SSCA SDP Protocol 4

Question 1

What is the purpose of the 'a=ice-ufrag' and 'a=ice-pwd' attributes in SDP?

Accepted Answer

They carry ICE credentials for NAT traversal

Answer

The a=ice-ufrag and a=ice-pwd attributes provide the username fragment and password used to authenticate ICE connectivity checks.

Question 2

In SDP offer/answer, what must an answerer do with a media stream it does not support?

Accepted Answer

Set the port to 0 in the m= line of the answer

Answer

Per RFC 3264, if the answerer cannot support a media stream, it must include the m= line with port set to 0 to reject it.

Question 3

Which SDP attribute carries fingerprint information used for DTLS-SRTP key negotiation?

Accepted Answer

a=fingerprint

Answer

The a=fingerprint attribute contains a hash of the certificate used in the DTLS handshake, enabling peers to verify each other's identity for DTLS-SRTP.

Question 4

What does 'a=setup:actpass' mean in SDP?

Accepted Answer

The endpoint can act as either DTLS client or server

Answer

The 'actpass' setup attribute indicates the endpoint is willing to act as either the DTLS active (client) or passive (server) role, letting the other side choose.

Question 5

What is the function of the 'a=candidate' attribute in SDP?

Accepted Answer

It lists ICE candidates (IP addresses and ports) for media connectivity

Answer

The a=candidate attribute carries ICE candidate information including transport address, priority, and type (host, srflx, relay) used in NAT traversal.

(SSCA) Sip School Certified Associate Practice Test

(SSCA) Sip School Certified Associate Practice Test

SSCA SDP Protocol 4