[e2e] Why Buffering?
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
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.)
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