[e2e] Are Packet Trains / Packet Bursts a Problem in TCP?

Detlef Bosau 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 
asynchronous traffic.

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.


Detlef Bosau
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70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
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