3.3.5.1 Receiving a Bandwidth Admission Control Check Request Message

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If the Allocate Request message contains a Bandwidth Admission Control Message attribute with a value of Reservation Check, the request is processed as follows:

  • The request MUST include a Bandwidth Reservation Amount attribute, as specified in section 2.2.3. If this attribute is not included, the server MUST continue to process the Allocate Request message as specified in [MS-TURN] section 3.3.5.1 and ignore the Bandwidth Admission Control Message action.

  • The request MUST include a Remote Site Address attribute, as specified in section 2.2.4. If this attribute is not included, the server MUST continue to process the Allocate Request message as specified in [MS-TURN] section 3.3.5.1 and ignore the Bandwidth Admission Control Message action.

  • If the peer is using a TURN server and has an allocated transport address, the request MUST include a Remote Relay Site Address attribute, as specified in section 2.2.5, containing the transport address allocated by the TURN server.

  • The request SHOULD include a Local Site Address attribute, as specified in section 2.2.6. If this attribute is not present, the server (2) MUST use the source transport address of the message to identify the requesting client’s local site address.

  • If the server allocated a public transport address on behalf of the client as part of processing the Allocate Request message, the server MUST use the allocated transport address to identify the requesting client’s Local Relay Site Address.

  • The request SHOULD include a MS-Service Quality attribute, as specified in [MS-TURN] section 2.2.2.22. If this attribute is not present, the server SHOULD treat the Reservation Check as a check for an audio stream.

  • The request SHOULD include the SIP Call Identifier attribute, as specified in section 2.2.13.

  • The request MUST include the Location Profile attribute, as specified in section 2.2.14.

If all of the required attributes are present and valid, the server (2) MUST use the bandwidth admission control network topology to map the site address attributes present in the request to network sites, and then map the network sites to the network paths connecting the sites. The server (2) MUST check the bandwidth request against the bandwidth policy for the network paths. There are three possible network paths that can be checked:

  • The network path between the network sites mapped by the Remote Site Address and the Remote Relay Site Address.

  • The network path between the network sites mapped by the Local Site Address and the Local Relay Site Address.

  • The network path between the network sites mapped by the Local Site Address and the Remote Site Address.

Once the server has finished checking the bandwidth policy for the available network paths, it MUST respond with an Allocate Response message:

  • The response MUST be formed as specified in [MS-TURN] section 3.3.5.1.

  • The response MUST include a Bandwidth Admission Control Message attribute with a value of Reservation Check, as specified in section 2.2.1.

  • The response MUST include a Remote Site Address Response attribute, as specified in section 2.2.8. If the bandwidth policy passed for the network path between the network sites identified by the Remote Site Address and the Local Site Address, the attribute MUST have the Valid bit set (V="1") and the bandwidth values set to the amount of bandwidth the policy allowed. If the bandwidth policy failed, the attribute MUST have the Valid bit cleared (V="0") and the bandwidth values set to zero. If the bandwidth policy supports redirecting the connection to PSTN, the server MUST set the PSTN Failover bit (F="1"), otherwise the PSTN Failover bit MUST be cleared (F="0").

  • If a Remote Relay Site Address attribute was present in the request, the response MUST include a Remote Relay Site Address Response attribute, as specified in section 2.2.9. If the bandwidth policy passed for the network path between the network sites identified by the Remote Site Address and the Remote Relay Site Address, the attribute MUST have the Valid bit set (V="1") and the bandwidth values set to the amount of bandwidth the policy allowed. If the bandwidth policy failed, the attribute MUST have the Valid bit cleared (V="0") and the bandwidth values set to zero.

  • If the server allocated a public transport address on behalf of the client, the response MUST include a Local Relay Site Address Response attribute, as specified in section 2.2.11. If the bandwidth policy passed for the network path between the network sites identified by the Local Site Address and the Local Site Relay Address, the attribute MUST have the Valid bit set (V="1") and the bandwidth values set to the amount of bandwidth the policy allowed. If the bandwidth policy failed, the attribute MUST have the Valid bit cleared (V="0") and the bandwidth values set to zero.

  • The response MUST include a Local Site Address Response attribute, as specified in section 2.2.10. If the bandwidth policy passed for the network path between the network sites identified by the Remote Site Address and the Local Site Address, the attribute MUST have the Valid bit set (V="1") and the bandwidth values set to the amount of bandwidth the policy allowed. If the bandwidth policy failed, the attribute MUST have the Valid bit cleared (V="0") and the bandwidth values set to zero. If the bandwidth policy supports redirecting the connection to PSTN, the server MUST set the PSTN Failover bit (F="1"); otherwise the PSTN Failover bit MUST be cleared (F="0").