350-801 Question #442: Real Exam Question with Answer & Explanation

The correct answer is D: G.711ulaw, G.711alaw, G.722, and G.729. In an SDP 'm=' line, the codecs are listed as payload types (PT) in order of preference, and these payload types map to specific codecs defined in the 'a=rtpmap' lines. Assuming a common SDP snippet, the codecs are ordered as G.711ulaw, G.711alaw, G.722, and G.729.

Media and QoS

Question

Refer to the exhibit. An engineer must provide a list of codecs based on the media attribute of an SDP body snippet. Which codecs are included in the media attribute ordered by priority?

Options

AG.711ulaw, G.722, G.711alaw, and G.729
BG.711alaw, G.711ulaw, G.729, and G.722
CG.722, G.711alaw, G.729, and G.711ulaw
DG.711ulaw, G.711alaw, G.722, and G.729

Explanation

In an SDP 'm=' line, the codecs are listed as payload types (PT) in order of preference, and these payload types map to specific codecs defined in the 'a=rtpmap' lines. Assuming a common SDP snippet, the codecs are ordered as G.711ulaw, G.711alaw, G.722, and G.729.

Common mistakes.

A. This order is incorrect based on the typical priority given to PT 0 (G.711ulaw) and the likely order in an SDP.
B. This order is incorrect; G.711alaw (PT 8) usually follows G.711ulaw (PT 0) in preference.
C. This order is incorrect; G.722 (PT 9) is typically lower priority than G.711 codecs.

Concept tested. SDP codec negotiation and priority

Reference. https://www.rfc-editor.org/rfc/rfc3551

Topics

#SDP#Codecs#Media Negotiation#Codec Priority

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