SSCA SIP Headers 5 — Questions and Answers
Question 1: Which SIP header is used to convey the reason for a call termination or rejection?
- Warning
- Reason (Correct answer)
- Retry-After
- Termination-Info
Correct answer: Reason
The Reason header provides additional information about why a call was terminated or rejected, using protocol and cause code values.
Question 2: What does the Accept-Language header indicate in a SIP request?
- The preferred languages for reason phrases and session descriptions in the response (Correct answer)
- The language of the SDP body
- The caller's geographic region
- The encoding format for binary headers
Correct answer: The preferred languages for reason phrases and session descriptions in the response
Accept-Language indicates the preferred natural languages for human-readable content in responses, similar to its HTTP counterpart.
Question 3: In SIP event notification, which header specifies the event package being subscribed to?
- Allow-Events
- Event (Correct answer)
- Subscription-State
- Notify-Info
Correct answer: Event
The Event header in SUBSCRIBE and NOTIFY requests specifies which event package the subscription or notification applies to.
Question 4: What does a Subscription-State header value of 'terminated' indicate in a NOTIFY?
- The subscription has ended and no further NOTIFYs will be sent (Correct answer)
- The subscriber has been temporarily blocked
- The server is restarting the subscription
- The event state is unknown
Correct answer: The subscription has ended and no further NOTIFYs will be sent
A Subscription-State of 'terminated' tells the subscriber that the subscription is over and no additional NOTIFY requests will follow.
Question 5: Which SIP header is used to group multiple related calls together, such as in a conference?
- Join (Correct answer)
- Call-Info
- Call-ID
- Join-Info
Correct answer: Join
The Join header is used in an INVITE to mix the new call into an existing dialog, commonly used for three-way calling or conference bridging.
Question 6: What is the purpose of the Retry-After header in a SIP 503 response?
- Tells the client how many seconds to wait before retrying the request (Correct answer)
- Specifies the maximum number of retry attempts allowed
- Indicates the fallback server address
- Sets the timer for re-registration
Correct answer: Tells the client how many seconds to wait before retrying the request
The Retry-After header in a 503 Service Unavailable response advises the client to wait the specified number of seconds before sending another request.
Question 7: Which header would contain 'sip:bob@biloxi.com;transport=tcp' to indicate a specific transport for routing?
- Via
- Route
- Contact (Correct answer)
- Request-URI
Correct answer: Contact
The Contact header can include URI parameters such as 'transport=tcp' to indicate that the UA prefers or requires TCP for incoming requests.
SSCA SIP Headers 5
Which SIP header is used to convey the reason for a call termination or rejection?