Which description of the expected behavior of a SIP User Agent Client that received a reliable provisional that contains an offer is true?
Click on the arrows to vote for the correct answer
A. B. C. D. E.A.
When a Session Initiation Protocol (SIP) User Agent Client (UAC) receives a reliable provisional response that contains an offer, it means that the response is acknowledged by the network, and the UAC can rely on it. In this scenario, the UAC has a few options on how to proceed.
Option A: The UAC must include an answer in a PRACK This option is incorrect because the UAC is not required to include an answer in a PRACK. The purpose of a PRACK (Provisional Response Acknowledgement) message is to acknowledge the reliable provisional response and inform the UAS (User Agent Server) that the response has been received. The UAC may choose to include an answer in the PRACK, but it is not mandatory.
Option B: The UAC must include an answer in a PRACKACK This option is incorrect because there is no such thing as a PRACKACK message in SIP. The correct term is PRACK, and the purpose of the PRACK is to acknowledge the reliable provisional response and provide a way for the UAC to send an answer to the UAS.
Option C: The UAC may include an answer in an ACK This option is correct because the UAC may choose to include an answer in the ACK (Acknowledgement) message that acknowledges the final response from the UAS. The ACK is not used to carry any media or signaling information, but the UAC can use the ACK to send its answer to the UAS.
Option D: The UAC may include an answer in a PRACK This option is correct because the UAC may choose to include an answer in the PRACK message. The PRACK message is used to acknowledge the reliable provisional response and provide a way for the UAC to send its answer to the UAS.
Option E: The UAC may include an answer in a PRACKACK This option is incorrect because there is no such thing as a PRACKACK message in SIP.
In summary, the correct answers are C and D. The UAC may include an answer in either the ACK or PRACK messages when it receives a reliable provisional response that contains an offer. However, it is important to note that including the answer in the PRACK message is not mandatory, and the UAC can choose to include the answer in the ACK message instead.