answer (SAA) is indicated by the Command-Code
   set to 284 and the Command Flags' 'R' bit cleared.  The Diameter
   server sends this command in response to a previously received
   Diameter Server-Assignment-Request (SAR) command.  The response may
   include the user profile or part of it, if requested.

   In addition to the values already defined in RFC 3588 [RFC3588], the
   Result-Code AVP may contain one of the values defined in
   Section 10.1.

   The Result-Code AVP value in the Diameter SAA message may indicate a
   success or an error in the execution of the Diameter SAR command.  If
   Result-Code AVP value in the Diameter SAA message does not contain an
   error code, the SAA message MAY include one or more SIP-User-Data
   AVPs that typically contain the profile of the user, indicating
   services that the SIP server can provide to that user.

   The Diameter server MAY include one or more
   SIP-Supported-User-Data-Type AVPs, each one identifying a type of
   user data format supported in the Diameter server.  If there is not a
   common supported user data type between the Diameter client and the
   Diameter server, the Diameter server SHOULD declare its list of
   supported user data types by including one or more
   SIP-Supported-User-Data-Type AVPs in a Diameter SAA message.  This
   indication is merely for debugging reasons, since there is not a
   fallback mechanism that allows the Diameter client to retrieve the
   profile in a supported format.

   If the Diameter server requires a User-Name AVP value to process the
   Diameter SAR request, but the Diameter SAR message did not contain a
   User-Name AVP value, the Diameter server MUST set the Result-Code AVP
   value to DIAMETER_USER_NAME_REQUIRED (see Section 10.1.2) and return
   it in a Diameter SAA message.  Upon reception of this Diameter SAA
   message with the Result-Code AVP value set to
   DIAMETER_USER_NAME_REQUIRED, the SIP server typically requests
   authentication by generating a SIP 401 (Unauthorized) or SIP 407
   (Proxy Authentication Required) response back to the originator.

   If the User-Name AVP is included in the Diameter SAR message, upon
   reception of the Diameter SAR message, the Diameter server MUST
   verify the existence of the user in the realm, i.e., the User-Name
   AVP value is a valid user within that realm.  If the Diameter server
   does not recognize the user name received in the User-Name AVP, the
   Diameter server MUST build a Diameter Server-Assignment-Answer (SAA)
   message and MUST set the Result-Code AVP to
   DIAMETER_ERROR_USER_UNKNOWN.

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   Then the Diameter server MUST authorize that User-Name AVP value is a
   valid authentication name for the SIP or SIPS URI included in the
   SIP-AOR AVP of the Diameter SAR message.  If this authorization
   fails, the Diameter server must set the Result-Code AVP to
   DIAMETER_ERROR_IDENTITIES_DONT_MATCH and send it in a Diameter
   Server-Assignment-Answer (SAA) message.

   After successful execution of the Diameter SAR command, the Diameter
   server MUST clear the "authentication pending" flag and SHOULD move
   the temporarily stored SIP server URI to permanent storage.

   The actions of the Diameter server upon reception of the Diameter SAR
   message depend on the value of the SIP-Server-Assignment-Type:

   o  If the SIP-Server-Assignment-Type AVP value in the Diameter SAR
      message is set to REGISTRATION or RE_REGISTRATION, the Diameter
      server SHOULD verify that there is only one SIP-AOR AVP.
      Otherwise, the Diameter server MUST answer with a Diameter SAA
      message with the Result-Code AVP value set to
      DIAMETER_AVP_OCCURS_TOO_MANY_TIMES and MUST NOT include any
      SIP-User-Data AVP.  If there is only one SIP-AOR AVP and if the
      SIP-User-Data-Already-Available AVP value is set to
      USER_DATA_NOT_AVAILABLE, then the Diameter server SHOULD include
      one or more user profile data with the SIP or SIPS URI (SIP-AOR
      AVP) and all other SIP identities associated with that AVP in the
      SIP-User-Data AVP value of the Diameter SAA message.  On selecting
      the type of user data, the Diameter server SHOULD take into
      account the supported formats at the SIP server
      (SIP-Supported-User-Data-Type AVP in the SAR message) and the
      local policy.  Additionally, the Diameter server MUST set the
      Result-Code AVP value to DIAMETER_SUCCESS in the Diameter SAA
      message.  The Diameter server considers the SIP AOR authenticated
      and registered.

