一款用来进行网络模拟的软件

				# simple stop-ane-wait protocol								set ns [new Simulator]								set n0 [$ns node]				set n1 [$ns node]								$ns at 0.0 "$n0 label Sender"				$ns at 0.0 "$n1 label Receiver"								set nf [open test-ptp-1.nam w]				$ns namtrace-all $nf								$ns duplex-link $n0 $n1 0.2Mb 200ms DropTail				$ns duplex-link-op $n0 $n1 orient right								set tcp [new Agent/TCP]				$tcp set maxcwnd_ 1				$ns attach-agent $n0 $tcp								set sink [new Agent/TCPSink]				$ns attach-agent $n1 $sink				$ns connect $tcp $sink								set ftp [new Application/FTP]				$ftp attach-agent $tcp								### set operations				$ns at 0.01 "$ftp start"				$ns at 2.6 "$ftp stop"				$ns at 2.6 "finish"								### take snapshots				foreach i "0.0 0.3 0.6 0.9 1.2 1.3 1.4 \ 				1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5" {				$ns at $i "$ns snapshot"				}								### take snapshot operations				$ns at 1.25 "$ns re-rewind-nam"				$ns at 2.2 "$ns rewind-nam"				$ns at 2.55 "$ns terminate-nam"								### add annotations				$ns at 0.0 "$ns trace-annotate \"Simple Stop-and-Wait protocol\""				$ns at 0.01 "$ns trace-annotate \"FTP starts at 0.1\""				$ns at 2.49 "$ns trace-annotate \"FTP stops\""								proc finish {} {				        global ns nf				        $ns flush-trace				        close $nf				        exit 0				}								$ns run