[asterisk-dev] queries regarding SDP implementation for multiple bit rates for g.722 codec.

Kevin P. Fleming kpfleming at digium.com
Mon Aug 6 10:01:36 CDT 2007

lalit kumar wrote:

> As we know that g.722 supports 48,56 and 64 kbps.

Sort of... It supports using 8kbps or 16kbps of the stream as a data
channel. The stream is always 64kbps, but may contain fewer bits of
audio data.

> Query-1: à I want to negotiate g.722 codec with multiple bitrates 64
> 56,and 48. Then what would be SDP attributes value in Sip invite.

RFC3551 makes no accommodation for the various G.722 audio/data channel
modes. I do not see (in a quick Google search) where using these modes
has ever been specified over RTP, or to be signaled in SDP.

> Query-3 à On network what flavor of G.722 codec is better from 64, 56
> and 48 kbps?

It makes no difference because the media stream is always 64kbps. The
only reason to use the other modes is if you want to transmit a data
channel between the endpoints as part of the media stream.

Kevin P. Fleming
Director of Software Technologies
Digium, Inc. - "The Genuine Asterisk Experience" (TM)

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