經(jīng)過前面學(xué)習(xí)代碼的編寫，這一部分，我們要學(xué)會(huì)如何進(jìn)行分析，一個(gè)很直觀的方式就是將結(jié)果圖形化表示出來。

ns-allinone包的一部分是“xgraph”，一個(gè)繪圖程序，可用于創(chuàng)建模擬結(jié)果的圖形表示。 在本節(jié)中，將向您展示如何在Tcl腳本中創(chuàng)建可用作xgraph數(shù)據(jù)集的輸出文件的簡單方法。 在途中，還將向您展示如何使用流量生成器。（這里介紹的技術(shù)是創(chuàng)建適合xgraph的輸出文件的許多可能方式之一）

1、創(chuàng)建拓?fù)鋱D

首先，我們需要?jiǎng)?chuàng)建一個(gè)如下圖的拓?fù)鋱D。

代碼如下所示：

set n0 [$ns node] set n1 [$ns node] set n2 [$ns node] set n3 [$ns node] set n4 [$ns node]$ns duplex-link $n0 $n3 1Mb 100ms DropTail $ns duplex-link $n1 $n3 1Mb 100ms DropTail $ns duplex-link $n2 $n3 1Mb 100ms DropTail $ns duplex-link $n3 $n4 1Mb 100ms DropTail我們將流量源附加到節(jié)點(diǎn)n0，n1和n2，但是首先我們編寫一個(gè)程序，將流量源附加到節(jié)點(diǎn)n0，n1和n2
proc attach-expoo-traffic { node sink size burst idle rate } {#Get an instance of the simulatorset ns [Simulator instance]#Create a UDP agent and attach it to the nodeset source [new Agent/UDP]$ns attach-agent $node $source#Create an Expoo traffic agent and set its configuration parametersset traffic [new Application/Traffic/Exponential]$traffic set packetSize_ $size$traffic set burst_time_ $burst$traffic set idle_time_ $idle$traffic set rate_ $rate# Attach traffic source to the traffic generator$traffic attach-agent $source#Connect the source and the sink$ns connect $source $sinkreturn $traffic }它有六個(gè)參數(shù)：一個(gè)節(jié)點(diǎn)，一個(gè)先前創(chuàng)建的流量信宿，流量源的數(shù)據(jù)包大小，突發(fā)和空閑時(shí)間（指數(shù)分布）和峰值速率。
首先，該過程創(chuàng)建流量源并將其附加到節(jié)點(diǎn)，然后創(chuàng)建一個(gè)Traffic / Expoo對(duì)象，設(shè)置其配置參數(shù)并將其附加到流量源，最后連接源和宿。 最后，該過程返回流量來源的句柄。 這個(gè)過程是一個(gè)很好的例子，可以處理如何將諸如將流量源附加到多個(gè)節(jié)點(diǎn)的任務(wù)。 現(xiàn)在我們使用這個(gè)過程將具有不同峰值速率的流量源連接到n0，n1和n2，并將它們連接到n4上的三個(gè)流量接收器，這些流量源必須首先創(chuàng)建：

set sink0 [new Agent/LossMonitor] set sink1 [new Agent/LossMonitor] set sink2 [new Agent/LossMonitor] $ns attach-agent $n4 $sink0 $ns attach-agent $n4 $sink1 $ns attach-agent $n4 $sink2set source0 [attach-expoo-traffic $n0 $sink0 200 2s 1s 100k] set source1 [attach-expoo-traffic $n1 $sink1 200 2s 1s 200k] set source2 [attach-expoo-traffic $n2 $sink2 200 2s 1s 300k]在這個(gè)例子中，我們使用Agent / LossMonitor對(duì)象作為流量接收器，因?yàn)樗鼈兇鎯?chǔ)接收的字節(jié)數(shù)，我們可以使用這個(gè)來計(jì)算帶寬。
現(xiàn)在我們可以寫出實(shí)際將數(shù)據(jù)寫入輸出文件的程序。

proc record {} {global sink0 sink1 sink2 f0 f1 f2#Get an instance of the simulatorset ns [Simulator instance]#Set the time after which the procedure should be called againset time 0.5#How many bytes have been received by the traffic sinks?set bw0 [$sink0 set bytes_]set bw1 [$sink1 set bytes_]set bw2 [$sink2 set bytes_]#Get the current timeset now [$ns now]#Calculate the bandwidth (in MBit/s) and write it to the filesputs $f0 "$now [expr $bw0/$time*8/1000000]"puts $f1 "$now [expr $bw1/$time*8/1000000]"puts $f2 "$now [expr $bw2/$time*8/1000000]"#Reset the bytes_ values on the traffic sinks$sink0 set bytes_ 0$sink1 set bytes_ 0$sink2 set bytes_ 0#Re-schedule the procedure$ns at [expr $now+$time] "record" }此程序讀取從三個(gè)流量接收器接收的字節(jié)數(shù)。 然后，它計(jì)算帶寬（以MBit / s為單位），并將其與當(dāng)前時(shí)間一起寫入三個(gè)輸出文件，然后重置流量匯點(diǎn)上的bytes_值。