   o  If the SIP-Server-Assignment-Type AVP value in the Diameter SAR
      message is set to UNREGISTERED_USER, then the Diameter server MUST
      store the SIP server address included in the SIP-Server-URI AVP
      value.  The Diameter server will return the SIP server address in
      Diameter Location-Info-Answer (LIA) messages.  If the
      SIP-User-Data-Already-Available AVP value is set to
      USER_DATA_NOT_AVAILABLE, then the Diameter server SHOULD include
      one or more user profile data associated with the SIP or SIPS URI
      (SIP-AOR AVP) and associated identities in the SIP-User-Data AVP
      value of the Diameter SAA message.  On selecting the type of user
      data, the Diameter server SHOULD take into account the supported
      formats at the SIP server (SIP-Supported-User-Data-Type AVP in the
      SAR message) and the local policy.  The Diameter server MUST set
      the Result-Code AVP value to DIAMETER_SUCCESS.  The Diameter

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      server considers the SIP AOR UNREGISTERED, but with a SIP server
      allocated to trigger and provide services for unregistered users.
      Note that in case of UNREGISTERED_USER (SIP-Server-Assignment-Type
      AVP), the Diameter server MUST verify that there is only one
      SIP-AOR AVP.  Otherwise, the Diameter server MUST answer the
      Diameter SAR message with a Diameter SAA message, and it MUST set
      the Result-Code AVP value to DIAMETER_AVP_OCCURS_TOO_MANY_TIMES
      and MUST NOT include any SIP-User-Data AVP.
      If the User-Name AVP was not present in the Diameter SAR message
      and the SIP-AOR is not known for the Diameter server, the Diameter
      server MUST NOT include a User-Name AVP in the Diameter SAA
      message and MUST set the Result-Code AVP value to
      DIAMETER_ERROR_USER_UNKNOWN.

   o  If the SIP-Server-Assignment-Type AVP value in the Diameter SAR
      message is set to TIMEOUT_DEREGISTRATION, USER_DEREGISTRATION,
      DEREGISTRATION_TOO_MUCH_DATA, or ADMINISTRATIVE_DEREGISTRATION,
      the Diameter server MUST clear the SIP server address associated
      with all SIP AORs indicated in each of the SIP-AOR AVP values
      included in the Diameter SAR message.  The Diameter server
      considers all of these SIP AORs as not registered.  The Diameter
      server MUST set the Result-Code AVP value to DIAMETER_SUCCESS in
      the Diameter SAA message.

   o  If the SIP-Server-Assignment-Type AVP value in the Diameter SAR
      message is set to TIMEOUT_DEREGISTRATION_STORE_SERVER_NAME or
      USER_DEREGISTRATION_STORE_SERVER_NAME, the Diameter server MAY
      keep the SIP server address associated with the SIP AORs included
      in the SIP-AOR AVP values of the Diameter SAR message, even though
      the SIP AORs become unregistered.  This feature allows a SIP
      server to request that the Diameter server remain an assigned SIP
      server for those SIP AORs (SIP-AOR AVP values) allocated to the
      same user name, and avoid SIP server assignment.  The Diameter
      server MUST consider all these SIP AORs as not registered.  If the
      Diameter server honors the request of the Diameter client (SIP
      server) to remain as an allocated SIP server, then the Diameter
      server MUST keep the SIP server assigned to those SIP AORs
      allocated to the username and MUST set the Result-Code AVP value
      to DIAMETER_SUCCESS in the Diameter SAA message.  Otherwise, when
      the Diameter server does not honor the request of the Diameter
      client (SIP server) to remain as an allocated SIP server, the
      Diameter server MUST clear the SIP server name assigned to those
      SIP AORs and it MUST set the Result-Code AVP value to
      DIAMETER_SUCCESS_SERVER_NAME_NOT_STORED in the Diameter SAA
      message.

