SIP and H.323 Interworking question
Paul E. Jones
paulej at PACKETIZER.COM
Wed Sep 13 21:28:11 EDT 2000
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?
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