Hi there RFC3551 (section 4.5.3) and RFC3555 (section 4.1.3) seem rather clear on the matter.
G723 can be encoded at 5.3 or at 6.3, and (unless restricted as in the examples below) the media engine should handle changing of bitrate on the fly at each 30ms boundary depending on the 2 least-significant-bits of the first octet of each 30ms frame. AnnexA can also be specified for the Silence Insertion Descriptor (voice activity detection), and again should be handled on the fly in the same way. So: a 30ms frame at 6.3 would be a 24-octet frame with the 2 least-significant-bits of the first octet == 00 a 30ms frame at 5.3 would be a 20-octet frame with the 2 least-significant-bits of the first octet == 01 a 30ms frame denoting SID would be a 4-octet frame with the 2 least-significant-bits of the first octet == 10 I think that the following examples would be correct: Case 1: Both Bit-rates possible, plus AnnexA support --- m=audio 9012 RTP/AVP 4 a=fmtp:4 annexa=yes Case 1a: Both Bit-rates possible, plus AnnexA support (but since AnnexA support is enabled by default, we do not need to specify it) --- m=audio 9012 RTP/AVP 4 Case 2: Both Bit-rates possible, WITHOUT AnnexA support --- m=audio 9012 RTP/AVP 4 a=fmtp:4 annexa=no Case 3: Bit-rate 5.3 only, plus AnnexA support --- m=audio 9012 RTP/AVP 4 a=fmtp:4 bitrate=5.3; annexa=yes Case 3a: Bit-rate 5.3 only, plus AnnexA support (but since AnnexA support is enabled by default, we do not need to specify it) --- m=audio 9012 RTP/AVP 4 a=fmtp:4 bitrate=5.3 Case 4: Bit-rate 6.3 only, WITHOUT AnnexA support --- m=audio 9012 RTP/AVP 4 a=fmtp:4 bitrate=6.3; annexa=no Could someone please confirm if my understanding is correct? Kevin Attard Compagno 3CX - www.3cx.com Developers of 3CX Phone System - a software based VoIP PBX On 27 February 2010 05:02, Ronak Shah <[email protected]> wrote: > Dear elision, > > Is any device provide this type of configuration check it out what other > product are doing for this? > > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of > Elison > Niven > Sent: Thursday, February 25, 2010 6:12 PM > To: [email protected] > Subject: [Sip-implementors] G723.1 H and G723.1 L SDP negotiation (yet > again) > > Hi List, > > I know this has been discussed and asked a lot of times in the past but > still I find no affirmative solution. > > For a UA that supports both G7231-H and G7231-L, SHOULD it specify both the > codecs in the offer that it sends? > > If the UA is willing to specify both the codecs in the offer that it sends > (because it specifies two different codecs in its user interface), what > should be the method of specifying the codecs in the SDP body? > > I find two possible ways of specifying both the codecs in the offer: > > Case 1: Both codecs use different payload types, one of them uses a dynamic > payload type. > > m = audio 8000 RTP/AVP 4 97 > m = rtpmap:4 G723/8000 > m = fmtpmap:4 bitrate=5.3 > m = rtpmap:97 G723/8000 > m = fmtpmap:97 bitrate=6.3 > > Case 2: Both codecs use the same static payload type. > > m = audio 8000 RTP/AVP 4 4 > m = rtpmap:4 G723/8000 > m = fmtpmap:4 bitrate=5.3 > m = rtpmap:4 G723/8000 > m = fmtpmap:4 bitrate=6.3 > > Which of the above SDP offers seems valid? > > Suppose I receive an answer from UA2 to the offer in Case 1 as: > > m = audio 8000 RTP/AVP 4 > m = rtpmap:4 G723/8000 > m = fmtpmap:4 bitrate=5.3 > > What should be the payload of the packets that UA2 sends? Should it be 4 or > 97? > > Best Regards, > Elison > > > > > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > > > Email Scanned for Virus & Dangerous Content by : www.CleanMailGateway.com > > > > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
