Re: [ns] some problem about variable link delay realizing

["Nikolaos Katsarakis Austauschstud. (M. Schweigel)" <katsarak@ifn.et.tu-dresden.de>]

Sorry, the previous message was incomplete.

You have to make a function like record() and use the [$dy value]
command

e.g.

set dy [new RandomVariable/Uniform]
$dy set min_10
$dy set max_20
$ns simplex-link node0 node1 9600bps dy DropTail
set interval 0.01

proc record {interval} {
global dy node0 node1
	#Get an instance of the simulator
	set ns [Simulator instance]
	#Get a value of the random variable
	set new_delay [$dy value]
	#Change link delay
	$ns delay $node0 $node1 $new_delay duplex
	#Set the time after which the procedure should be called again
	set time $interval
	$ns at [expr $now_str+$interval] "record $interval"
}

This command will change the delay of the link every $interval seconds.
But it will slow down the simulations, because in order to change the
delay for each packet, the interval should be very small. There should
be a way to issue the command for every packet to be sent, using the
evalf command, but I don't know which .c file is responsible for
dequeuing and sending the data. Any suggestions? I have done it in tcl
for every file to be sent. When I want to send a file of x bytes,
instead of calling $tcp send x, I call $tcp mysend x, and the mysend
command changes the delay before sending like below:

Agent/TCP instproc mysend {size} {
	#change delay
	$self changedel
	$self send $size
}

Agent/TCP instproc change_del {} {
	#change delay of link from agent node to node0
	global ns dy node0
	#get node where agent resides
	set mynode [$self set node_]
	set new_delay [$dy value]
	$ns delay $node0 $mynode $new_delay duplex
}

luorui999 wrote:

>
>
>  Thanks for your good advice!
>
>  More precisely, my question is this, for  ns-2 command,
>
> set dy [new RandomVariable/Uniform]
>
> $dy set min_10
>
> $dy set max_20
>
> $ns simplex-link node0 node1 9600bps dy DropTail
>
> may I use these commands make the link delay between node0 and node1
> vary as a random variable according to uniform distribution in the
> simulation?
>
>      ----- Original Message -----
>
>
>      You can use the delay command to change the delay of a link.
>
>      $ns delay $node1 $node2 $new_delay duplex
>
>      However if you do that, the nam will not visualise it very
>      well (at
>      least mine, nam 1.0a9)
>
>      luorui999 wrote:
>
>      >
>      >
>      > hi,
>      >
>      > I am a new user of ns-2, I am just simulating a system
>      whose link
>      > delay is variable, that is,the time that packet cost on
>      the link is
>      > not constant, but is random variable, the continus two
>      packet on the
>      > link may have different link delay, who can tell me how to
>      realize it
>      > with ns-2?
>      >
>      > thanks very much!
>      >
>      -----------------------------------------------------------------------
>
>      > 24P!J1Kx6(KQ:|PBNEVPPD#,HHARW#:X11>)Ij0BT2Bz3I9&#!
>
>
>
>
>
> -----------------------------------------------------------------------
>