Subject: [AVT] Question for ECN solution for RTP session

From: Zhu Lei <[email-masked]>
Date: Fri, 29 Jan 2010 16:47:14 +0800

Hi all,
 
May I ask authors of ECN draft for RTP a question. 
 
I was known recently that the RTCP bandwidth could be negotiated as "0"
during RTP session establishment. Therefore, seems that RTCP packet do not
exist during a RTP session.
 
Is this a problem of this draft as RTCP to notify congestion does not exist?
Thanks.
 
Best regards,
Lei Zhu

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From: Magnus Westerlund <[email-masked]>
Date: Fri, 29 Jan 2010 10:08:09 +0100

Zhu Lei skrev 2010-01-29 09:47:
> during RTP session establishment. Therefore, seems that RTCP packet do
> not exist during a RTP session.
>  
> Is this a problem of this draft as RTCP to notify congestion does not
> exist? Thanks.
>  

Yes, you can negotiate RTCP bandwidth to 0, however that is not possible
to combine with ECN for RTP as it requires RTCP.

Section 4.3.2 of the draft does have the following text:

It is
   important to configure the RTCP bandwidth (e.g. using an SDP "b="
   line) such that the bit-rate is sufficient for a usage that includes
   these regular summary and none reports, and feedback on ECN-CE
   events.

Configuring it to 0 is obviously not meeting the goals. Maybe we should
use some normative text, but it seemed obvious to us authors that you
require RTCP with sufficient bandwidth for ECN for RTP to work.

Cheers

Magnus Westerlund
(As individual)

IETF Transport Area Director
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