Re: [rtcweb] Consent freshness - revisiting the RTCP option

Harald Alvestrand <harald@alvestrand.no> Wed, 09 May 2012 09:59 UTC

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Date: Wed, 09 May 2012 11:59:47 +0200
From: Harald Alvestrand <harald@alvestrand.no>
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To: "Muthu Arul Mozhi Perumal (mperumal)" <mperumal@cisco.com>
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Subject: Re: [rtcweb] Consent freshness - revisiting the RTCP option
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On 05/09/2012 09:34 AM, Muthu Arul Mozhi Perumal (mperumal) wrote:
> More reasons why RTCP may not be suitable for consent freshness:
> 1. RTCP (as described in RFC3550) is receiver based, so the browser
> can't explicitly request for consent. If consent freshness fails (for
> e.g, RTCP packets temporarily lost because of network flapping), the
> browser would have to wait for the peer to send RTCP before it can start
> transmitting media. Worst, if the peer isn't an active sender it may not
> send any RTCP RR until it receives media. It could send a bare minimum
> RTCP RR (an RR with RC=0 and SDES with CNAME), but that has zero
> entropy:
> http://www.ietf.org/mail-archive/web/rtcweb/current/msg01497.html
Of course endpoints are expected to be RFC 3550 compliant, which 
includes obeying the diktat of section 6.3.5: "Every SSRC that hasn't 
sent an RTP or RTCP packet for 5*5 seconds is dead".
> 2. There are still some endpoints that don't send / pay attention to
> RTCP:
> http://www.ietf.org/mail-archive/web/rai/current/msg01257.html
>
> For these cases an intermediary like an SBC would have to manufacture
> them. Manufacturing them for just consent freshness would be expensive
> compared to generating STUN request/response.

For non-RTCP entities, we need an RTCP-generating gateway in order to 
interwork.
End of story.
(My opinion.)