TCP newreno

The code depicts the action of Newreno and the various changes are implemented in the packet rate and in RTT. To purposefully induce congestion in the network.
For complete description of the TCP newreno go through the link Newreno 
The complete RFC paper can be found here RFC 6582

set ns [new Simulator]
set nf [open mi.nam w]
$ns namtrace-all $nf

set newr [open R.tr w]

set tf [open mi.tr w]
$ns trace-all $tf

proc finish { } {
global ns nf tf
$ns flush-trace
close $nf
close $tf
exec nam mi.nam &
exit 0
}

set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
$n3 label "destination"

$ns duplex-link $n0 $n2 10Mb 1ms DropTail
$ns duplex-link $n1 $n2 1Mb 100ms DropTail
$ns duplex-link $n2 $n3 1Mb 100ms DropTail


set tcp0 [new Agent/TCP/Newreno]
$ns attach-agent $n0 $tcp0

set ftp0 [new Application/FTP]
$ftp0 set packet_Size_ 500
$ftp0 set interval_ 0.005
$ftp0 attach-agent $tcp0

set tcp1 [new Agent/TCP/Newreno]
$ns attach-agent $n1 $tcp1

set ftp1 [new Application/FTP]
$ftp1 set packet_Size_ 1000
$ftp1 set interval_ 0.05
$ftp1 attach-agent $tcp1

set sink0 [new Agent/TCPSink]
$ns attach-agent $n3 $sink0

set sink1 [new Agent/TCPSink]
$ns attach-agent $n3 $sink1

$ns connect $tcp0 $sink0
$ns connect $tcp1 $sink1

$ns at 0.1 "$ftp0 start"
$ns at 0.1 "$ftp1 start"
# ####################################################################
# plotWindow(tcpSource,file): write CWND from $tcpSource
#                       to output file $file every 0.1 sec
  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"
  }
# ####################################################################
# Start plotWindow
 $ns at 0.1 "plotWindow $tcp0 $newr"

# ####################################################################
$ns at 10.0 "finish"
$ns run

The code contains parts which are written in red to specify their use, which is to plot the congestion window and the time to an output file.
Here puts command used to write content into file and the following graph is obtained when plotted with help of xgraph tool.