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ns2_reference.md

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CHEATSHEET FOR NS2

NS2 is an event-driven Network Simulator. Event-driven means, we have to put events on the simulation timeline and move along the timeline and actions are taken while confronting an event.

Event -> what happens
Handler -> what to do
An event is associated with a handler.

Dispatching time

Time when the event is scheduled to occur (firing time, executing time) / stored in the variable "time_" of each event.

Each simulation has exactly one scheduler!

create a simulator object / setting a variable

set x 20         
set ns [new Simulator]

unset a variable

unset x

use the variable value

b=x

set b $x

basic arithmetic operations

set x 20
set y 32
expr $x + $y   // x + y = 52

conditional statement

if  [ expr  condition ]
{
	if – body
}

while loop

while
{
	condition
}
{
	while-body
}

for loop

for  {  initialization }  {  condition }  { increment/decrement }
{
	Loop body
}

functions

  • used to combine multiple commands into a new command
proc   < procedure name >
{ }
{
	procedure body
}

proc factorial fact {
 
    if {$fact <= 1} {
 
        return 1
    }
expr $fact * [factorial [expr $fact-1]]
}

setting colours

$ns color "#FF0000"
$ns color "#FFFFFF"

file handling in TCL

set fp [open filename r]
set data [read $fp]
close $fp
set fp1 [open filename w]
puts $fp1 "writing to a file"
close $fp1

call a subprocess within another process (exec)

exec rm $fp

create a trace file

  • A trace file is used to store the coverage info or overall network info
  • To generate a trace file, first create a trace file using OTcl Script
set tracefile [open wired.tr w]
$ns trace-all $tracefile

create a animation info or nam file

  • Nam stands for Network Animator.
  • It supports packet transmission, topology, data inspection, etc
  • During the inspection, it supports animation
set namfile [open wired.nam w]
$ns namtrace-all $namfile

create 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]

create link

droptail means dropping the tail

$ns duplex-link $n0 $n1 5Mb 2ms DropTail
$ns duplex-link $n1 $n2 10Mb 6ms DropTail
$ns duplex-link $n1 $n4 3Mb 2ms DropTail
$ns duplex-link $n4 $n3 100Mb 2ms DropTail
$ns duplex-link $n4 $n5 4Mb 10ms DropTail

setting Queue limit

$ns queue-limit $n1 $n4 2

creation of agents

set udp [new Agent/UDP]
set null [new Agent/Null]
$ns attach-agent $n0 $udp
$ns attach-agent $n3 $null
$ns connect $udp $null

creation of TCP agent

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $n2 $tcp
$ns attach-agent $n5 $sink
$ns connect $tcp $sink

creation of Application CBR, FTP

set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
set ftp [new Application/FTP]
$ftp attach-agent $tcp

start Traffic

$ns at 1.0 "$cbr start"    //schedule an event
$ns at 2.0 "$ftp start"

$ns at 10.0 "finish"   
proc finish {} {
	global ns tracefile namfile
	$ns flush-trace
        #exec xgraph out0.tr out1.tr out2.tr -geometry 800x400 &
	close $tracefile
	close $namfile
	exit 0
}

puts "Simulation is starting"
$ns run   // start the scheduler

RESOURCES & REFERENCES