350-801 · Question #442
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?
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.
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?
Exhibit
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
How the community answered
(47 responses)- A2% (1)
- B2% (1)
- C4% (2)
- D91% (43)
Why each option
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.
This order is incorrect based on the typical priority given to PT 0 (G.711ulaw) and the likely order in an SDP.
This order is incorrect; G.711alaw (PT 8) usually follows G.711ulaw (PT 0) in preference.
This order is incorrect; G.722 (PT 9) is typically lower priority than G.711 codecs.
The 'm=audio' line in an SDP message lists payload types in order of preference. A typical priority order for common codecs is PT 0 (G.711 ulaw), PT 8 (G.711 alaw), PT 9 (G.722), and PT 18 (G.729), which corresponds to the list G.711ulaw, G.711alaw, G.722, and G.729.
Concept tested: SDP codec negotiation and priority
Source: https://www.rfc-editor.org/rfc/rfc3551
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