2、運(yùn)行模擬

首先，調(diào)用“record”過程，然后每0.5秒定期重新安排一次。 然后三個(gè)流量來源在10秒鐘開始，并在50秒鐘停止。 在60秒鐘后，調(diào)用“finish”過程。完整的腳本代碼如下：

#Create a simulator object set ns [new Simulator]#Open the output files set f0 [open out0.tr w] set f1 [open out1.tr w] set f2 [open out2.tr w]#Create 5 nodes set n0 [$ns node] set n1 [$ns node] set n2 [$ns node] set n3 [$ns node] set n4 [$ns node]#Connect the nodes $ns duplex-link $n0 $n3 1Mb 100ms DropTail $ns duplex-link $n1 $n3 1Mb 100ms DropTail $ns duplex-link $n2 $n3 1Mb 100ms DropTail $ns duplex-link $n3 $n4 1Mb 100ms DropTail#Define a 'finish' procedure proc finish {} {global f0 f1 f2#Close the output filesclose $f0close $f1close $f2#Call xgraph to display the resultsexec xgraph out0.tr out1.tr out2.tr -geometry 800x400 &exit 0 }#Define a procedure that attaches a UDP agent to a previously created node #'node' and attaches an Expoo traffic generator to the agent with the #characteristic values 'size' for packet size 'burst' for burst time, #'idle' for idle time and 'rate' for burst peak rate. The procedure connects #the source with the previously defined traffic sink 'sink' and returns the #source object. proc attach-expoo-traffic { node sink size burst idle rate } {#Get an instance of the simulatorset ns [Simulator instance]#Create a UDP agent and attach it to the nodeset source [new Agent/UDP]$ns attach-agent $node $source#Create an Expoo traffic agent and set its configuration parametersset traffic [new Application/Traffic/Exponential]$traffic set packetSize_ $size$traffic set burst_time_ $burst$traffic set idle_time_ $idle$traffic set rate_ $rate# Attach traffic source to the traffic generator$traffic attach-agent $source#Connect the source and the sink$ns connect $source $sinkreturn $traffic }#Define a procedure which periodically records the bandwidth received by the #three traffic sinks sink0/1/2 and writes it to the three files f0/1/2. proc record {} {global sink0 sink1 sink2 f0 f1 f2#Get an instance of the simulatorset ns [Simulator instance]#Set the time after which the procedure should be called againset time 0.5#How many bytes have been received by the traffic sinks?set bw0 [$sink0 set bytes_]set bw1 [$sink1 set bytes_]set bw2 [$sink2 set bytes_]#Get the current timeset now [$ns now]#Calculate the bandwidth (in MBit/s) and write it to the filesputs $f0 "$now [expr $bw0/$time*8/1000000]"puts $f1 "$now [expr $bw1/$time*8/1000000]"puts $f2 "$now [expr $bw2/$time*8/1000000]"#Reset the bytes_ values on the traffic sinks$sink0 set bytes_ 0$sink1 set bytes_ 0$sink2 set bytes_ 0#Re-schedule the procedure$ns at [expr $now+$time] "record" }#Create three traffic sinks and attach them to the node n4 set sink0 [new Agent/LossMonitor] set sink1 [new Agent/LossMonitor] set sink2 [new Agent/LossMonitor] $ns attach-agent $n4 $sink0 $ns attach-agent $n4 $sink1 $ns attach-agent $n4 $sink2#Create three traffic sources set source0 [attach-expoo-traffic $n0 $sink0 200 2s 1s 100k] set source1 [attach-expoo-traffic $n1 $sink1 200 2s 1s 200k] set source2 [attach-expoo-traffic $n2 $sink2 200 2s 1s 300k]#Start logging the received bandwidth $ns at 0.0 "record" #Start the traffic sources $ns at 10.0 "$source0 start" $ns at 10.0 "$source1 start" $ns at 10.0 "$source2 start" #Stop the traffic sources $ns at 50.0 "$source0 stop" $ns at 50.0 "$source1 stop" $ns at 50.0 "$source2 stop" #Call the finish procedure after 60 seconds simulation time $ns at 60.0 "finish"#Run the simulation $ns run

鏈接：http://www.isi.edu/nsnam/ns/tutorial/

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