RTCP sender reports - when to use?

Orit Levin orit at radvision.com
Thu Sep 16 16:30:22 EDT 1999

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
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?

>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)?

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