Hello, RTP Dynamic Payload and Static Payload
Static payload is payload which is defined in the IANA rtp parameter document An example of a static payload type is a-law PCM coded single channel audio sampled at 8KHz. This is completely defined in the RTP Audio/Video profile as payload type 8, so the media field for such a stream sent to UDP port 47232 is: m=video 47232 RTP/AVP 8 For static payloads the a=rtpmap line is not mandatory in SDP, considering that the payload type itself can specify unique audio encoding An example of a dynamic payload type is 18 bit linear encoded stereo audio sampled at 18KHz. If we wish to use dynamic RTP/AVP payload type 99 for such a stream, additional information (a=rtpmap line) is required to decode it: m=video 39132 RTP/AVP 99 a=rtpmap:99 L18/16000/2 The format is a=rtpmap:payload type encoding name/clock rate/encoding parameters in this rtpmap we are mapping a codec (encoding name) with the payload number as it does not have a rtp payload number allocated by IANA rfc3551 defines codec names which can be used in SDP while IANA maps codecs names to a number known as payload number ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Registry: PT encoding name audio/video (A/V) clock rate (Hz) channels (audio) Reference -------- -------------- ----------------- --------------- ---------------- --------- 0 PCMU A 8000 1 [RFC3551] 1 Reserved 2 Reserved 3 GSM A 8000 1 [RFC3551] 4 G723 A 8000 1 [Kumar] 5 DVI4 A 8000 1 [RFC3551] 6 DVI4 A 16000 1 [RFC3551] 7 LPC A 8000 1 [RFC3551] 8 PCMA A 8000 1 [RFC3551] 9 G722 A 8000 1 [RFC3551] 10 L16 A 44100 2 [RFC3551] 11 L16 A 44100 1 [RFC3551] 12 QCELP A 8000 1 13 CN A 8000 1 [RFC3389] 14 MPA A 90000 [RFC3551][RFC2250] 15 G728 A 8000 1 [RFC3551] 16 DVI4 A 11025 1 [DiPol] 17 DVI4 A 22050 1 [DiPol] 18 G729 A 8000 1 19 Reserved A 20 Unassigned A 21 Unassigned A 22 Unassigned A 23 Unassigned A 24 Unassigned V 25 CelB V 90000 [RFC2029] 26 JPEG V 90000 [RFC2435] 27 Unassigned V 28 nv V 90000 [RFC3551] 29 Unassigned V 30 Unassigned V 31 H261 V 90000 [RFC4587] 32 MPV V 90000 [RFC2250] 33 MP2T AV 90000 [RFC2250] 34 H263 V 90000 [Zhu] 35-71 Unassigned ? 72-76 Reserved for RTCP conflict avoidance [RFC3551] 77-95 Unassigned ? 96-127 dynamic ? [RFC3551] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Regards! Valdemar -----Original Message----- From: sip-implementors-boun...@lists.cs.columbia.edu [mailto:sip-implementors-boun...@lists.cs.columbia.edu] On Behalf Of ext Saúl Ibarra Corretgé Sent: Monday, November 29, 2010 10:32 AM To: Iñaki Baz Castillo Cc: sip-implementors@lists.cs.columbia.edu Subject: Re: [Sip-implementors] dynamic payload negotiation >> Can you provide a reference to this? Is it really allowed? > > Yes it is. Each direction of the stream can epecify its own payload > types even for same codec. Also note that a stream could use codec A > in left direction and codec B in right direction. > My question was not regarding the possibility of asymmetric negotiation, but regarding the use of a static assigned payload codec with a dynamic one. In other words, is this allowed? a=rtpmap: 97 PCMA/8000 Thanks and regards, -- /Saúl http://saghul.net | http://sipdoc.net _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
