set ns [new Simulator]
set node_(0) [$ns node]
set node_(1) [$ns node]
# Defining a transport agent for sending
set tcp [new Agent/TCP]
# Attaching transport agent to sender node
$ns attach-agent $node_(0) $tcp
# Defining a transport agent for receiving
set sink [new Agent/TCPSink]
# Attaching transport agent to receiver node
$ns attach-agent $node_(1) $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"
where,
ns → Simulator instance
TCP → Transmission Control Protocol
FTP → File Transfer Protocol