[e2e] Are Packet Trains / Packet Bursts a Problem in TCP?
detlef.bosau at web.de
Wed Sep 27 15:34:49 PDT 2006
David P. Reed wrote:
> Fred - reasona ble response, but I take issue with your statement that
> the goal is "full use ot the bottleneck without overburdening it".
> Little's Lemma would suggest that idea is unreasonable.
> In the OS community, we used to have a rule of thumb that operating
> above 50% of the service rate of almost any multiplexed resource is
> problematic, unless you have a very precise and completely predictable
> and constant load. And Odlyzko has shown that enterprises are happy
> to run at about 10% capacity in return for lowering other, much more
> significant costs (such as jitter, latency, unreliability).
> Perhaps the real message is that obsession with the fantasy that such
> a goal is achievable has led to incredibly silly research efforts like
> the I2 hotrod compettions.
If I got this right, my spontaneous question is, whether we focus on the
right target: Is burstiness our problem? Or is burstiness a conseuqence
of flooding a network path which it cannot convey anyway, exactly
_because_ we cannot achieve a "perfect TDM behviour"?
Wouldn´t this suggest (and I had a short glance at Fred´s answer and
perhaps he might contradict here) that we intendedly drop the goal of
achieving a full load in favour of a "load dependend ECN" mechanism,
i.e. when the load of a link exceeds a certain limit, say 50 % of the
bandwidth, any passing packets are stamped with a forward congestion
notification. Thus, we would keep the throughput on a limit we cannot
exceed anyway, but limit the incomming traffic that way that queues can
fullfill their purpose, i.e. interleave the flows and buffer out
Perhaps the idea is silly, perhaps its from stoneage and published
dozens of times, but its just a spontaneous thought which comes to my mind.
Mail: detlef.bosau at web.de
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