SSCA VoIP Technologies & Network Integration 5

Question 1

What is the purpose of the Record-Route header in SIP?

Accepted Answer

To force subsequent in-dialog requests to traverse specific proxies

Answer

Proxies insert themselves into the Record-Route header so that future requests within the dialog continue to pass through them.

Question 2

Which mechanism in ICE (Interactive Connectivity Establishment) is used when direct peer-to-peer media is not possible through NAT?

Accepted Answer

TURN relay candidates

Answer

TURN (Traversal Using Relays around NAT) provides relay candidates that route media through a server when direct connectivity is impossible.

Question 3

In VoIP network design, what is the recommended maximum packet loss rate for acceptable voice quality?

Accepted Answer

Less than 1%

Answer

Packet loss above 1% begins to noticeably degrade voice quality; most QoS designs target sub-1% loss for voice traffic.

Question 4

What does the SIP REFER method allow a UA to do?

Accepted Answer

Transfer a call or direct another UA to contact a third party

Answer

REFER instructs the recipient to initiate a new contact with a URI provided in the Refer-To header, enabling call transfer scenarios.

Question 5

Which SIP feature allows a provisional response (1xx) to be acknowledged to avoid retransmissions over unreliable transports?

Accepted Answer

Reliable Provisional Responses (PRACK) per RFC 3262

Answer

RFC 3262 defines PRACK (Provisional Acknowledgment) to reliably deliver provisional responses when using unreliable transports like UDP.

(SSCA) Sip School Certified Associate Practice Test