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   o  If the SIP-Server-Assignment-Type AVP value in the Diameter SAR
      message is set to NO_ASSIGNMENT, the Diameter server SHOULD first
      verify that the SIP-Server-URI AVP value in the Diameter SAR
      message is the same URI as the one assigned to the SIP-AOR AVP
      value.  If they differ, then the Diameter server MUST set the
      Result-Code AVP value to DIAMETER_UNABLE_TO_COMPLY in the Diameter
      SAA message.  Otherwise, if the SIP-User-Data-Already-Available
      AVP value is set to USER_DATA_NOT_AVAILABLE, then the Diameter
      server SHOULD include the user profile data with the SIP or SIPS
      URI (SIP-AOR AVP) and all other SIP identities associated with
      that AVP in the SIP-User-Data AVP value of the Diameter SAA
      message.  On selecting the type of user data, the Diameter server
      SHOULD take into account the supported formats at the SIP server
      (SIP-Supported-User-Data-Type AVP in the SAR message) and the
      local policy.

   o  If the SIP-Server-Assignment-Type AVP value in the Diameter SAR
      message is set to AUTHENTICATION_FAILURE or
      AUTHENTICATION_TIMEOUT, the Diameter server MUST verify that there
      is exactly one SIP-AOR AVP in the Diameter SAR message.  If the
      number of occurrences of the SIP-AOR AVP is not exactly one, the
      Diameter server MUST set the Result-Code AVP value to
      DIAMETER_AVP_OCCURS_TOO_MANY_TIMES in the Diameter SAA message,
      and SHOULD not take further actions.  If there is exactly one
      SIP-AOR AVP in the Diameter SAR message, the Diameter server MUST
      clear the address of the SIP server assigned to the SIP AOR
      allocated to the user name, and the Diameter server MUST set the
      Result-Code AVP value to DIAMETER_SUCCESS in the Diameter SAA
      message.  The Diameter server MUST consider the SIP AOR as not
      registered.

   The Message Format of the SAA command is as follows:

       <SAA> ::= < Diameter Header: 284, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Result-Code }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
               * [ SIP-User-Data ]
                 [ SIP-Accounting-Information ]
               * [ SIP-Supported-User-Data-Type ]
                 [ User-Name ]
                 [ Auth-Grace-Period ]
                 [ Authorization-Lifetime ]
                 [ Redirect-Host ]
                 [ Redirect-Host-Usage ]

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                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.5.  Location-Info-Request (LIR) Command

   The Location-Info-Request (LIR) is indicated by the Command-Code set
   to 285 and the Command Flags' 'R' bit set.  The Diameter client in a
   SIP server sends this command to the Diameter server to request
   routing information, e.g., the URI of the SIP server assigned to the
   SIP-AOR AVP value allocated to the users.

   The Message Format of the LIR command is as follows:

       <LIR> ::= < Diameter Header: 285, REQ, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { SIP-AOR }
                 [ Destination-Host ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.6.  Location-Info-Answer (LIA) Command

   The Location-Info-Answer (LIA) is indicated by the Command-Code set
   to 285 and the Command Flags' 'R' bit cleared.  The Diameter server
   sends this command in response to a previously received Diameter
   Location-Info-Request (LIR) command.

   In addition to the values already defined in RFC 3588 [RFC3588], the
   Result-Code AVP may contain one of the values defined in
   Section 10.1.  When the Diameter server finds an error in processing
   the Diameter LIR message, the Diameter server MUST stop the process
   of the message and answer with a Diameter LIA message that includes
   the appropriate error code in the Result-Code AVP value.  When there
   is no error, the Diameter server MUST set the Result-Code AVP value
   to DIAMETER_SUCCESS in the Diameter LIA message.

