SIP Interoperability and Integration 5

Question 1

A SIP endpoint receives a 421 Extension Required response. What does this indicate?

Accepted Answer

The server requires a specific SIP extension listed in the Require header of the response

Answer

421 Extension Required means the server requires the client to include a specific SIP extension (listed in the Require header) to proceed.

Question 2

Which SIP feature allows a UA to detect that a remote peer has gone silent (e.g., due to a network failure) without waiting for a BYE?

Accepted Answer

SIP OPTIONS keep-alive

Answer

SIP OPTIONS messages sent at regular intervals act as keep-alives to detect if the remote UA or proxy is still reachable.

Question 3

When integrating SIP with a legacy PBX using a SIP trunk, which parameter mismatch most commonly causes one-way audio?

Accepted Answer

NAT traversal failure causing incorrect RTP IP/port in SDP

Answer

One-way audio typically occurs when the SDP contains a private IP that is unreachable from the remote side due to NAT, causing RTP to flow only in one direction.

Question 4

In SIP, the P-Asserted-Identity (PAI) header is typically used to:

Accepted Answer

Carry the verified caller identity within a trusted network domain

Answer

PAI (RFC 3325) carries the verified identity of the caller as asserted by a trusted SIP proxy or SBC within a closed trusted network.

Question 5

Which SIP header is used to convey the original DNIS (Dialed Number Identification Service) information when a call is forwarded or transferred?

Accepted Answer

History-Info

Answer

History-Info (RFC 7044) records the sequence of Request-URIs a request has been retargeted through, preserving the original DNIS and forwarding history.

(SIP) Session Initiation Protocol Practice Test

(SIP) Session Initiation Protocol Practice Test

SIP Interoperability and Integration 5