[Bloat] Steam's distribution service - exceeding inbound policiers and bufferbloat

[cloneman]

thanks for the info. This is a possibility, as I have 5ms latency to their
servers with 50mbit of bandwidth.

On May 21, 2017 8:49 AM, "Benjamin Cronce" <bcronce at gmail.com> wrote:

> All current TCP implementations have a minimum window size of two
> segments. If you have 20 open connections, then the minimum bandwidth TCP
> will attempt to consume is (2 segments * 20 connection)/latency. If you
> have very low latency relative to your bandwidth, the sender will not
> respond to congestion.
>
> On Thu, Apr 6, 2017 at 9:47 PM, cloneman <cloneman at gmail.com> wrote:
>
>> Hi,
>>
>> Appologies in advance if this is the wrong place to ask, I haven't been
>> able to locate an official discussion board.
>>
>> I'm looking for any comments on Steam's game distribution download system
>> - specifically how it defeats any bufferbloat mitigation system I've used.
>>
>> It seems to push past inbound policers, exceeding them by about 40%. That
>> is to say, if you police steam traffic to half of your line rate, enough
>> capacity will remain to avoid packet loss, latency, jitter etc. Obviously
>> this is too much bandwidth to reserve.
>>
>> Without any inbound control, you can expect very heavy packet loss and
>> jitter. With fq_codel or sfq and taking the usual recommended 15% off the
>> table, you get improved, but still unacceptable performance in your small
>> flows / ping etc.
>>
>> The behavior can be observed by downloading any free game on their
>> platform. I'm trying to figure out how they've accomplished this and how to
>> mitigate this behavior. It operates with 20 http connections
>> simultaneously, which is normally not an issue (multiple web downloads
>>  perform well under fq_codel)
>>
>> Note: in my testing cable and vdsl below 100mbit were vulnerable to this
>> behavior, while fiber was immune.
>>
>> Basically there are edge cases on the internet that like to push too many
>> bytes down a line that is dropping or delaying packets. I would like to see
>> more discussion on this issue.
>>
>> I haven't tried tweaking any of the parameters / latency targets in
>> fq_codel.
>>
>>
>> _______________________________________________
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>> Bloat at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/bloat
>>
>>
>
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