NS2 simulation for UDP packets in a network

set ns [new Simulator]

set nf [open out.nam w]
$ns namtrace-all $nf

set nt [open out.tr w]
$ns trace-all $nt

proc finish {} {
        global ns nf nt
        $ns flush-trace
        close $nf
        close $nt
        exec nam out.nam &
        exit 0
        }

set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]

$ns duplex-link $n0 $n1 1Mb 10ms DropTail
$ns duplex-link $n1 $n2 1Mb 10ms DropTail
$ns duplex-link $n0 $n2 1Mb 10ms DropTail

$ns duplex-link-op $n0 $n1 orient right-up
$ns duplex-link-op $n0 $n2 orient right

set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0

set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 500
$cbr0 set interval_ 0.005
$cbr0 attach-agent $udp0

set null0 [new Agent/Null]
$ns attach-agent $n2 $null0

$ns connect $udp0 $null0

$ns at 0.5 "$cbr0 start"
$ns at 4.5 "$cbr0 stop"

$ns run