Re: question about token bucket filter

[Lee Breslau <breslau@research.att.com>]

The reason this isn't doing what you want is because the TBF you
created at n1 does not receive the packets generated at n0.
The TBF at n1 sits between the new agent, aa, and node n1.  Any
packets sourced by aa will pass through the TBF.  However, the
packets sourced by agent 'a' are forwarded from n0 to n1.  They
pass through the node object, n1, and are forwarded to n2.  They
do not reach the TBF.

Accomplishing what you want would require inserting the TBF into
the node object (instead of merely inserting the TBF between an agent
and its attached node).  This is certainly feasible, but I don't
think there are any functions currently in ns to do this (but I
may be wrong on that account).

Lee


> 
> Hi,
> 
>  In the token bucket example /tcl/ex/test-tbf.tcl, the tbf is used as:
> 
> set exp1 [new Application/Traffic/Exponential]
> set a [new Agent/UDP]
> $exp1 attach-agent $a
> set tbf [new TBF]
> $ns attach-tbf-agent $n0 $a $tbf
> 
> Topology: n0----------n2
> 
> i.e., The node 0 perform both traffic generation and tbf.
> 
> Right now, I wish to sperate them into node0 and node1, where
> node0 perform traffic generate and node1 perform tbf.
> 
> Topology n0----n1-------n2
> 
> set exp1 [new Application/Traffic/Exponential]
> set a [new Agent/UDP]
> $exp1 attach-agent $a
> $ns attach-agent $n0 $a
> set aa [new Agent/UDP]
> set tbf [new TBF]
> $ns attach-tbf-agent $n1 $aa $tbf
> 
> With this way, the traffic shape is the same before n1 and after n1.
> It seems that tbf applied in n1 is "transparent" to the traffic.
> 
> Your help is very appreciated.
> 
> 
> Po-Yuen Cheng