SSCA SIP Headers 2 — Questions and Answers
Question 1: Which SIP header is used to indicate the maximum number of times a request can be forwarded by proxies?
- Max-Forwards (Correct answer)
- Via
- Route
- Contact
Correct answer: Max-Forwards
The Max-Forwards header limits the number of hops a SIP request can traverse, preventing infinite loops.
Question 2: What is the purpose of the Record-Route header in SIP?
- To record the path taken by a request so proxies remain in the signaling path (Correct answer)
- To log call detail records for billing
- To specify the destination URI of the request
- To indicate the caller's identity
Correct answer: To record the path taken by a request so proxies remain in the signaling path
Record-Route is inserted by proxies to ensure they remain in the signaling path for subsequent requests within a dialog.
Question 3: Which header field carries the SIP address of the party sending the request?
- To
- From (Correct answer)
- Contact
- P-Asserted-Identity
Correct answer: From
The From header identifies the logical originator of the request and includes a tag parameter after the dialog is established.
Question 4: What does the Expires header specify in a REGISTER request?
- The time until the registration binding expires (Correct answer)
- The time the server has to respond
- The duration of an active call
- The codec negotiation timeout
Correct answer: The time until the registration binding expires
The Expires header in a REGISTER request indicates how long the binding between the AOR and Contact URI should remain valid.
Question 5: Which SIP header is used by a UAC to list the supported SIP extensions?
- Allow
- Require
- Supported (Correct answer)
- Proxy-Require
Correct answer: Supported
The Supported header (formerly called Allow-Events in some contexts) lists option tags for extensions the UAC supports but does not require.
Question 6: In a SIP response, which header indicates the methods accepted by the UAS?
- Supported
- Allow (Correct answer)
- Require
- Accept
Correct answer: Allow
The Allow header lists the SIP methods supported by the UA sending the message, commonly included in responses.
Question 7: What is the function of the Content-Length header in SIP?
- Specifies the number of bytes in the message body (Correct answer)
- Indicates the number of SIP headers present
- Limits the size of future requests
- Defines the codec payload size
Correct answer: Specifies the number of bytes in the message body
Content-Length indicates the byte count of the message body, allowing the receiver to correctly parse the body.
SSCA SIP Headers 2
Which SIP header is used to indicate the maximum number of times a request can be forwarded by proxies?