Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)

Henrik Lundin <hlundin@google.com> Mon, 19 September 2011 08:02 UTC

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Date: Mon, 19 Sep 2011 10:04:47 +0200
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From: Henrik Lundin <hlundin@google.com>
To: Randell Jesup <randell-ietf@jesup.org>
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Subject: Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)
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Add me to the bof members list.

/Henrik L


On Mon, Sep 19, 2011 at 9:54 AM, Randell Jesup <randell-ietf@jesup.org>wrote;wrote:

>  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>wrote;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 Jesuprandell-ietf@jesup.org
>
>
> _______________________________________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb
>
>


-- 
Henrik Lundin | WebRTC Software Eng | hlundin@google.com | +46 70 646 13 41