运行NS2代码时出现LanRouter::debug_警告与ftp2变量不存在报错

1 致命错误：can't read " ftp2: no such variable" #

原因 #

你在代码中直接调用了$ ftp2的启动、停止指令，但没有提前定义`` ftp2的实体，没有为其绑定TCP代理和节点，Tcl解释器 start 运行到对应行时 debug 找不到该变量，$ns at 直接抛出错误。

二选一修复： #

• 不需要第二路 $ftp2 流：直接删除以下两行即可

$ns at 0.5 "$ftp1  `cwnd` start"
$ns at 0.1 "$ftp2  `cwnd` start"
$ns at 5. "$ftp2 stop"

• 需要第二 $ftp2 流：在 $tcp1 trace cwnd 这行之后添加如下 $ftp2 的完整定义：

# 第二路TCP代理 绑定n2
set `$tcp2`  [new Agent/TCP/Vegas]
$ns  attach-agent $n2 `$tcp2`
#  `debug` 第二路TCP  `CWND`  第二路TCP接收端 绑定n8
set `$sink2` [new  `$`  Agent/TCPSink]
`$ns`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `exchange`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `stack`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `Sairaj`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `Chonche`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`  `$`