Packet Transmission on LAN

set ns [new Simulator]
set namfile [open lab3.tr w]
$ns namtrace-all $namfile
set namfile [open lab3.nam w]
Agent/TCP set packetSize_ 1460
set n0[$ns node]
set n1[$ns node]
set n2[$ns node]
set n3[$ns node]
set n4[$ns node]
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
$ns duplex-link $n1 $n2 1Mb 10ms DropTail
$ns make-lan "$n2 $n3 $n4" 100Mb 1ms LL Queue/DropTail Mac/802_3 Channel Phy/WiredPhy
set errmodel [new ErrorModel]
$errmodel set rate_ 0.2
$errmodel ranvar [new RandomVariable/Uniform]
$errmodel drop-target [new Agent/NULL]
$ns lossmodel $errmodel $n1 $n2
set tcp [new Agent/TCP]
$ns attach-agent $n0 $tcp
set sink [new Agent/TCPSink]
$ns attach-agent $n4 $sink
$ns connect $tcp $sink
set ftp [new Application/FTP]
$ftp attach-agent $tcp
set filesize [expr 4*1024*1024]
$ns at 0.0 "$ftp send $filesize"
proc finish {} {
global ns namfile tracefile
$ns flush-trace
close $namfile
close $tracefile
set awkCode {
BEGIN{}
{
if($1=="d"){
count_packets++;
print $2, count_packets >> "lab3.data"
}
}
END{}
}
exec awk $awkCode lab3.tr
exec xgraph -bb -tk -x Time -y Dropped_Packets lab3.data -bg white &
exit 0
}
$ns at 100.0 "finish"
$ns run