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场景比较简单，主要是为了观察排队和丢包情况！ 脚本的拓扑结构： 通过利用NAM演示功能，可以明显看到TCP和UDP机制的区别： 三次握手、ACK消息、慢启动等！ 实例3： （以下的代码，在 入门实例1 中已进行了详细的注释）
- # 场景描述：
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# 主要用于观察数据包在节点Agent上的排队和丢包情况
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# 有线场景，四个节点，FTT+TCP用蓝色表示, CBR+UDP用红色表示
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set ns [new Simulator]
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#设置颜色
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$ns color 1 Blue
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$ns color 2 Red
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set tracefd [open out.tr w]
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$ns trace-all $tracefd
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set namtracefd [open out.nam w]
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$ns namtrace-all $namtracefd
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proc finish {} {
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global ns tracefd namtracefd
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$ns flush-trace
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close $tracefd
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close $namtracefd
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exec nam out.nam &
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exit 0
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}
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set n0 [$ns node]
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set n1 [$ns node]
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set n2 [$ns node]
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set n3 [$ns node]
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$ns duplex-link $n0 $n2 2Mb 10ms DropTail
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$ns duplex-link $n1 $n2 2Mb 10ms DropTail
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$ns duplex-link $n2 $n3 1.7Mb 10ms DropTail
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$ns queue-limit $n2 $n3 10
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-
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#用于设置NAM显示时，各节点的相对位置
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$ns duplex-link-op $n0 $n2 orient right-down
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$ns duplex-link-op $n1 $n2 orient right-up
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$ns duplex-link-op $n2 $n3 orient right
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$ns duplex-link-op $n2 $n3 queuePos 0.5
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set tcp [new Agent/TCP]
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$tcp set class_ 2
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$ns attach-agent $n0 $tcp
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set sink [new Agent/TCPSink]
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$ns attach-agent $n3 $sink
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$ns connect $tcp $sink
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$tcp set fid_ 1
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set ftp [new Application/FTP]
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$ftp attach-agent $tcp
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$ftp set type_ FTP
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set udp [new Agent/UDP]
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$ns attach-agent $n1 $udp
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set null [new Agent/Null]
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$ns attach-agent $n3 $null
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$ns connect $udp $null
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$udp set fid_ 2
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set cbr [new Application/Traffic/CBR]
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$cbr attach-agent $udp
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$cbr set type_ CBR
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$cbr set packet_size_ 1000
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$cbr set rate_ 1mb
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$cbr set random_ false
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$ns at 0.5 "$cbr start"
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$ns at 1.0 "$ftp start"
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$ns at 4.0 "$ftp stop"
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$ns at 4.5 "$cbr stop"
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#一下这一行可有可无！
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$ns at 4.5 "$ns detach-agent $n0 $tcp ; $ns detach-agent $n3 $sink"
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$ns at 5.0 "finish"
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#会在命令窗口中输出， 因为默认的stdout是命令窗口啊！
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puts "CBR packet size=[$cbr set packet_size_]"
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puts "CBR interval=[$cbr set interval_]"
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$ns run
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发表于 2011-12-22 08:53
