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.

   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

      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.

   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 ]

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

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