SSCA SIP Protocols & Call Flow Fundamentals 3

Question 1

What is the function of the Record-Route header in SIP?

Accepted Answer

To keep a proxy in the signaling path for subsequent requests

Answer

Record-Route is inserted by proxies that want to remain in the signaling path for all subsequent in-dialog requests.

Question 2

In SIP digest authentication, what is the purpose of the 'nonce' value?

Accepted Answer

To prevent replay attacks by providing a unique challenge each time

Answer

The nonce is a server-generated unique value included in the WWW-Authenticate challenge to prevent replay attacks.

Question 3

Which SIP header field is used to specify the maximum number of times a request can be forwarded by proxies?

Accepted Answer

Max-Forwards

Answer

Max-Forwards limits the number of proxy hops; each proxy decrements it by one and rejects the request if it reaches zero.

Question 4

In SIP call flow, which message confirms that ringing has been answered and the session is established?

Accepted Answer

200 OK to INVITE

Answer

200 OK to INVITE signals that the called party has accepted the call, establishing the dialog.

Question 5

What does the SIP REFER method primarily accomplish?

Accepted Answer

Instructs the recipient to contact a third party, enabling call transfer

Answer

REFER is used to implement call transfer by telling the recipient to send a request (usually INVITE) to the URI in the Refer-To header.

(SSCA) Sip School Certified Associate Practice Test