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CARRIER SENSE MULTIPLE ACCESS

     CARRIER SENSE MULTIPLE ACCESS

Aim:
       To write an ns2 program for implementing carrier sense multiple access.

Algorithm:

Step 1: start the program.
Step 2: declare the global variables ns for creating a new simulator.
Step 3: set the color for packets.
Step 4: open the network animator file  in the write mode.
Step 5: open the trace file and the win file in the write mode.
Step 6:  transfer the packets in network.
Step 7: create the capable no of nodes.
Step 8: create the duplex-link between the nodes including the delay time,bandwidth and dropping                                               .            queue mechanism.
Step 9: give the position for the links between the nodes.
Step 10: set a tcp connection for source node.
Step 11: set the destination node using tcp sink.
Step 12: set the window size and the packet size for the tcp.
Step 13: set up the ftp over the tcp connection.
Step 14:.set the udp and tcp connection for the source and destination.
Step 15: create the traffic generator CBR for the source and destination files.
Step 15: define the plot window and finish procedure.
Step 16: in the definition of the finish procedure declare the global variables.
Step 17: close the trace file and namefile and execute the network animation file.
Step 18: at the particular time call the finish procedure.
Step 19: stop the program.




Program:

set ns [new Simulator]
$ns color 1 blue
$ns color 2 red
set fi1 [open out.tr w]
set winfile [open WinFile w]
$ns trace-all $fi1
set fi2 [open out.nam w]
$ns namtrace-all $fi2
proc finish {} {
global ns fi1 fi2
$ns flush-trace
close $fi1
close $fi2
exec nam out.nam &
exit 0
}
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]
set n5 [$ns node]
$n1 color red
$n1 shape box
$ns duplex-link $n0 $n2 2Mb 10ms DropTail
$ns duplex-link $n1 $n2 2Mb 10ms DropTail
$ns simplex-link $n2 $n3 0.3Mb 100ms DropTail
$ns simplex-link $n3 $n2 0.3Mb 100ms DropTail
set lan [$ns newLan "$n3 $n4 $n5" 0.5Mb 40ms LL Queue/DropTail MAC/Csma/Cd Channel]
set tcp [new Agent/TCP/Newreno]
$ns attach-agent $n0 $tcp
set sink [new Agent/TCPSink/DelAck]
$ns attach-agent $n4 $sink
$ns connect $tcp $sink
$tcp set fid_ 1
$tcp set window_ 8000
$tcp set packetsize_ 552
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ftp set type_ FTP
set udp [new Agent/UDP]
$ns attach-agent $n1 $udp
set null [new Agent/Null]
$ns attach-agent $n5 $null
$ns connect $udp $null
$udp set fid_ 2
set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
$cbr set type_ CBR
$cbr set packet_size_ 1000
$cbr set rate_ 0.01mb
$cbr set random_ false
$ns at 0.1 "$cbr start"
$ns at 1.0 "$ftp start"
$ns at 24.0 "$ftp stop"
$ns at 24.5 "$cbr stop"
proc plotwindow { tcpSource file } {
global ns
set time 0.1
set now [$ns now]
set cwnd [$tcpSource set cwnd_]
set wnd [$tcpSource set window_]
puts $file "$now $cwnd"
$ns at [expr $now+$time] "plotwindow $tcpSource $file"
}
$ns at 1.0 "plotwindow $tcp $winfile"
$ns at 5 "$ns trace-annotate \"packet drop\""
$ns at 125.0 "finish"
$ns run


















Output: