> On 4 Jun, 2016, at 23:04, Alan Jenkins <[email protected]> 
> wrote:
> 
> Am I right in thinking Steam uses a torrent download?

No; though it is a multi-stream system, it’s basically HTTP (with offset/range) 
plus some minor special sauce.  Several files can be fetched at once in 
parallel, and these separate connections are usually to different servers.

It differs from torrent swarms most fundamentally in that there is no 
uploading; all the content comes from official servers.  This also means that 
fewer connections are needed to fill a given download pipe (usually just one 
would do the trick).

We’re at a significant disadvantage because we typically have to apply our AQM 
*after* the bottleneck link in the downstream direction.  This means we have to 
somehow prevent senders from sending too many packets in order to avoid 
inducing delay within the ISP’s dumb buffers, rather than being able to buffer 
them smartly ourselves as a last resort.  We therefore rely on effective 
congestion control, with flow-isolation being primarily a means to target the 
signals more precisely.

Servers which defeat our primary method of doing so (by ignoring the copious 
signals saying “slow down please”) are ultimately unhelpful.  But at least they 
are still ack-clocked.

 - Jonathan Morton

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