Re: [Sip-implementors] Silence Suppression for G711

[Jan Bollen]

Hi Sunil,  For G.729, use the annexb=yes. It is the codec specific value for silence suppression. For G.711 there is no codec specific VAD. So if a=silenceSupp is not used the offer indicates that G.729 is using silence suppresion and G.711 not. Provided that the voice gateway or CPE isn't applying a general VAD mechanism to its VoIP configuration. Now, the idea might be to specify different parameters for various codecs in one media section. Maybe RFC 6871 might be your friend: it introduces a new attribute ("a=mfcap") that specifies media format parameters associated with one or more media format capabilities. Else ask the experts on the mmusic mailing list... cheers,  jan On 13/11/2013 17:36, jcsunil1 wrote: Thanks jan.then in that case, how do we tell to other end that silence suppression  is supported in G729 and not in G711.  What I mean is , is it possible to specify codec specific value for silence suppression in Invitr -------- Original message -------- From: Jan Bollen Date:13/11/2013 9:59 PM (GMT+05:30) To: J C Sunil Kumar Reddy Cc: sip-implementors@lists.cs.columbia.edu Subject: Re: [Sip-implementors] Silence Suppression for G711 Hi, I would think that the a=silenceSupp attribute line applies to the whole media section and not to just one codec. If the SDP body does contain the "annexb=yes" attribute, the codec built-in silence suppression mechanism is used (if the peer UA agrees to use this type of codec) else the a=silenceSupp is applied, which might be an external VAD mechanism. When the a=silenceSupp is absent, the external, UA specific silence suppression mechanism can also be used. cheers,  jan On 13/11/2013 14:37, J C Sunil Kumar Reddy wrote: Hi, How to say to other end that Silence Suppression is supported in G729 and not supported in G711? Because if annexb is not present in SDP for G729, then it means that Silence Suppression is supported(i dont know why it is reverse). putting like this below will work In the INVITE ? m=audio 49152 RTP/AVP 0 18 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:18 G729/8000 a=rtpmap:8 PCMA/8000 a=silenceSupp:off------- a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=silenceSupp:off------- attribute is global for all codec's or only for the last rtpmap before it ? Regards, Sunil _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors

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