实现4节点星型网络场景中网络带宽的测量,给出模拟过程中带宽变化情况的曲线图(Xgraph绘制)!
星型拓扑结构,但是其中有两点我还没搞清:
1.set traffic [new Application/Traffic/Exponential]
该traffic应用被连接到UDP连接之上,但是具体是什么样的数据流呢?
2.set sink0 [new Agent/LossMonitor]
这种UDPSink,从字面上理解可以监听丢包,
但是实际只用到了节点采样时刻接受到的数据包字节数,即:set bw0 [$sink0 set bytes_]
以后搞懂了,再做具体说明吧!
学习的知识点:
如何通过统一方式设置同一类型的连接(代码重用:简洁地生成节点,大规模场景就是采用这种生成方式)!
如何写采样过程record, 通过调用 $ns at [expr $now+$time] "record" 实现间隔采用(每隔 $time 后进行一次采样), 深刻理解NS2模拟的事件调度机制(事件队列:FIFO)!
如何利用Xgraph进行曲线绘制,以及Xgraph源文件格式!
#场景描述: #有线新星结构, 四节点, 三条UDP连接,中心节点公用 #测量模拟过程中,各条UDP连接的带宽!
#以下是一些基本设置,在看过NS系列--NS2入门实例1、2、3之后,阅读肯定没问题的啦! set ns [new Simulator] set tracefd [open trace.tr w] $ns trace-all $tracefd set namtracefd [open namtrace.nam w] $ns namtrace-all $namtracefd
set f0 [open out0.tr w] set f1 [open out1.tr w] set f2 [open out2.tr w]
set n0 [$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 $n4 $n3 1Mb 100ms DropTail
#参数的意义: node sink size burst idle rate # node:数据流的发起节点 # sink:数据流对应的接收代理 # size、idle、rate:数据包大小、idle时间、发包速率
proc attach-expoo-traffic { node sink size burst idle rate } { #生成simulator实例对象,用于整个仿真过程 set ns [Simulator instance] #创建UDP代理,并与soure节点相关联 set source [new Agent/UDP] $ns attach-agent $node $source #Create an Expoo traffic agent and set its configuration parameters set 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 $sink return $traffic }
proc record {} { #注意:自己写采样过程时,把要用到的变量做声明很重要! global sink0 sink1 sink2 f0 f1 f2 #Get an instance of the simulator set ns [Simulator instance] #Set the time after which the procedure should be called again set time 0.5 #How many bytes have been received by the traffic sinks? set bw0 [$sink0 set bytes_] set bw1 [$sink1 set bytes_] set bw2 [$sink2 set bytes_] #Get the current time set now [$ns now] #Calculate the bandwidth (in MBit/s) and write it to the files puts $f0 "$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 #这点很重要,以重新采样时不受前一次的影响,与NS2实现机制有关,暂时可忽略! $sink0 set bytes_ 0 $sink1 set bytes_ 0 $sink2 set bytes_ 0 #Re-schedule the procedure $ns at [expr $now+$time] "record" } #LossMonitor的特点:? 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 #调用过程proc attach-expoo-traffic { node sink size burst idle rate } #可以很方便的设置同一类型的数据流 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]
proc finish {} { global f0 f1 f2 tracefd namtracefd close $f0 close $f1 close $f2 close $tracefd close $namtracefd exec nam namtrace.nam & #Call xgraph to display the results exec xgraph out0.tr out1.tr out2.tr -geometry 800x400 & exit 0 }
$ns at 0.0 "record" $ns at 10.0 "$source0 start" $ns at 10.0 "$source1 start" $ns at 10.0 "$source2 start" $ns at 50.0 "$source0 stop" $ns at 50.0 "$source1 stop" $ns at 50.0 "$source2 stop" $ns at 60.0 "finish" $ns run |
运行结果:(拓扑图比较简单,运行之后自己看哦!)
对结果的简单分析:
各条UDP链路的最大值,与预先设置的一致!
但是,其中的变化,我还不甚明了!
测量结果:
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