Description:

    This network consists of 4 nodes (Client1, Client2, Router1, Rounter2 and Endserver1). The duplex links between Client1 Client2 and Router1have 2 Mbps of bandwidth and 100 ms of delay. The duplex link between Router1 and Router2 has 2Mbps of bandwidth and 100 ms of delay. The duplex link between Router2 and Endserver1 has 200Kbps of bandwidth and 100 ms of delay. Each link uses a Drop Tail queue. A "TCP" agent is attached to Client1, and Client2. "TCPSink" agent is attached to Endserver1. Both the agents are connected. As default, the maximum size of a packet that a "TCP" agent can generate is 1000bytes. A "TCPSink" agent generates and sends ACK packets to the sender (tcp agent) and frees the received packets. The ftp is set to start at 0.5 sec and stop at 5.5 sec.

File name: “tcpred1.tcl”

#-------Event scheduler object creation--------#

set ns [new Simulator]

#----------creating nam objects----------------#

set nf [open tcpred1.nam w]
$ns namtrace-all $nf

#open the trace file
set nt [open tcpred1.tr w]
$ns trace-all $nt

set proto rlm

$ns color 1 blue
$ns color 2 yellow
$ns color 3 red
 
#---------- creating client- router- end server node----------------#
set Client1 [$ns node]
set Client2 [$ns node]
set Router1 [$ns node]
set Router2 [$ns node]
set Endserver1 [$ns node]

#---creating duplex link---------#

$ns duplex-link $Client1 $Router1 2Mb 100ms DropTail
$ns duplex-link $Client2 $Router1 2Mb 100ms DropTail
$ns duplex-link $Router1 $Router2 2Mb 100ms DropTail
$ns duplex-link $Router2 $Endserver1 200Kb 100ms DropTail

#----------------creating orientation------------------#

$ns duplex-link-op $Client1 $Router1 orient down
$ns duplex-link-op $Client2 $Router1 orient right
$ns duplex-link-op $Router1 $Router2 orient right
$ns duplex-link-op $Router2 $Endserver1 orient down

#------------Labelling----------------#

$ns at 0.0 "$Client1 label Client1"
$ns at 0.0 "$Client2 label Client2"
$ns at 0.0 "$Router1 label Router1"
$ns at 0.0 "$Router2 label Router2"
$ns at 0.0 "$Endserver1 label Endserver1"

#-----------Configuring nodes------------#

$Endserver1 shape hexagon
$Router1 shape square
$Router2 shape square

#----------------Establishing queues---------#

$ns duplex-link-op $Client1 $Router1 queuePos 0.1
$ns duplex-link-op $Client2 $Router1 queuePos 0.1
$ns duplex-link-op $Router1 $Router2 queuePos 0.1
$ns duplex-link-op $Router2 $Endserver1 queuePos 0.5

#---------Establishing communication-------------#
#-------------Client1 to Endserver1---#

set tcp0 [new Agent/TCP]
$tcp0 set maxcwnd_ 16
$tcp0 set fid_ 1
$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"
$ns at 5.5 "$ftp0 stop"

set tcp1 [new Agent/TCP]
$tcp1 set maxcwnd_ 16
$tcp1 set fid_ 2
$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 tcp
$tcp1 tracevar cwnd_

$ns at 0.5 "$ftp1 start"
$ns at 5.5 "$ftp1 stop"

#---------finish procedure--------#

proc finish {} {
         global ns nf nt
         $ns flush-trace
         close $nf     
         close $nt     
        
         puts "running nam..."
         exec nam tcpred1.nam &
         exit 0
      }

#Calling finish procedure

$ns at 6.0 "finish"
$ns run

#-------- How to run-----------#

$ns tcpred2.tcl

#---------- snapshot-----------#