SSCA SIP Protocols & Call Flow Fundamentals 5

Question 1

In SIP, which message flow completes the three-way handshake for an INVITE transaction?

Accepted Answer

INVITE → 200 OK → ACK

Answer

The SIP INVITE transaction uses a three-way handshake: INVITE from caller, 200 OK from callee, and ACK from caller.

Question 2

What SIP header is used by a UAC to indicate the address where it wants to receive future in-dialog requests?

Accepted Answer

Contact

Answer

The Contact header provides a direct SIP URI for future requests within the dialog, bypassing the registrar.

Question 3

Which SIP response class indicates server-side errors?

Accepted Answer

5xx

Answer

5xx responses indicate that the server failed to fulfill an apparently valid request due to a server-side error.

Question 4

In SIP presence, which method does a watcher use to receive real-time state updates from a presentity?

Accepted Answer

SUBSCRIBE/NOTIFY

Answer

A watcher sends SUBSCRIBE to the presence agent, which then sends NOTIFY messages whenever the presentity's state changes.

Question 5

What does the SIP 'timer B' control in the INVITE transaction?

Accepted Answer

The time a client waits for a final response before considering the transaction failed

Answer

Timer B is the INVITE transaction timeout — if no final response arrives before Timer B fires, the client considers the transaction failed.

(SSCA) Sip School Certified Associate Practice Test