   One of the errors that the Diameter server may find is that the
   SIP-AOR AVP value is not a valid user in the realm.  In such cases,
   the Diameter server MUST set the Result-Code AVP value to
   DIAMETER_ERROR_USER_UNKNOWN and return it in a Diameter LIA message.

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   If the Diameter server cannot process the Diameter LIR command, e.g.,
   due to a database error, the Diameter server MUST set the Result-Code
   AVP value to DIAMETER_UNABLE_TO_COMPLY and return it in a Diameter
   LIA message.  The Diameter server MUST NOT include any SIP-Server-URI
   or SIP-Server-Capabilities AVP in the Diameter LIA message.

   The Diameter server may or may not be aware of a SIP server assigned
   to the SIP-AOR AVP value included in the Diameter LIR message.  If
   the Diameter server is aware of a SIP server allocated to that
   particular user, the Diameter server MUST include the URI of such SIP
   server in the SIP-Server-URI AVP and return it in a Diameter LIA
   message.  This is typically the situation when the user is either
   registered, or unregistered but a SIP server is still assigned to the
   user.

   When the Diameter server is not aware of a SIP server allocated to
   the user (typically the case when the user unregistered), the
   Result-Code AVP value in the Diameter LIA message depends on whether
   the Diameter server is aware that the user has services defined for
   unregistered users:

   o  Those users who have services defined for unregistered users may
      require the allocation of a SIP server to trigger and perhaps
      execute those services.  Therefore, when the Diameter server is
      not aware of an assigned SIP server, but the user has services
      defined for unregistered users, the Diameter server MUST set the
      Result-Code AVP value to DIAMETER_UNREGISTERED_SERVICE and return
      it in a Diameter LIA message.  The Diameter server MAY also
      include a SIP-Server-Capabilities AVP to facilitate the SIP server
      (Diameter client) with the selection of an appropriate SIP server
      with the required capabilities.  Absence of the SIP-Server-
      Capabilities AVP indicates to the SIP server (Diameter client)
      that any SIP server is suitable to be allocated for the user.

   o  Those users who do not have service defined for unregistered users
      do not require further processing.  The Diameter server MUST set
      the Result-Code AVP value to
      DIAMETER_ERROR_IDENTITY_NOT_REGISTERED and return it to the
      Diameter client in a Diameter LIA message.  The SIP server
      (Diameter client) may return the appropriate SIP response (e.g.,
      480 (Temporarily unavailable)) to the original SIP request.

   The Message Format of the LIA command is as follows:

       <LIA> ::= < Diameter Header: 285, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Result-Code }

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                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 [ SIP-Server-URI ]
                 [ SIP-Server-Capabilities ]
                 [ Auth-Grace-Period ]
                 [ Authorization-Lifetime ]
                 [ Redirect-Host ]
                 [ Redirect-Host-Usage ]
                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.7.  Multimedia-Auth-Request (MAR) Command

   The Multimedia-Auth-Request (MAR) command is indicated by the
   Command-Code set to 286 and the Command Flags' 'R' bit set.  The
   Diameter client in a SIP server sends this command to the Diameter
   server to request that the Diameter server authenticate and authorize
   a user attempt to use some SIP service (in this context, SIP service
   can be something as simple as a SIP subscription or using the proxy
   services for a SIP request).

   The MAR command may also register the SIP server's own URI to the
   Diameter server, so that future LIR/LIA messages can return this URI.
   If the SIP server is acting as a SIP registrar (see examples in
   Sections 6.2 and 6.3), its Diameter client MUST include a SIP-
   Server-URI AVP in the MAR command.  In any other cases (see example
   in Section 6.4), its Diameter client MUST NOT include a SIP-Server-
   URI AVP in the MAR command.

   The SIP-Method AVP MUST include the SIP method name of the SIP
   request that triggered this Diameter MAR message.  The Diameter
   server can use this AVP to authorize some SIP requests depending on
   the method.

