Re: Q: understanding classifiers

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

Urs Thuermann <thuerman@ibr.cs.tu-bs.de> writes:

> Trying to understand node, classifiers and link I looked at the object
> structure after setting up the following topologie:
> 
> 	set ns [new Simulator]
> 	set n0 [$ns node]
> 	set n1 [$ns node]
> 	$ns duplex-link $n0 $n1 10Mb 10ms DropTail
> 	set udp [new Agent/UDP]
> 	set null [new Agent/Null]
> 	$ns attach-agent $n0 $udp
> 	$ns attach-agent $n1 $null
> 	$ns connect $udp $null
> 
> The addresses of $udp and $null are what I expected:
> 
> 	% $udp set addr_
> 	0
> 	% $null set addr_
> 	256
> 
> I thought the classifier at node $n0 should have an entry in its
> slots_ array pointing to the link from $n0 to $n1 but
>
> 
> 
> 	% set c0 [$n0 set classifier_]
> 	_o12
> 	% $c0 dump
> 	classifier _o12
> 		0 offset
> 		8 shift
> 		127 mask
> 		1 slots
> 			slot 0: _o29

This is 'Node instvar classifier_'

> 	% _o29 dump
> 	classifier _o29
> 		0 offset
> 		0 shift
> 		255 mask
> 		1 slots
> 			slot 0: _o27
> 	% puts $udp
> 	_o27

And this is 'Node instvar dmux_' - port demuxer.

> 
> but surprinsingly the classifier at $n0 only has an entry pointing to
> another classifier _o29 which in turn only has one slot pointing back
> to $udp.
> 
> The classifier $c0 has shift_ == 8 and mask_ == 127, i.e. when sending
> a packet to
> 
> 	% $udp set dst_
> 	256
> 
> which is the correct address of $null, the classifier $c0 calculates
> slot number (256 >> 8) & 127 which results in 1.  However, $c0 has no
> entry in slot_[1].  In the C++ code there is a default_target_ in
> class Classifier.  Is this used here?  Can its value be accessed from
> Tcl somehow without changing the ns source?

Default routes will be computed and installed in the classifier when
the simulator is run (see Simulator instproc run).

> 
> 
> urs