In the wired network, a link between any two nodes can be broken to demonstrate the link failure. In real time applications such as online games, video conferencing, telephony, and trading systems, link failure occurs due to several reasons. Such link failure even if it exists only for a short period, it leads to unbearable performance degradations. In simulation, the link between any two nodes can be failed and recovered using the command “rtmodel-at” along with keyword “down” and “up” respectively and with the time specification. The test4.tcl illustrates the link failure between two nodes in the wired network.
# Filename: test4.tcl
# —————-ESTABLISHING COMMUNICATION ————-#
#——–CLIENT1 TO ENDSERVER ————-#
set tcp0 [new Agent/TCP]
$tcp0 set maxcwnd_ 16
$tcp0 set fid_ 4
$ns attach-agent $Client1 $tcp0
set sink0 [new Agent/TCPSink]
$ns attach-agent $Endserver1 $sink0
$ns connect $tcp0 $sink0
set ftp0 [new Application/FTP]
$ftp0 attach-agent $tcp0
$ns add-agent-trace $tcp0 tcp
$tcp0 tracevar cwnd_
$ns at 0.5 "$ftp0 start"
$ns at 28.5 "$ftp0 stop"
# —————-CLIENT2 TO ENDSERVER1 ————-#
set tcp1 [new Agent/TCP]
$tcp1 set fid_ 2
$tcp1 set maxcwnd_ 16
$ns attach-agent $Client2 $tcp1
set sink1 [new Agent/TCPSink]
$ns attach-agent $Endserver1 $sink1
$ns connect $tcp1 $sink1
set ftp1 [new Application/FTP]
$ftp1 attach-agent $tcp1
$ns add-agent-trace $tcp1 tcp1
$tcp1 tracevar cwnd_
$ns at 0.58 "$ftp1 start"
$ns at 28.5 "$ftp1 stop"
# —————- CLIENT3 TO ENDSERVER ————-#
set tcp2 [new Agent/TCP]
$tcp2 set fid_ 0
$tcp2 set maxcwnd_ 16
$tcp2 set packetsize_ 100
$ns attach-agent $Client3 $tcp2
set sink2 [new Agent/TCPSink]
$ns attach-agent $Endserver1 $sink2
$ns connect $tcp2 $sink2
set ftp2 [new Application/FTP]
$ftp2 attach-agent $tcp2
$ns add-agent-trace $tcp2 tcp2
$tcp2 tracevar cwnd_
$ns at 0.65 "$ftp2 start"
$ns at 28.5 "$ftp2 stop"
#——————–CLIENT4 TO ENDSERVER—————-#
set tcp3 [new Agent/TCP]
$tcp3 set fid_ 3
$tcp3 set maxcwnd_ 16
$tcp2 set packetsize_ 100
$ns attach-agent $Client4 $tcp3
set sink3 [new Agent/TCPSink]
$ns attach-agent $Endserver1 $sink3
$ns connect $tcp3 $sink3
set ftp3 [new Application/FTP]
$ftp3 attach-agent $tcp3
$ns add-agent-trace $tcp3 tcp3
$tcp3 tracevar cwnd_
$ns at 0.60 "$ftp3 start"
$ns at 28.5 "$ftp3 stop"
#———— Link Failure ————–#
$ns rtmodel-at 2.880511 down $Router3 $Router4
#———— Link Failure Recovery ————–#
$ns rtmodel-at 5.880511 up $Router3 $Router4
Link Failure
Link Failure Recovery
