[e2e] Why Buffering?

Detlef Bosau detlef.bosau at web.de
Sun Jun 21 14:13:03 PDT 2009

Christian Huitema wrote:
>>> Little's law (N = T lambda) holds in basically all scenarios.  It
>>> doesn't rely on stationarity.  It refers to long-run averages, which
>>> wash out all of the fluctuations.
>> I'm not quite sure here.
> The law certainly holds on all scenarios, but it is about averages. Remember the statistician who drowned in a pool of water that was 1 inch deep, in average?
> -- Christian Huitema

Of course. Actually, that shows that mathematical models may be a bit 
abstract ;-)

Actually, for the theorem to describe the reality with extremely long 
service times, the queue may grow extremely large ;-)

On the one hand, this shows that all these mathematical models tend to 
be an extremely abstract idealization. On the other hand, this is 
exactly one reason for queuing at all. As Jon pointed out, senders may 
be asynchronous, there is no synchronization between flows, particularly 
as we do not have packet schedulers in the Internet in most cases.
(There may be exceptions in labs ;-))

So, we need queues to achieve the "average".

However, as far as I know, there is some common sense to keep queues 
small. (And from what I've read, I did not read Len Kleinrock's text 
book myself but quotations from there, that's one of the lessons from 
Kleinrock's book. It's simply not feasible to run a system "far beyond 
the knee", IIRC this can even drastically decrease a system's throughput.)

Detlef Bosau		Galileistraße 30	70565 Stuttgart
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