SSCA SIP Protocols & Call Flow Fundamentals 2 — Questions and Answers
Question 1: Which SIP response code indicates that the request has been received and is being processed, but no final response has been sent?
- 100 Trying (Correct answer)
- 180 Ringing
- 183 Session Progress
- 200 OK
Correct answer: 100 Trying
100 Trying is a provisional response indicating the request was received and is being forwarded to the next hop.
Question 2: In SIP, what is the purpose of the 'branch' parameter in the Via header?
- To identify the transaction uniquely (Correct answer)
- To specify the transport protocol
- To indicate the hop count
- To record the route taken
Correct answer: To identify the transaction uniquely
The 'branch' parameter is a transaction ID that uniquely identifies each transaction, and must start with 'z9hG4bK' in RFC 3261.
Question 3: What SIP method is used to query the capabilities of a SIP endpoint without establishing a session?
- OPTIONS (Correct answer)
- INFO
- NOTIFY
- SUBSCRIBE
Correct answer: OPTIONS
The OPTIONS method allows a client to query a server about its supported methods, extensions, and codecs.
Question 4: Which header in a SIP INVITE carries the session description (media parameters)?
- Content-Type: application/sdp in the body (Correct answer)
- Media header
- Session header
- Codec header
Correct answer: Content-Type: application/sdp in the body
SIP carries session description via an SDP body, with the Content-Type header set to application/sdp.
Question 5: A SIP BYE request terminates which type of dialog?
- An established INVITE dialog (Correct answer)
- A SUBSCRIBE dialog
- A REGISTER transaction
- An OPTIONS transaction
Correct answer: An established INVITE dialog
BYE is sent within an established INVITE dialog to terminate an active session.
Question 6: In a SIP re-INVITE, what is the primary purpose?
- To modify session parameters of an existing call (Correct answer)
- To transfer a call to another party
- To put a call on hold only
- To register a new contact address
Correct answer: To modify session parameters of an existing call
A re-INVITE is sent within an existing dialog to modify session parameters such as codec, media direction, or IP address.
Question 7: Which SIP response code means 'Moved Temporarily' and provides a new address to try?
- 302 (Correct answer)
- 301
- 305
- 380
Correct answer: 302
302 Moved Temporarily instructs the client to retry the request at the URI specified in the Contact header.
SSCA SIP Protocols & Call Flow Fundamentals 2
Which SIP response code indicates that the request has been received and is being processed, but no final response has been sent?