# Defining a transport agent for sending
set tcp [new Agent/TCP]
# Attaching transport agent to sender node
$ns attach-agent $sender $tcp
# Defining a transport agent for receiving
set sink [new Agent/TCPSink]
# Attaching transport agent to receiver node
$ns attach-agent $receiver $sink
#Connecting sending and receiving transport agents
$ns connect $tcp $sink
#Defining Application instance
set ftp [new Application/FTP]
# Attaching transport agent to application agent
$ftp attach-agent $tcp
# data packet generation starting time
$ns at 1.0 "$ftp start"
# data packet generation ending time
$ns at 6.0 "$ftp stop"
set cwnd [$tcp set cwnd_]
puts “Congestion Window Size = $cwnd”