Otcl for NS2 (Acknowledgement Programe )

set  ns [new Simulator]
set  n1 [$ns node]
set  n2 [$ns node]

#Open the nam trace file
set nf [open out.nam w]
$ns namtrace-all $nf

#Define a 'finish' procedure
proc finish {} {
        global ns nf
        $ns flush-trace
    #Close the trace file
        close $nf
    #Execute nam on the trace file
        exec nam out.nam &
        exit 0
}
$ns duplex-link $n1 $n2 5Mb 2ms DropTail


 #=== TCP connection setup starts here ===
set tcp [new Agent/TCP]
set sink [new Agent/TCPSink]
set ftp [new Application/FTP]
$ns attach-agent $n1 $tcp
$ns attach-agent $n2 $sink
$ftp attach-agent $tcp
$ns connect $tcp $sink
$ns at 0.0 "$ftp start"


$ns at 5.0 "finish"

#Run the simulation
$ns run