   The Diameter MAR message MUST include a SIP-AOR AVP.  The SIP-AOR AVP
   indicates the target of the SIP request.  The value of the AVP is
   extracted from different places in SIP request, depending on the
   semantics of the SIP request.  For SIP REGISTER messages the SIP-AOR
   AVP value indicates the intended public user identity under
   registration, and it is the SIP or SIPS URI populated in the To
   header field value (addr-spec as per RFC 3261 [RFC3261]) of the SIP
   REGISTER request.  For other types of SIP requests, such as INVITE,
   SUBSCRIBE, MESSAGE, etc., the SIP-AOR AVP value indicates the
   intended destination of the request.  This is typically populated in
   the Request-URI of the SIP request.  Extracting the SIP-AOR AVP value

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   from the proper SIP header field is the Diameter client's
   responsibility.  Extensions to SIP (new SIP methods or new semantics)
   may require the SIP-AOR to be extracted from other parts of the
   request.

   If the SIP request includes some sort of authentication information,
   the Diameter client MUST include the user name, extracted from the
   authentication information of the SIP request, in the User-Name AVP
   value.

   The Message Format of the MAR command is as follows:

       <MAR> ::= < Diameter Header: 286, REQ, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { SIP-AOR }
                 { SIP-Method }
                 [ Destination-Host ]
                 [ User-Name ]
                 [ SIP-Server-URI ]
                 [ SIP-Number-Auth-Items ]
                 [ SIP-Auth-Data-Item ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.8.  Multimedia-Auth-Answer (MAA) Command

   The Multimedia-Auth-Answer (MAA) is indicated by the Command-Code set
   to 286 and the Command Flags' 'R' bit cleared.  The Diameter server
   sends this command in response to a previously received Diameter
   Multimedia-Auth-Request (MAR) command.

   In addition to the values already defined in RFC 3588 [RFC3588], the
   Result-Code AVP may contain one of the values defined in
   Section 10.1.

   If the Diameter server requires a User-Name AVP value to process the
   Diameter MAR request, but the Diameter MAR message did not contain a
   User-Name AVP value, the Diameter server MUST set the Result-Code AVP
   value to DIAMETER_USER_NAME_REQUIRED (see Section 10.1.2) and return
   it in a Diameter MAA message.  The Diameter server MAY include a
   SIP-Number-Auth-Items AVP and one or more SIP-Auth-Data-Item AVPs
   with authentication information (e.g., a challenge).  Upon reception

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   of this Diameter MAA message with the Result-Code AVP value set to
   DIAMETER_USER_NAME_REQUIRED, the SIP server typically requests
   authentication by generating a SIP 401 (Unauthorized) or SIP 407
   (Proxy Authentication Required) response back to the originator.

   If the User-Name AVP is present in the Diameter MAR message, the
   Diameter server MUST verify the existence of the user in the realm,
   i.e., the User-Name AVP value is a valid user within that realm.  If
   the Diameter server does not recognize the user name received in the
   User-Name AVP, the Diameter server MUST build a Diameter
   Multimedia-Auth-Answer (MAA) message and MUST set the Result-Code AVP
   to DIAMETER_ERROR_USER_UNKNOWN.

   If the SIP-Methods AVP value of the Diameter MAR message is set to
   REGISTER and a User-Name AVP is present, then the Diameter server
   MUST authorize that User-Name AVP value is able to use the URI
   included in the SIP-AOR AVP.  If this authorization fails, the
   Diameter server must set the Result-Code AVP to
   DIAMETER_ERROR_IDENTITIES_DONT_MATCH and send it in a Diameter
   Multimedia-Auth-Answer (MAA) message.

      Note: Correlation between User-Name and SIP-AOR AVP values is only
      required for SIP REGISTER request, to prevent a user from
      registering a SIP-AOR allocated to another user.  In other types
      of SIP requests (e.g., INVITE), the SIP-AOR indicates the intended
      destination of the request, rather than the originator of it.

