[R-C] [AVTCORE] Fwd: I-D Action: draft-perkins-avtcore-rtp-circuit-breakers-00.txt

[Mark Handley]

Colin, Varun,

Can you clarify how the circuit breaker mechanism would work with RFC
4585 extended feedback.  To make things concrete, I'm thinking about
the following scenario:

 - Sender is sending 2Mb/s video into a 4Mb/s DSL line.  RTT is 100ms.
 - Receiver is allowed to send up to 2.5% of this as RTCP feedback in
ACK mode, so that's 6.5 packets per RTT if I got the maths right.
 - A TCP flow slowstarts, doubles the window for the last time and
collides with the RTP flow in the wonderful way slowstart sometimes
does.  If you're unlucky, you'll get 33% packet loss for one full RTT
before TCP backs off.
 - The RTCP receiver sends 6 successive RTCP reports over one RTT
indicating 33% loss.  If doesn't really matter if ACKs or NACKs are
sent in this scenario.

The calculated TCP rate would be ~18Kb/s for those parameters, so the
circuit breaker would kick in if I understood the draft correctly
because that's more than two reporting intervals with excessively high
loss.

This is the main reason for loss event rate in the TFRC specification
- you avoid responding to such transients too strongly.

Cheers,
Mark



On 5 March 2012 23:32, Colin Perkins <csp at csperkins.org> wrote:
> Here's our initial attempt at a "circuit breakers" draft for RTCWeb. Comments welcome - this is very much a straw-man for discussion, rather than a final solution.
>
> Colin
>
>
>
> Begin forwarded message:
>> From: internet-drafts at ietf.org
>> Subject: I-D Action: draft-perkins-avtcore-rtp-circuit-breakers-00.txt
>> Date: 5 March 2012 20:17:59 GMT
>> To: i-d-announce at ietf.org
>> Reply-To: internet-drafts at ietf.org
>>
>>
>> A New Internet-Draft is available from the on-line Internet-Drafts directories.
>>
>>       Title           : RTP Congestion Control: Circuit Breakers for Unicast Sessions
>>       Author(s)       : Colin Perkins
>>                          Varun Singh
>>       Filename        : draft-perkins-avtcore-rtp-circuit-breakers-00.txt
>>       Pages           : 14
>>       Date            : 2012-03-05
>>
>>   The Real-time Transport Protocol (RTP) is widely used for telephony,
>>   video conferencing, and telepresence applications.  These
>>   applications are often used over best-effort UDP/IP networks.  If
>>   congestion control is not implemented then network congestion will
>>   deteriorate the user's multimedia experience.  This document does not
>>   propose a congestion control algorithm.  Instead, it specifies a
>>   minimal set of "circuit-breakers".  Circuit-breakers are conditions
>>   under which an RTP flow should cease to transmit media to protect the
>>   network from excessive congestion.  It is expected that all RTP
>>   applications running on best-effort networks will be able to run
>>   without triggering these circuit breakers in normal operation.
>>
>>
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-perkins-avtcore-rtp-circuit-breakers-00.txt
>
> --
> Colin Perkins
> http://csperkins.org/
>
>
>
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