Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)
Henrik Lundin <hlundin@google.com> Tue, 20 September 2011 05:56 UTC
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References: <4E649FBD.1090001@alvestrand.no> <4E734E89.5010105@ericsson.com> <4E766C4C.2020201@jesup.org> <CAEdus3LcjV9x+gLdZm5vwKhh-ge6xzfWSEB_NxcHe1Gz_5DZ8g@mail.gmail.com> <CAOhzyf=MqsgsGUi521oJ5N6+T+K1N01MjeHYPpX_VZK8uyQksw@mail.gmail.com> <CAKkvrEkx0mqnDWqNYse3r9WUMbYKNZhrBqQ0SPUAnTtKrA5bLg@mail.gmail.com>
Date: Tue, 20 Sep 2011 07:58:49 +0200
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From: Henrik Lundin <hlundin@google.com>
To: Soo-Hyun Choi <soohyun.choi@cl.cam.ac.uk>
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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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On Tue, Sep 20, 2011 at 7:37 AM, Soo-Hyun Choi <soohyun.choi@cl.cam.ac.uk>wrote: > A question and a suggestion. > > > > >>>> > >>>> 4. Section 4. > >>>> > >>>> "This algorithm is run every time a receive report arrives at the > >>>> sender, which will happen [[how often do we expect? and why?]]. If > >>>> no receive report is recieved within [[what timeout?]], the > algorithm > >>>> will take action as if all packets in the interval have been lost. > >>>> [[does that make sense?]]" > >>>> > >>>> The transmission of receiver reports is highly dependent on RTP > profile, > >>>> the RTCP bandwidth, trr-int parameter and any feedback events. > >>>> > >>>> If I start with assuming AVPF which seems reasonable in most browser > to > >>>> browser case with our current proposals for RTP support. Then if there > >>>> are no feedback events the transmission of receiver reports will occur > >>>> as often as the bandwidth allows, but no more often than the value of > >>>> trr-int parameter. > >>>> > >>>> Here is might be worth mentioning that I do expect trr-int to be set > to > >>>> avoid RTCP reporting to often due to the relatively high RTCP > bandwidth > >>>> values that will be set due to the multiplexing of audio and video in > a > >>>> single RTP session. Thus avoiding that RTCP rates are as high or > larger > >>>> than the audio streams they report in steady state. > >>> > >>> Agreed. This is where my plans to suggest a baseline algorithm that > >>> melds > >>> the reception data of all the streams in the PeerConnection may be a > >>> significant advantage over doing bandwidth estimation on each stream > >>> independently. We'll see if I can make the idea work, but there are > some > >>> significant advantages if it does. If not, we can estimate in each > >>> channel > >>> independently as per the Google algorithm. > >>> > >>> You can also use rtcp-fb PLI/etc events to hang these reports off of, > >>> increasing > >>> the frequency they get through with minimal extra bandwidth use. > >>> > >>> > >>>> When feedback events occur the stack will have the choice of sending a > >>>> RTCP RR, that is a choice provided due to the reduced size RTCP > >>>> specification included. But if the loss cumulative count diff is > >>>> non-zero it might be worth mandating that the RR/SR is included in any > >>>> such feedback RTCP packet. > >>> > >>> Exactly - or a TMMBR with the results of the receiver-side bandwidth > >>> calculations. > >>> > >>>> For that reason causing a feedback event when there is losses and > >>>> schedule them using the early algorithm may be a good choice to ensure > >>>> timely reporting of any loss. > >>>> > >>>> If one uses AVP then the RTCP timing rules will give you when you > >>>> transmit RTCP feeedback and thus the parameterization becomes central > >>>> here. A clear issue is if people uses the minimal interval of 5 > seconds > >>>> or the 360/Session_BW(in kbps). I would note that 5 seconds is very > long > >>>> in adaptation situations. > >>> > >>> Yes. > > > > In the proposed algorithm, the RTCP interval adds to the system response > > time. The response time governs the bandwidth increase rate so that the > step > > into over-use will have a limited delay build-up before it can be > detected > > and mitigated. Thus, a long RTCP interval results in a slow adaptation, > but > > it should still be stable. > > > > I wonder how would you guarantee that such a long RTCP interval > doesn't result in instability when estimating bandwidth? Typically, a > delay-based CC algorithm can be vulnerable when timer become > inacurate. I suspect the delayed RTCP feedback can calculate available > bandwidth correctly. Why not use per-packet based feedback (using > AVPF, for example) in order not to cause any harm with this kind of > situation? > I agree that more frequent feedback does improve the bandwidth estimation. No doubt about that. > I would think that a CC mechanism, at least, should be able to > calculate and suggest right/correct rate to the upper layer's codec so > that it could determine whether it actually increase/decrease encoding > rate or not, depending upon CC's suggested rate. > > > Kind regards, > Soo-Hyun > -- Henrik Lundin | WebRTC Software Eng | hlundin@google.com | +46 70 646 13 41
- [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