   The Diameter server MUST verify whether the authentication scheme
   (SIP-Authentication-Scheme AVP value) indicated in the grouped
   SIP-Auth-Data-Item AVP is supported or not.  If that authentication
   scheme is not supported, then the Diameter server MUST set the
   Result-Code AVP to DIAMETER_ERROR_AUTH_SCHEME_NOT_SUPPORTED and send
   it in a Diameter Multimedia-Auth-Answer (MAA) message.

   If the SIP-Number-Auth-Items AVP is present in the Diameter MAR
   message, it indicates the number of authentication data items that
   the Diameter client is requesting.  It is RECOMMENDED that the
   Diameter server, when building the Diameter MAA message, includes a
   number of SIP-Auth-Data-Item AVPs that are a subset of the
   authentication data items requested by the Diameter client in the
   SIP-Number-Auth-Items AVP value of the Diameter MAR message.

   If the SIP-Server-URI AVP is present in the Diameter MAR message,
   then the Diameter server MUST compare the stored SIP server (assigned
   to the user) with the SIP-Server-URI AVP value (received in the
   Diameter MAR message).  If they don't match, the Diameter server MUST
   temporarily save the newly received SIP server assigned to the user,
   and MUST set an "authentication pending" flag for the user.  If they

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   match, the Diameter server shall clear the "authentication pending"
   flag for the user.

   In any other situation, if there is a success in processing the
   Diameter MAR command and the Diameter server stored the
   SIP-Server-URI, the Diameter server MUST set the Result-Code AVP
   value to DIAMETER_SUCCESS and return it in a Diameter MAA message.

   If there is a success in processing the Diameter MAR command, but the
   Diameter server does not store the SIP-Server-URI because the AVP was
   not present in the Diameter MAR command, then the Diameter server
   MUST set the Result-Code AVP value to either:

   1.  DIAMETER_SUCCESS_AUTH_SENT_SERVER_NOT_STORED, if the Diameter
       server is sending authentication credentials to create a
       challenge.

   2.  DIAMETER_SUCCESS_SERVER_NAME_NOT_STORED, if the Diameter server
       successfully authenticated the user and authorized the SIP server
       to proceed with the SIP request.

   Otherwise, the Diameter server MUST set the Result-Code AVP value to
   DIAMETER_UNABLE_TO_COMPLY, and it MUST NOT include any
   SIP-Auth-Data-Item AVP.

   The Message Format of the MAA command is as follows:

       <MAA> ::= < Diameter Header: 286, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Result-Code }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 [ User-Name ]
                 [ SIP-AOR ]
                 [ SIP-Number-Auth-Items ]
               * [ SIP-Auth-Data-Item ]
                 [ Authorization-Lifetime ]
                 [ Auth-Grace-Period ]
                 [ Redirect-Host ]
                 [ Redirect-Host-Usage ]
                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

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8.9.  Registration-Termination-Request (RTR) Command

   The Registration-Termination-Request (RTR) command is indicated by
   the Command-Code set to 287 and the Command Flags' 'R' bit set.  The
   Diameter server sends this command to the Diameter client in a SIP
   server to indicate to the SIP server that one or more SIP AORs have
   to be deregistered.  The command allows an operator to
   administratively cancel the registration of a user from a centralized
   Diameter server.

   The Diameter server has the capability to initiate the deregistration
   of a user and inform the SIP server by means of the Diameter RTR
   command.  The Diameter server can decide whether only one SIP AOR is
   going to be deregistered, a list of SIP AORs, or all the SIP AORs
   allocated to the user.

   The absence of a SIP-AOR AVP in the Diameter RTR message indicates
   that all the SIP AORs allocated to the user identified by the
   User-Name AVP are being deregistered.

   The Diameter server MUST include a SIP-Deregistration-Reason AVP
   value to indicate the reason for the deregistration.

