RTCP sender reports - when to use?

Dave Walker dave_walker at Mitel.COM
Fri Sep 17 11:35:29 EDT 1999

Hi Orit,

What you describe seems like the correct behaviour, is it documented
anywhere, or is it a candidate for the Implementors Guide?


Dave Walker
Mitel Corporation
Ontario, CANADA

Orit Levin wrote:
> Hi Henri!
> The answer is ... the RTCP channel is bi-directional even when opened to be
> used for A->B RTP media stream only.
> If A wants to send a stream going A->B, A originates the OLC procedure.
> During this procedure B's  RTP port, B's RTCP port and A's RTCP ports are
> exchanged between the sides.
> For the same "kind" of media stream (such as "voice" or "video) usually B
> would like to send a media stream going A<-B belonging to the same H.245
> session opened above. In this case B will issue OLC advertising the same B's
> RTCP port already used within this session.
> As the result, two media unidirectional RTP channels and a single common
> bi-directional RTCP channel will be opened within the same H.245 session.
> Best Regards,
> Orit Levin
> RADVision Inc.
> 575 Corporate Drive Suite 420
> Mahwah, NJ 07430
> Tel: 1 201 529 4300  (230)
> Fax: 1 201 529 3516
> www.radvision.com
> orit at radvision.com
> -----Original Message-----
> From: henri.maenpaa at NOKIA.COM <henri.maenpaa at NOKIA.COM>
> Date: Thursday, September 16, 1999 5:05 AM
> Subject: RTCP sender reports - when to use?
> >Hi,
> >
> >Could somebody clarify a few things for me...
> >
> >Say, there's a call between A and B in H.323. RTP sessions for both stream
> >directions are totally independent of each other, right? (except with T.120
> >channel a bidirectional one can be used).
> >
> >Let's concentrate on RTP session where stream goes from A to B.
> >This one RTP session is a unidirectional channel. Is the related RTCP
> >channel also a unidirectional channel, but to opposite direction?
> >So, if this is true, how can we use sender reports (SR) in H.323?
> >Am I right when I assume that only way sender reports can be used in H.323
> >is with a T.120 bidirectional channel (when RTCP channel would probably be
> >bidirectional also)?
> >
> >Cheers,
> >Henri
> >

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