SIP Session Management 3

Question 1

What happens if a SIP UAS receives a re-INVITE with an SDP offer it cannot support?

Accepted Answer

It responds with 488 Not Acceptable Here

Answer

It responds with 404 Not Found

Answer

It responds with 300 Multiple Choices

Answer

It sends a BYE to terminate the session

Question 2

Which SIP mechanism allows a UA to detect if a session is still active when no media is flowing?

Accepted Answer

Session timers (RFC 4028)

Answer

Registration refresh

Answer

PRACK retransmission

Answer

180 Ringing keepalive

Question 3

In SIP session timers, what does the 'refresher' parameter in the Session-Expires header indicate?

Accepted Answer

Which UA is responsible for sending the refresh request

Answer

The maximum session duration in seconds

Answer

The codec to use during refresh

Answer

The proxy that handles the refresh

Question 4

What SIP response is sent by a UAS when it receives a BYE request that references a dialog it cannot find?

Accepted Answer

481 Call/Transaction Does Not Exist

Answer

404 Not Found

Answer

486 Busy Here

Answer

403 Forbidden

Question 5

During a SIP call transfer using REFER, which header carries the transfer target's URI?

Accepted Answer

Refer-To

Answer

Contact

Answer

P-Asserted-Identity

Answer

Referred-By

Question 6

What is the role of NOTIFY in a REFER-based call transfer?

Accepted Answer

Report the status of the REFER subscription (e.g., 100 Trying, 200 OK)

Answer

Tear down the original session

Answer

Negotiate new codecs for the transferred call

Answer

Authenticate the transfer target

Question 7

Which condition causes SIP early dialogs to be created?

Accepted Answer

Receipt of a provisional response (1xx) with a To tag

Answer

Receipt of a 200 OK with a From tag

Answer

Sending a REGISTER request

Answer

Receipt of a 4xx response