[ns] Reg. strange behaviour of throughput with changing interface queue length

[Karthik]

Hi people,
I have encountered a strange behavior with throughput on changing interface
queue length.

I am simulating a scenario where one node is an access point and the rest of
the wireless nodes  are sending it data via a TCP/FTP traffic source.

For higher number of nodes(10 - 40 nodes, for example) the throughput is
maximum when ifqlength is 5. throughput decreases a little when ifqlength is
changed to 10 and further reduces when it is 20.
After this, when I increase the ifq length further, the throughput profile(i
am plotting throughputVsnumber of nodes connected for each ifglength)
increases higher than it was for length=20. overall the total behavious is
sthg like this :
(Throughput)ifq=5 > (Th)ifq=10 > (Th)ifq=15 > (Th)ifq=20
(Th)ifq=20 < (Th)ifq=30 < (Th)ifq=40 < (Th)ifq=50

Did anyone encounter such behaviour or can offer any reasonable explanation
for this ?
I am not exactly sure how changing the interface queue length affects the
simulation. It would be great if anyone can throw some light.

Thank you !

Karthik