UAS-Side PRACK Interworking

The Oracle® Enterprise Session Border Controller applies PRACK interworking on the UAS side when:

• A SIP INVITE contains the 100rel tag in a Require or Supported header
• The egress SIP interface is enabled with the 100rel-interworking option
• The UAS does send reliable provisional responses

When the UAC does not support RFC 3262, the Oracle® Enterprise Session Border Controller generates a PRACK request to acknowledge the response. It also converts the response to non-reliable by removing the 100 rel tag from the Require header and removing the RSeq header from the response.

In the case of the UAS, the Oracle® Enterprise Session Border Controller matches the PRACK to a converted reliable provisional response using the PRACK’s RAck header. If it finds a matching response, the Oracle® Enterprise Session Border Controller generates a 200 OK to the PRACK. And if it finds no match, then it generates a 481 Call Leg/Transaction Does Not Exist response. The Oracle® Enterprise Session Border Controller generates a 400 Bad Request response if either the RAck is not in the PRACK request or it is not formatted properly.

The call flow for this application looks like this: