Related specifications
RFC 3389, RTP Payload for Comfort Noise (CN), available at http://www.ietf.org/
RFC 3551, RTP Profile for Audio and Video Conferences with Minimal Control, available at http://www.ietf.org/
RFC 4867, RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs, available at http://www.ietf.org/
Implementation notes
Generic comfort noise support with G.711 (PCMA & PCMU) and G.726 codecs is provided, (RFC 3389.)
Generic comfort noise is supported with iLBC. (RFC 3389.)
Update interval for generic CN depends on the codec used. The CN update occurs when the encoder detects significant changes in the background noise resulting in the implementation generating and sending an updated CN RTP packet.
Generic comfort noise usage with AMR is not supported, as the AMR codec itself contains a method for comfort noise/silence suppression that can be signalled inband if VAD is enabled.
Generic CN usage with G.729 is not supported, instead G.729 Annex B is used. (RFC 3551.)