Re: [ns] tcp window_

[Brian Lee Bowers <bowersb@lanl.gov>]

On Monday 06 August 2001 11:01, M S wrote:
> hi
> could someone tell me as to how the Agent/TCP window_ value
> has to be set? ns-default.tcl sets window_ as 20.
>
> Take the following example:
>
>     n1-------------->n2-------------->n3
>    (src)    15Mb           15Mb     (dest)
>              0.01s          0.01s
>
> FTP application is attached to n1.
> For this topology what all variables(window_ or windowinit or
> tcpTick etc) should i play around with in order to achieve
> maximum throughput.

Your bottleneck link has a bandwidth of 15Mbps.  RTT is 40ms.
	40ms/RTT * 15Mbps
==>	600Kb/RTT

I assume that you are using the ns packet size of 1000 bytes, which 
is 8000b.
	600Kb/RTT / 8Kb/pkt
==>	75pkt/RTT

You should set your window_ variable to be not less than 75 if you 
want to keep the pipe full (assuming only a single flow as you've 
shown).  You can go larger than 75, but the extra packets will be 
queued at n2.  If you make window_ larger than 75 + queue size of n2, 
you will eventually drop packets.

If you decide to use 1500 byte packets, you will have to reduce your 
window_ variable to get perfrect throughput.  The math isn't hard, so 
I leave it to you.

-- 
Brian Lee Bowers	|	RADIANT Team (Summer Intern)
bowersb@lanl.gov	|	Los Alamos National Laboratory