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@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@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@ietf.org Reply-To: internet-drafts@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-breake...
-- Colin Perkins http://csperkins.org/
_______________________________________________ Audio/Video Transport Core Maintenance avt@ietf.org https://www.ietf.org/mailman/listinfo/avt