Which two header fields does a SIP Agent Server use to indicate that the message needs Provisional Response Acknowledgment? (Choose two.)
Click on the arrows to vote for the correct answerA. B. C. D. E. F.
When a Session Initiation Protocol (SIP) User Agent Server (UAS) sends a Provisional Response (1xx) to a SIP User Agent Client (UAC), it can request an acknowledgment from the UAC indicating that the Provisional Response was received correctly. This acknowledgment is called a Provisional Response Acknowledgment (PRACK).
To request a PRACK, a SIP UAS can use two header fields:
Require: 100rel The Require header field is used by a SIP UAS to require certain functionality from the UAC for a successful communication. In this case, the UAS includes the 100rel option tag in the Require header field to indicate that it requires support for PRACK from the UAC.
RSeq: [Numeric value that uniquely identifies the response message] The RSeq header field is used by a SIP UAS to provide a sequence number for each Provisional Response that it sends. The UAS includes the RSeq header field in the Provisional Response to indicate that the response requires a PRACK from the UAC with the same RSeq value.
Therefore, options B and E are the correct answers as they refer to the Require header and the RSeq header, respectively.