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set ns [new Simulator]
#open a namtrace file
set nf [open main.nam w]
$ns namtrace-all $nf

#open a trace file
set nt [open main.tr w]
$ns trace-all $nt
#Define a 'finish' procedure
proc finish {} {
global ns nf nt
$ns flush-trace
close $nf
close $nt
exec nam p2.nam &
exit 0
}
#Create six nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]
set n5 [$ns node]
#connect the nodes with two links
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
$ns duplex-link $n2 $n1 1Mb 10ms DropTail
$ns duplex-link $n3 $n1 1Mb 10ms DropTail
$ns duplex-link $n4 $n1 1Mb 10ms DropTail
$ns duplex-link $n5 $n1 1Mb 10ms DropTail
#set queue length
$ns queue-limit $n0 $n1 5
$ns queue-limit $n2 $n1 2
$ns queue-limit $n3 $n1 5
$ns queue-limit $n4 $n1 2
$ns queue-limit $n5 $n1 2
#Label the nodes
$n0 label "ping0"
$n1 label "Router"
$n2 label "ping2"
$n3 label "ping3"
$n4 label "ping4"
$n5 label "ping5"
#color the flow
$ns color 2 Blue
$ns color 3 Red
$ns color 4 Yellow
$ns color 5 Green

#Define a 'recv' function for the class 'Agent/Ping'
Agent/Ping instproc recv {from rtt} {
$self instvar node_
puts "node [$node_ id] received ping answer from \ $from with round-trip-time $rtt ms."
}
#create ping agents and attach them to the nodes
set p0 [new Agent/Ping]
$ns attach-agent $n0 $p0
$p0 set class_ 1
set p2 [new Agent/Ping]
$ns attach-agent $n2 $p2
$p2 set class_ 2
set p3 [new Agent/Ping]
$ns attach-agent $n3 $p3
$p3 set class_ 3
set p4 [new Agent/Ping]
$ns attach-agent $n4 $p4
$p4 set class_ 4
set p5 [new Agent/Ping]
$ns attach-agent $n5 $p5
$p5 set class_ 5
#connect the two agents
$ns connect $p0 $p5
$ns connect $p4 $p5
proc SendPingPacket {} {
global ns p0 p4
set intervalTime 0.001
set now [$ns now]
$ns at [expr $now+$intervalTime] "$p0 send"
$ns at [expr $now+$intervalTime] "$p4 send"
$ns at [expr $now+$intervalTime] "SendPingPacket"
}
$ns at 0.1 "SendPingPacket"
$ns at 2.0 "finish"
$ns run