Subject: Re: [Ice] Example of data transmission without congestion control

From: 🔓Dan Wing <[email-masked]>
Date: Wed, 3 Aug 2016 08:58:22 -0700

I don't know the context to your post, as I wasn't at Berlin ICE meeting.  So perhaps I am speaking out of context.  I'll bring up my point anyway.

(Effectively) all Internet access around the world is asymmetric bandwidth.  Two examples:  Comcast's advertised 150Mbps speed provides 20Mbps upstream, and ADSL advertised 6Mbps downstream speed typically provides about 600kbps upstream.  Are we comfortable flooding these smaller upstream links?  I feel comfortable at 20Mbps, but I feel less comfortable at 600kbps.  This is one reason ICE originally paced itself to not exceed the bandwidth of the SDP-advertised codec.

-d

On 21-Jul-2016 03:01 am, Martin Thomson <[email-masked]> wrote:
> 
> I forgot to add my sources:
> 
> This is highly relevant:
> https://insouciant.org/tech/network-congestion-and-web-browsing/
> 
> On 21 July 2016 at 11:57, Martin Thomson <[email-masked]> wrote:
>> In HTTP/1.1, browsers will open 6 connections to the same site.  Many
>> sites are now deploying TCP stacks with an initial congestion window
>> of 10.  If we assume an MSS of 1400, that means that some sites will
>> send 1400*10*6 bytes without congestion control.  Most likely, these
>> 840 kilobits will arrive in less than a second.  840kbps is more than
>> we are asking for with ICE.
>> 
>> In practice, this can be worse because with TLS you have a round trip
>> over which the window is increased, though it's probably just one or
>> two packets more.
>> 
>> We also have examples of sites that use domain sharding to increase
>> the connection limit to as much as 30.  That does horrific things to
>> the network, so I don't think that we should use that as an argument.
>> I tend to think that 6*IW10 is also pretty dicey, but it's an example
>> of something that is widely deployed.
> 
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