Question about the traffic shaping

[Dong Mo]

Hi Dear Group,

I am now using some very simple traffic shaping as:

set link0 [$ns duplex-link $receiver $sender 150M 30ms DropTail]

However, if I test this link with iperf, it can only achieve throughput of 20+Mbps instead of 150Mbps...

Is there any solution to this problem?

Thank you

-Mo Dong

[Thanh Do]

I think the latency (30ms) would affect bandwidth,

you could try 0ms latency and see.

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[Dong Mo]

I tried it reaches to 100Mbps

I can use udp to reach 150Mbps. 

So I am wondering is it because of some limited buffer size in this setting that is dropping bursty TCP packets and it hinders TCP to reach to full rate?

2013/4/30 Thanh Do <tha...@cs.wisc.edu>

[Kirk Webb]

Try opening up the TCP window in iperf with the "-w" switch.
Otherwise, when you introduce delay, the TCP bandwidth may dip due to
flow control (delay-bandwidth product).

[Robert Ricci]

Or, to put it another way: what Emulab tries to do is give you the
*capacity* for bandwidth that you asked for in your NS file; this does
not automatically mean that your application (iperf in this case) is
tuned to reach that bandwidth. The most common form that this takes is
needing to adjust to the bandwidth-delay project, which is what Kirk's
mail addresses.