Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)
Randell Jesup <randell-ietf@jesup.org> Mon, 19 September 2011 07:55 UTC
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Date: Mon, 19 Sep 2011 03:54:44 -0400
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Cc: Randell Jesup <randell-ietf@jesup.org>, rtcweb@ietf.org
Subject: Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)
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Open question to the list: should the congestion-control-geeks discuss here on the list the nitty-gritty details required to build the requirements and especially to design and debate a possible proposed "baseline" congestion-control algorithm? We can certainly do that detailed discussion by email and come back with a draft; I had been planning to do it by email, but recent discussion on rtcweb made me think I should ask for opinions on this. Given the structure, if there's any significant support for "on-the-list" I'll do that. Realize though that they may get pretty long and detailed without really touching on the larger issues being discussed here. Right now the bof members to discuss this and propose a draft would be myself, Harald, Justin, Stefan Holmer and Magnus. On 9/19/2011 3:06 AM, Stefan Holmer wrote: > On Mon, Sep 19, 2011 at 12:10 AM, Randell Jesup > <randell-ietf@jesup.org <mailto:randell-ietf@jesup.org>> wrote: > > On 9/16/2011 9:26 AM, Magnus Westerlund wrote: > > 1. Section 3: As delay based congestion control has been tried > a number > of times and meet with less than stellar success I wonder if > you have > any understanding of how this relates to the issues previously > encountered: > > Do you have any pointers to these earlier attempts? My separate > experience > with this class has been extremely successful, though perhaps with > a set of > real-world use-cases that don't cover the situations you're > referring to. > My understanding is that Radvision's NetSense is very similar from > their > description of it. > > > I'm interested in any references you may have as well. I doubt you'll find many/any, as the first published discussion I saw of delay-sensing congestion control for RTP data was Radvision's posts about Netsense last year and in their Android webcasts; and that was pretty detail-free until their recent blog posts. There's plenty of un-published experience with them at various companies I believe.... Not just Google and Radvision. > > - Stability (especially on short RTTs) > - How it competes with TCP flows, which was a real issues for > TCP Vegas > but may be less of an issue here. > > Perhaps Google can comment here about what tests they've done. If > anything, > this class of algorithm when faced with aggressive TCP flows will > eventually > have problems, because TCP will tend to fill up the buffers at the > bottleneck. > Since this algorithm senses buffers starting to fill up, it will > tend to back > off before TCP is likely to see a loss event. Now, it's more > complex than > that of course, and multiple flows make it more complex still. > It's also > sensitive to the adaptation rate of this algorithm and speed of > backoff. > If I remember, TFRC tends to back off more slowly than TCP but > also increase > more slowly; I suspect Google's algorithm is similar. > > > As you're saying, it will always be hard for delay based congestion > control algorithms to compete with a packet loss based algorithm. The > delay based algorithm will detect over-use much earlier than the > packet loss based one, and that's basically what we've seen in the > tests we've been running as well. I do think we would benefit from > more tests in this area. For instance, we might want to go with an > additive increase approach rather than the current one which is > multiplicative, this would likely help improve the algorithms self > fairness as well. Probably; additive increase is probably better, or possible using a fraction-of- predicted-bandwidth increase. If you use additive increase, it should probably be partly proportional to the maximum "good" bandwidth seen during the connection. This provides some needed scaling of the ramp-up rate to the absolute magnitude of bandwidth available. -- Randell Jesup randell-ietf@jesup.org
- [rtcweb] An input for discussing congestion contr… Harald Alvestrand
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Harald Alvestrand
- Re: [rtcweb] An input for discussing congestion c… Magnus Westerlund
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Stefan Holmer
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Henrik Lundin
- Re: [rtcweb] An input for discussing congestion c… Varun Singh
- Re: [rtcweb] An input for discussing congestion c… Henrik Lundin
- Re: [rtcweb] An input for discussing congestion c… Tim Panton
- Re: [rtcweb] An input for discussing congestion c… Henrik Lundin
- Re: [rtcweb] An input for discussing congestion c… Varun Singh
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Soo-Hyun Choi
- Re: [rtcweb] An input for discussing congestion c… Henrik Lundin
- Re: [rtcweb] An input for discussing congestion c… Soo-Hyun Choi
- Re: [rtcweb] An input for discussing congestion c… Harald Alvestrand
- Re: [rtcweb] An input for discussing congestion c… Soo-Hyun Choi
- Re: [rtcweb] An input for discussing congestion c… Harald Alvestrand
- Re: [rtcweb] An input for discussing congestion c… Dzonatas Sol
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Soo-Hyun Choi
- Re: [rtcweb] An input for discussing congestion c… Harald Alvestrand
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Jim Gettys
- Re: [rtcweb] An input for discussing congestion c… Henrik Lundin
- Re: [rtcweb] An input for discussing congestion c… Ingemar Johansson S
- Re: [rtcweb] An input for discussing congestion c… Henrik Lundin
- Re: [rtcweb] An input for discussing congestion c… Randell Jesup
- Re: [rtcweb] An input for discussing congestion c… Stefan Holmer
- Re: [rtcweb] An input for discussing congestion c… Soo-Hyun Choi