Re: [ns] Flowmon

[Ratul Mahajan <ratul@cs.washington.edu>]

>  I tried to find an answer to my question from the mail archive but I
> cannot get a clear answer.
>  I have two distinct flows which I number explicitly flow 1 and flow 2
> respectively:
> $cbr set fid_ 1
> $ftp set fid_ 2
>  I want to collect statistics for a flow at each node it crosses. I use
> the following code for one of them:
> set fmon01 [$ns makeflowmon Fid]
> $ns attach-fmon [$ns link $n0 $n1] $fmon01
>  Unfortunately this doesn't work.What I get is aggregate statistics.
>  How do I specify the flow id I am interested to monitor?

Look at the example scripts using the flowmonitor. There are some in
~ns/tcl/test/ and ~ns/tcl/ex/ (~ns/tcl/rtmechanisms/ also has it).
In short, you have to call a dump function on the flowmonitor which would
dump the information for all the flows it has seen.

>  Flowmon works at a link level? That is to say monitors packets when they
> flow through links?Is there a way to check the statistics of a certain
> flow at a particular node instead?

One way is to instantiate a flowmon for every link connected to the
node. 
Another hack is to break a single logcal node into two physical nodes with
unidirectional links.

Initial topology -

	1----0---2


All the links are bidirectional and you are interested in node 0. Convert
this to
	______________
	|	      |
	v   	      |
	1---->0'---->0''----->2
	      ^		      |
	      |_______________|

The dircetion of the links are shown in the figure above. And you'll
monitor link 0'->0''		


	- Ratul
	
> --
> "Provability is a weaker notion than truth, no matter what axiom system is
> involved ... "
> 
> Kurt Godel (1906-1978)
> 
>  
> 
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