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Date: Tue, 9 Jul 2013 10:56:36 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Jaume Barcelo <jaume.barcelo@upf.edu>
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Cc: bloat@lists.bufferbloat.net
Subject: Re: [Bloat] sweet tcp
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On Tue, 9 Jul 2013 19:38:40 +0200
Jaume Barcelo <jaume.barcelo@upf.edu> wrote:

> To be more specific, TCP would be at any time increasing or decreasing
> the congestion window. In other words, it will be moving in one
> direction (right or left) along the x axis of Fig. 1 of Getty's paper.
> Each RTT, the performance is measured in terms of delay and
> throughput. If there is a performance improvement, we keep moving in
> the same direction. If there is a performance loss, we change the
> direction.

TCP can not get a reliable measure of RTT. This is the whole reason
that delay based algorithms are not widely deployed and don't work
outside the lab. The issue is that other traffic perturbs RTT measurements
have a huge variance on a real network  (more noise than signal).