[Codel] Regarding BDP, window size and queue-size for codel in ns2

[Jonathan Morton]

I recommended earlier to run Codel experiments with a very large buffer,
since Codel will keep it under control. For experimental rigour, you should
also run experiments involving other queue modes with the same buffer size,
and observe how well or badly each mode controls it.

As for receive window size, you should make that large enough that you will
notice the resulting delay easily. Modern operating systems will happily
use receive windows of several megabytes in default configurations; this
results in impressive delays at relatively low bandwidths. I've seen 45
seconds at 512Kbps.

You might also try setting up multiple simulated hosts with different
receive window sizes - including some sensibly small ones, such as the
65535 bytes which is the limit for TCP stacks without window scaling - and
see how they compete on the same congested link. This might give you some
insight into why such large windows seem desirable to those unaware of AQM,
and why they become mostly irrelevant when good AQM is introduced.

- Jonathan Morton
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