Re: [ns-users] Modeling ns TCP

[Yuri Pryadkin <yuri@who.isi.edu>]

I think s/b is the transmission delay and d is the propagation delay.
There is no 'processing' delay, so it seems you've got everything
covered.

 -Yuri

rik@scs.leeds.ac.uk writes:

> Despite the fact that I'm not being much of a mathematician, I really
> have to model TCP performance in ns (2.1b5) for a paper I'm working on.
> What I would like to do is predict the transmission window size at a
> given time. 
> 
> My results match the ns packet timestamp output up to a certain point
> in the simulation but then start to become less accurate. I have read
> through the documentation regarding link delays etc. and have the s/b+d
> (pkt size/bandwidth + delay) components. However, there appears to be a
> queueing or propagation delay which I'm not taking into account at the
> sender.
> 
> I'd really appreciate it if anyone could point me to the missing
> component(s). I currently have 1 RTT in ns as simply:
> 
>    transmission delay of PKT = #nodes_out*(s/b+d)
>  + transmission delay of ACK = #nodes_return*(s/b+d)
				 ^^^^^^^
you mean #of links (of same bw and delay), right?
		
> 
> (nodes_out == nodes_return) 
> 
> There does, however, seem to be an additional delay somewhere to do
> with the propagation of new packets from Tx. Any further information
> greatly appreciated.