[SIPForum-discussion] G729 and G279 AB - audio quality issues

Gast, Jim jim.gast at tdstelecom.com
Mon Jun 17 14:58:07 UTC 2013

Hi, Raghul –

Implementations of G.729 that do not OFFER annex-B do not do Voice Activity Detection (VAD) and never generate CN (Comfort Noise) RTP packets.  But the can generate comfort noise if they receive a CN packet.  Generating CN is easy and takes almost no memory space.  Listening for voice activity and keeping track of inactivity is a somewhat independent feature.

The way I read the spec, all of the rtpmap:18 (G.729 with our without annex A or annex B) are seamlessly interoperable.  If one side says that it is using annex A, that just tells the other side that he is using “reduced complexity” to do the compression, but there is NO DIFFERENCE in the decompression algorithm.  The same is true for annex B.  One side can say, “a=fmtp:18 annexb=yes” to tell the other side that (s)he intends to send CN packets.  The other side might ignore the CN packets without (from my reading) violating the spec.

To get a great answer, ask https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors.


/ Jim

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Raghul Prasanna
Sent: Sunday, June 16, 2013 5:07 AM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] G729 and G279 AB - audio quality issues

Hello All,

If A end supports G729 and B says G729 AB, will there be any call quality issues?

I believe the A end wont be able to handle silence packet and should discard them, apart from that the real audio should remain intact and so no impact on call quality. Please let me know your thoughts.

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