This is certainly possible, even though the draft doesn't state it explicitly, provided both the loopback-source and loopback-mirror are capable of sending and receiving the same codec using different RTP payload types.
However, the answer from the loopback-mirror can indicate a different payload type other than what was specified in the "a=loopback-source" line -- in that case the loopback-source MUST send using the payload type received in the answer, as specified in section 5.4 of the draft. Muthu On Wed, Aug 4, 2010 at 12:32 PM, Bharat S <[email protected]> wrote: > HI all, > I have a question on SIP Media Loopback > > The SDP format for a SIP Endpoint initiating a loop back call appears as > below. > ( As per the draft > http://tools.ietf.org/html/draft-ietf-mmusic-media-loopback-14) > > m=audio 41352 RTP/AVP 0 8 100 > a=loopback:rtp-media-loopback > a=loopback-source:0 8 100 > a=rtpmap:0 pcmu/8000 > a=rtpmap:8 pcma/8000 > a=rtpmap:100 G7221/16000/1 > > As seen above, two lines ( m line and a=loopback-source) carry the RTP > payload > types. When loopback-mode is specified as loopback-source, the media format > corresponds to the RTP payload types thesource is willing to send. When > loopback-mode is specified as loopback-mirror, the media format corresponds > to > the > > RTP payload types the mirror is willing to receive. The payload types > specified > in m= line for a loopback-source specify the payloads the source is willing > to > receive. > > The question is what does it mean if the payload type numbers in m= line > and > loopback-source line are different as below? > > m=audio 41352 RTP/AVP 112 113 > a=loopback:rtp-pkt-loopback > a=loopback-source:0 8 > a=rtpmap:112 encaprtp/8000 > a=rtpmap:113 rtploopback/8000 > > Can any SIP endpoint ever receive media on some payload types and send > media on > a different payload type? The draft doesn't speak much about such a > scenario. > > Many Thanks, > Bharat > > > > _______________________________________________ > 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
