SSCA SIP Headers 3 — Questions and Answers
Question 1: Which SIP header is used to route a request through a specific set of proxies in order?
- Record-Route
- Route (Correct answer)
- Via
- Path
Correct answer: Route
The Route header specifies a pre-determined list of SIP proxies through which the request must pass.
Question 2: What does a SIP Warning header provide?
- Additional information about why a response was generated, beyond the status code (Correct answer)
- Authentication challenges for the client
- Routing instructions for the next hop
- Encryption key material
Correct answer: Additional information about why a response was generated, beyond the status code
The Warning header carries human-readable information about issues encountered when processing a request, such as incompatible session descriptions.
Question 3: Which header would a SIP proxy add to indicate the address at which it can be reached for future requests?
- Contact
- Via
- Record-Route (Correct answer)
- Path
Correct answer: Record-Route
A proxy inserts a Record-Route header with its own URI so it remains in the signaling path for subsequent in-dialog requests.
Question 4: What is the purpose of the Replaces header in SIP?
- To replace an existing dialog with a new INVITE (Correct answer)
- To substitute one codec for another mid-call
- To re-register a contact address
- To transfer billing from one account to another
Correct answer: To replace an existing dialog with a new INVITE
The Replaces header allows a new INVITE to atomically replace an existing confirmed or early dialog, used in call transfer scenarios.
Question 5: What information does the P-Asserted-Identity header carry?
- The verified identity of the user sending the request, as asserted by a trusted network element (Correct answer)
- The public IP of the originating UA
- The SIP domain of the registrar
- The preferred codec of the caller
Correct answer: The verified identity of the user sending the request, as asserted by a trusted network element
P-Asserted-Identity carries the authenticated identity of the originating user, inserted by a trusted SIP proxy after verifying credentials.
Question 6: Which SIP header specifies the body content type, such as 'application/sdp'?
- Content-Encoding
- Content-Type (Correct answer)
- Accept
- MIME-Version
Correct answer: Content-Type
The Content-Type header describes the media type of the SIP message body, with 'application/sdp' being the most common value.
Question 7: In which scenario would a SIP UA include the Require header?
- When it needs the remote party to support a specific extension to process the request (Correct answer)
- When listing optional extensions it supports
- When specifying codecs for the session
- When indicating supported transport protocols
Correct answer: When it needs the remote party to support a specific extension to process the request
The Require header lists option tags for extensions that must be understood by the recipient; if not supported, the recipient returns 420 Bad Extension.
SSCA SIP Headers 3
Which SIP header is used to route a request through a specific set of proxies in order?