   The Message Format of the RTR command is as follows:

       <RTR> ::= < Diameter Header: 287, REQ, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Host }
                 { SIP-Deregistration-Reason }
                 [ Destination-Realm ]
                 [ User-Name ]
               * [ SIP-AOR ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.10.  Registration-Termination-Answer (RTA) Command

   The Registration-Termination-Answer (RTA) is indicated by the
   Command-Code set to 287 and the Command Flags' 'R' bit cleared.  The
   Diameter client sends this command in response to a previously
   received Diameter Registration-Termination-Request (RTR) command.

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   In addition to the values already defined in RFC 3588 [RFC3588], the
   Result-Code AVP may contain one of the values defined in
   Section 10.1.

   If the SIP server (Diameter client) requires a User-Name AVP value to
   process the Diameter RTR request, but the Diameter RTR message did
   not contain a User-Name AVP value, the Diameter client MUST set the
   Result-Code AVP value to DIAMETER_USER_NAME_REQUIRED (see Section
   10.1.2) and return it in a Diameter RTA message.

   The SIP server (Diameter client) applies the administrative
   deregistration to each of the URIs included in each of the SIP-AOR
   AVP values, or, if there is no SIP-AOR AVP present in the Diameter
   RTR request, to all the URIs allocated to the User-Name AVP value.

   The value of the SIP-Deregistration-Reason AVP in the Diameter RTR
   command has an effect on the actions performed at the SIP server
   (Diameter client):

   o  If the value is set to PERMANENT_TERMINATION, then the user has
      terminated his/her registration to the realm.  If informing the
      interested parties (e.g., subscribers to the "reg" event
      [RFC3680]) about the administrative deregistration is supported
      through SIP procedures, the SIP server (Diameter client) will do
      so.  The Diameter Client in the SIP Server SHOULD NOT request a
      new user registration.  The SIP server clears the registration
      state of the deregistered AORs.

   o  If the value is set to NEW_SIP_SERVER_ASSIGNED, the Diameter
      server informs the SIP server (Diameter client) that a new SIP
      server has been allocated to the user, due to some reason.  The
      SIP server, if supported through SIP procedures, will inform the
      interested parties (e.g., subscribers to the "reg" event
      [RFC3680]) about the administrative deregistration at this SIP
      server.  The Diameter client in the SIP server SHOULD NOT request
      a new user registration.  The SIP server clears the registration
      state of the deregistered SIP AORs.

   o  If the value is set to SIP_SERVER_CHANGE, the Diameter server
      informs the SIP server (Diameter client) that a new SIP server has
      to be allocated to the user, e.g., due to user's capabilities
      requiring a new SIP server, or not enough resources in the current
      SIP server.  If informing the interested parties about the
      administrative deregistration is supported through SIP procedures
      (e.g., subscriptions to the "reg" event [RFC3680]), the SIP server
      will do so.  The Diameter client in the SIP Server SHOULD NOT
      request a new user registration.  The SIP server clears the
      registration state of the deregistered SIP AORs.

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   o  If the value is set to REMOVE_SIP_SERVER, the Diameter server
      informs the SIP server (Diameter client) that the SIP server will
      no longer be bound in the Diameter server with that user.  The SIP
      server can delete all data related to the user.

   The Message Format of the RTA command is as follows:

       <RTA> ::= < Diameter Header: 287, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Result-Code }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 [ Authorization-Lifetime ]
                 [ Auth-Grace-Period ]
                 [ Redirect-Host ]
                 [ Redirect-Host-Usage ]
                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.11.  Push-Profile-Request (PPR) Command

   The Push-Profile-Request (PPR) command is indicated by the
   Command-Code set to 288 and the Command Flags' 'R' bit set.  The
   Diameter server sends this command to the Diameter client in a SIP
   server to update either the user profile of an already registered
   user in that SIP server or the SIP accounting information.  This
   allows an operator to modify the data of a user profile or the
   accounting information and push it to the SIP server where the user
   is registered.

