SIP Session Management 2

Question 1

Which SIP method is used to modify an existing session's parameters, such as changing the codec mid-call?

Accepted Answer

RE-INVITE

Answer

A re-INVITE is sent within an established dialog to renegotiate session parameters like media codecs or IP addresses.

Question 2

What is the purpose of the SIP UPDATE method compared to re-INVITE?

Accepted Answer

UPDATE modifies session state before the answer is received, avoiding hold

Answer

RFC 3311 UPDATE allows session parameter changes before the final response is sent, avoiding the need to place the call on hold.

Question 3

In a SIP dialog, what does the Route header set contain?

Accepted Answer

The list of proxy servers to traverse for in-dialog requests

Answer

The Route header set is built from Record-Route headers and ensures subsequent in-dialog requests traverse the same proxy path.

Question 4

What SIP response code indicates the session was successfully established?

Accepted Answer

200 OK

Answer

A 200 OK response to an INVITE confirms the session has been accepted and established by the callee.

Question 5

Which SIP timer governs how long a UAC waits for a final response before retransmitting an INVITE?

Accepted Answer

Timer B

Answer

Timer B is the INVITE transaction timeout timer; if no final response is received within 64*T1, the transaction times out.

(SIP) Session Initiation Protocol Practice Test