Re: [AVT] What is an RTP Session?

[Pekka Pessi <Pekka.Pessi@nokia.com>]

Mike Taylor <mtaylor_eng@hotmail.com> writes:
>I'm an RTP newbie and I'm trying to understand just what constitutes
>an RTP session when the participants are using unicast rather
>than multicast.  I find the description in RFC 1889 quite ambiguous.

	The description basically states that a group of participants
	sending RTP to a multicast address is one session identified by
	the destination address/port pair, but unicast streams can also
	be one session regardless of the destination address/port pairs. 
	The RFC1889 definition requires that all the recipients have
	common port number, but this limitation is lifted in rtp-new
	draft.

	Basically the pure unicast case boils down to two peers sending
	media to each other; they are in a single session and can send
	combined SR/RR RTCP packets to each other.

	A configuration where one participant is receiving multiple
	unicast streams and sending RTP/RTCP via multicast is also one
	session.

	Rule of thumb here is that if a participant can send all its
	RTCP packets to a single destination address, it is in one
	session.

	From the programming point-of-view, a RTP session participant
	always have four sockets: one for receiving RTP with recv(),
	second for sending RTP with send(), third for receiving RTCP
	with recv(), fourth for sending RTCP with send(). The sockets
	used for sending are always connected() to certain address, the
	sockets used for receiving are always bound. If the participant
	must change these sockets, he is moving to another session. 
	(The second socket is optional, if you do not send any
	media).

					Pekka
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