[Bloat] Not all the world's a WAN

[Richard Scheffenegger]

Some do. i.e. l3 capable switches, broadcom scorpio (and later) can do ecn 
marking based on l2 buffer occupancy.

see the paper from stanford/microsoft about dctcp - ecn marking based on 
instantaneous buffer occupancy and proportional tcp reaction (rather than 
halving cwnd) per rtt...

rgds
----- Original Message ----- 
From: <BeckW at telekom.de>
To: <sgunderson at bigfoot.com>; <bloat at lists.bufferbloat.net>
Sent: Friday, August 19, 2011 4:59 PM
Subject: Re: [Bloat] Not all the world's a WAN


>> [...]so over short intervals the switch's aggregate incoming bandwidth 
>> (multiple 10GbE links from
>> servers) is larger than its outgoing bandwidth (single 10GbE link to 
>> client).
>
> Well, this kind of burstiness is the reason why we have buffers at all.
>
> Restricting the window size limits the TCP speed and keeps it this way 
> from overflowing the buffer outside of bursty periods.
>
> ECN marking helps TCP to distinguish between really available bandwidth 
> and 'fake' bandwidth that just fills up a buffer, at least if the feedback 
> loop is fast enough. Do ethernet switches support ECN marking?
>
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