   Each user has a user profile associated with him/her and other
   accounting information.  The profile or the accounting information
   may change with time, e.g., due to addition of new services to the
   user.  When the user profile or the accounting information changes,
   the Diameter server sends a Diameter Push-Profile-Request (PPR)
   command to the Diameter client in a SIP server, in order to start
   applying those new services.

   A PPR command MAY contain a SIP-Accounting-Information AVP that
   updates the addresses of the accounting servers.  Changes in the
   addresses of the accounting servers take effect immediately.  The
   Diameter client SHOULD close any existing accounting session with the
   existing server and start providing accounting information to the
   newly acquired accounting server.

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   A PPR command MAY contain zero or more SIP-User-Data AVP values
   containing the new user profile.  On selecting the type of user data,
   the Diameter server SHOULD take into account the supported formats at
   the SIP server (SIP-Supported-User-Data-Type AVP sent in a previous
   SAR message) and the local policy.

   The User-Name AVP indicates the user to whom the profile is
   applicable.

   The Message Format of the PPR command is as follows:

       <PPR> ::= < Diameter Header: 288, REQ, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { User-Name }
               * [ SIP-User-Data ]
                 [ SIP-Accounting-Information ]
                 [ Destination-Host ]
                 [ Authorization-Lifetime ]
                 [ Auth-Grace-Period ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]

8.12.  Push-Profile-Answer (PPA) Command

   The Push-Profile-Answer (PPA) is indicated by the Command-Code set to
   288 and the Command Flags' 'R' bit cleared.  The Diameter client
   sends this command in response to a previously received Diameter
   Push-Profile-Request (PPR) command.

   In addition to the values already defined in RFC 3588 [RFC3588], the
   Result-Code AVP may contain one of the values defined in
   Section 10.1.

   If there is no error when processing the received Diameter PPR
   message, the SIP server (Diameter client) MUST download the received
   user profile from the SIP-User-Data AVP values in the Diameter PPR
   message and store it associated with the user specified in the
   User-Name AVP value.

   If the SIP server does not recognize or does not support some of the
   data transferred in the SIP-User-Data AVP values, the Diameter client
   in the SIP server MUST return a Diameter PPA message that includes a

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   Result-Code AVP set to the value
   DIAMETER_ERROR_NOT_SUPPORTED_USER_DATA.

   If the SIP server (Diameter client) receives a Diameter PPR message
   with a User-Name AVP that is unknown, the Diameter client MUST set
   the Result-Code AVP value to DIAMETER_ERROR_USER_UNKNOWN and MUST
   return it to the Diameter server in a Diameter PPA message.

   If the SIP server (Diameter client) receives in the
   SIP-User-Data-Content AVP value (of the grouped SIP-User-Data AVP)
   more data than it can accept, it MUST set the Result-Code AVP value
   to DIAMETER_ERROR_TOO_MUCH_DATA and MUST return it to the Diameter
   server in a Diameter PPA message.  The SIP server MUST NOT override
   the existing user profile with the one received in the PPR message.

   If the Diameter server receives the Result-Code AVP value set to
   DIAMETER_ERROR_TOO_MUCH_DATA in a Diameter PPA message, it SHOULD
   force a new re-registration of the user by sending to the Diameter
   client a Diameter Registration-Termination-Request (RTR) with the
   SIP-Deregistration-Reason AVP value set to SIP_SERVER_CHANGE.  This
   will force a re-registration of the user and will trigger a selection
   of a new SIP server.

   If the Diameter client is not able to honor the command, for any
   other reason, it MUST set the Result-Code AVP value to
   DIAMETER_UNABLE_TO_COMPLY and it MUST return it in a Diameter PPA
   message.

   The Message Format of the PPA command is as follows:

       <PPA> ::= < Diameter Header: 288, PXY >
                 < Session-Id >
                 { Auth-Application-Id }
                 { Result-Code }
                 { Auth-Session-State }
                 { Origin-Host }
                 { Origin-Realm }
                 [ Redirect-Host ]
                 [ Redirect-Host-Usage ]
                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]


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