set ns [new Simulator]

set totalTime 20.0
set bottleQueueSize 17

#Define a 'finish' procedure
proc finish {} {
    global ns f 
    close $f
    exec xgraph out.tr -geometry 400x800 &
    exit 0
}

set host0 [$ns node]
set host1 [$ns node]
set host2 [$ns node]

$ns simplex-link $host0 $host1 1MB 0.01s DropTail
$ns simplex-link $host1 $host2 100kB 0.01s DropTail
$ns simplex-link $host2 $host0 1MB 0.01s DropTail

set bottleQ [[$ns link $host1 $host2] queue]
$bottleQ set limit_ $bottleQueueSize

set tcp [new Agent/TCP]
$tcp set packetSize_ 1000

set sink [new Agent/TCPSink]

$ns attach-agent $host0 $tcp
$ns attach-agent $host2 $sink

$ns connect $sink $tcp

set ftp [new Application/FTP]
$ftp attach-agent $tcp

set f [open out.tr w]

#Define a procedure that periodically records the congestion window size 
proc record {} {
    global f tcp ns totalTime
    set time [expr $totalTime/600.0]
    #set w to the congestion window size
    set w [$tcp set cwnd_]
    set now [$ns now]
    puts $f "$now $w"
    #Re-schedule the procedure
    $ns at [expr $now+$time] "record"
}

$ns at 0.0 "$ftp start"
$ns at 0.0 "record"
$ns at $totalTime "$ftp stop"
$ns at [expr $totalTime + 1.5] "finish"
$ns run