Hi Paul SDP used by SIP contains the connection address in the 'c=' line, while it contains the RTP port information in 'm = ' line. the RTCP port used will be RTP port +1
c=<network type> <address type> <connection address> m=<media> <port> <transport> <fmt list>
The call originator will sends it's RTP port information & connection address in the INVITE message, and it will get the other end RTP port info & connection address in the response ( e.g.200 OK).
Thanks & Regards, Hemant Agrawal
Folks,
I was recently pondering issues related to H.323/SIP interworking-- particularly the handling of media streams.
If I understand things correctly, the 'm=' line in the SDP used by SIP indicates only the media address to which RTP packets will be sent. It
says
nothing about the RTP/RTCP port used for sending media. Those can be another pair of ports, apparently.
How, then, can an H.323 IWF send an OLC to an H.323 endpoint? (Let's
assume
that the IWF does not want to proxy the media-- only handle signaling.)
Assume that the IWF has received the INVITE message, containing the RTP address of the reverse channel. It then goes ahead and establishes the
call
with the H.323 endpoint, starts H.245 and exchanges capability
information.
Suppose the IWF now wishes to open a channel. Part of the forwardLogicalChannel parameters of the OLC is a required field called "mediaControlChannel". However, this information is not passed in the
SDP.
Are people assuming, as I had done, that the 'm=' line contained the RTP address for both sending and receiving media?
Am I misreading something or is there a real interworking issue here?
Thanks, Paul
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