SSCA Session Management 3 — Questions and Answers
Question 1: What does the 'Min-SE' header in SIP Session Timers indicate?
- The minimum session expiry the UA will accept (Correct answer)
- The minimum number of session refresh attempts allowed
- The minimum codec bitrate for the session
- The minimum hop count for session requests
Correct answer: The minimum session expiry the UA will accept
The Min-SE header advertises the minimum value a UA will accept for the Session-Expires interval, preventing excessively short refresh periods.
Question 2: In a SIP call transfer using REFER, what does the Refer-To header contain?
- The SIP URI of the transfer target (Correct answer)
- The reason for the transfer
- The identity of the transferring party
- The codec list for the new session
Correct answer: The SIP URI of the transfer target
The Refer-To header in a REFER request contains the SIP URI identifying the target to which the recipient should direct a new request.
Question 3: Which SIP response code indicates that the session description offered in an INVITE is not acceptable?
- 415 Unsupported Media Type
- 488 Not Acceptable Here (Correct answer)
- 406 Not Acceptable
- 606 Not Acceptable
Correct answer: 488 Not Acceptable Here
488 Not Acceptable Here indicates that the session description (SDP) in the request is not acceptable at this time, often due to codec mismatch.
Question 4: What is the purpose of the PRACK method in SIP?
- To provision reliable transmission of provisional responses (1xx) (Correct answer)
- To permanently acknowledge a final response
- To pre-authorize a session before it is established
- To partially cancel a pending INVITE
Correct answer: To provision reliable transmission of provisional responses (1xx)
PRACK (Provisional ACKnowledgement) provides reliable delivery of provisional responses when the 100rel option tag is used, as defined in RFC 3262.
Question 5: During early dialog SIP negotiation, which header signals that a UAC requires reliable provisional responses?
- Supported: 100rel
- Require: 100rel (Correct answer)
- Allow: PRACK
- RSeq: 1
Correct answer: Require: 100rel
Including 'Require: 100rel' in an INVITE mandates that the UAS send provisional responses reliably using the PRACK mechanism defined in RFC 3262.
Question 6: Which SIP mechanism allows a UA to be notified when a subscribed resource changes state during a session?
- PUBLISH/SUBSCRIBE
- SUBSCRIBE/NOTIFY (Correct answer)
- REGISTER/OPTIONS
- REFER/NOTIFY
Correct answer: SUBSCRIBE/NOTIFY
The SUBSCRIBE/NOTIFY mechanism (RFC 6665) allows a UA to subscribe to event packages and receive NOTIFY messages when the subscribed resource state changes.
Question 7: What is 'session forking' in SIP?
- Splitting audio and video into separate streams
- A proxy forwarding an INVITE to multiple potential endpoints simultaneously (Correct answer)
- Dividing a session timer into multiple refresh intervals
- Routing a session through multiple proxies sequentially
Correct answer: A proxy forwarding an INVITE to multiple potential endpoints simultaneously
Session forking occurs when a SIP proxy forwards an INVITE to multiple destinations in parallel, allowing the caller to connect to whichever endpoint answers first.
SSCA Session Management 3
What does the 'Min-SE' header in SIP Session Timers indicate?