RE: [AVT] RFC3550 RTP Session defintion Qi

[Stephen Casner <casner at acm.org>]

To close off this thread, let me mention that Oren Peleg sent a
private reply to say that he understood what I was saying about RTP
sessions after considering that the same RTCP report is sent to all
participants in a shared session.

To be fair, this is a rather subtle issue that we authors and
designers of RTP did not understand correctly when RFC 1889 was
written.  That first version of the spec defined the RTP session by
the destination port pair (RTP+RTCP) and required that a participant
use the same destination port to receive packets from all other
participants in a multi-party unicast RTP session.

At the 41st IETF in Los Angeles in April, 1998, Marcel Graf asked me
about the number of RTP sessions in a multi-unicast scenario because
this was unclear in the context of H.323 session setup.  It was not
until relatively late in the editing of the spec for RFC 3550 that we
discussed the current RTP session definition at some length.  It
became clear to me that "the distinguishing feature of an RTP session
is that each maintains a full, separate space of SSRC identifiers" and
that the underlying use of multicast with a common port pair or
unicast with different port pairs did not matter.

                                                        -- Steve

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