Re: [AVT] RFC3550 RTP Session defintion Qi

[Stephen Casner <casner at acm.org>]

On Thu, 12 Aug 2004, Vivek Mudgil wrote:

> Whatever you have stated is right. You have considered the two cases.
> The second case is valid with multicast conference or with Unicast
> conference using the same RTP port pair to send and receive data from
> other participants.

The second case is also valid if each participant uses distinct port
pairs to receive data from other participants.  Why do you think
otherwise?

> The first case will always result into three separate multiparty
> sessions is [if?] separate RTP unicast port pair is used to receive
> data from the other two participants.

Why always?

> 1) Consider the unicast conference between three parties each using
> separate RTP port pair to establish RTP session with each. In this
> case each RTP port pair session will send the RTCP report to the one
> participant from which it is receiving data and not to the other
> participant who is sending the data to the other RTP port pair.

The RTCP report could be sent to the both other participants.  It
makes no difference if the other participants are both receiving RTCP
on the same port or different ports.  As the examples in the RFC text
are attempting to explain, it is this choice (whether to send to only
one participant or to all of them) that determines whether there is
one RTP session or multiple RTP sessions.

> Hence a single RTP session should not be possible using distinct
> pair of ports in receive data from other participants in unicast
> mode.

No, as explained above.

> If this is correct then it contradicts the following line.
>
>       "In the unicast case, a participant may
>       receive from all other participants in the session using the same
>       pair of ports, or may use a distinct pair of ports for each."
>
> Kindly let me know if I am missing something.

You make an assumption about how RTCP can be sent, but I don't see the
justification for that assumption.

                                                        -- Steve

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