An Introduction to Network Simulator

Dr. Ajit K NayakDept of CSIT, ITER

S‘O’A University, BBSR

Part II

• Introducing OTcl

• Working with NS2

Basics of OTcl - I• Class is used to register a class name.

– Unlike C++, there is no class body where all members of the class are declared/defined.

– i.e. once the class is registered, the member functions and data members can be declared anywhere in the

script with the use of the class name and self variable.

• instproc is used to define a member function.

• init is the name of constructor.

• self is equivalent to the ‘this’ keyword of C++.

• instvar is used to declare a data member.

• superclass is used to specify the parent class in case of inheritance.

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Basics of OTcl - II

• Object initialization:– set ctr [ new Counter ]

• ctr is an object of class Counter

• It calls the constructor to initialize the instance variables.

• Method invocation:– $ctr increment

• invokes the method increment of class Counter

– puts [ $ctr getValue ] • invokes the method getValue of class Counter and

prints the value returned from the member function

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Example – Class-Object (I)# Create a class called "mom" and add a member function called

"greet"

Class Mom

Mom instproc greet {} {

$self instvar age

puts “$age years old mom say: \n\tHow are

you doing?”

}# Create a child class of "mom" called "kid" and override the

member function "greet"

Class Kid -superclass Mom

Kid instproc greet {} {

$self instvar age

puts “$age years old kid say: \n\tWhat’s

up, dude?”

}

Example – Class-Object (II)

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# Create a mom and a kid object & set age for each

set mom [new Mom]

$mom set age 45

set kid [new Kid]

$kid set age 15# Calling member function "greet" of each object

$mom greet

$kid greetOutput:

45 year old mom say:

How are you doing?

15 year old kid say:

what’s up dude?

Task I• Execute the previous OTcl program.

• Fill in the spaces provided to complete the OTcl program below, execute the program and note the output

Class Real

Real instproc init {x} { # constructor

$self instvar value

set value $x

}

Real instproc multiply { x } {

... FILL IN: multiply val and x then print ...

}

Real instproc divide {x} {

$self instvar value

... FILL IN: divide val and x then print result...

} NS-2/AN/Intro/ 8

Task I contd.Class Integer -superclass Real

Integer instproc divide {x} {

... FILL IN ...

}

set realA [new Real 12.3]

set realB [new Real 0.5]

$realA multiply $realB

$realA divide $realB

set integerA [new Integer 12]

set integerB [new Integer 5]

$integerA multiply $integerB

$integerA divide $integerB

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NS2 Programming Structure

• Create the event scheduler

• Turn on tracing

• Create network topology

• Create transport connections

• Generate traffic

– Traffic source

– Traffic sink

– Connection between source & sink

• Run the simulation

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Creating the event scheduler

• Create event scheduler

– set ns [new Simulator]

• Schedule an event

– syntax: $ns at <time> <event>

– $ns at 5.0 “finish”

• Start Scheduler

– $ns run

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proc finish {} {

global ns nf

close $nf

exec nam out.nam &

exit 0

}

Tracing (outputs)• Packet/Event Trace

– $ns trace-all[open out.tr w]

• NAM Trace (Network Animator)

– set nf [open out.nam w]

– $ns namtrace-all $nf

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Creating topology(Two nodes connected by a link)

• Creating nodes

– set n0 [$ns node]

– set n1 [$ns node]

• Creating link between

nodes

– syntax: $ns <link_type> <node1> <node2> <bandwidth> <delay> <queueType>

– $ns duplexlink $n0 $n1 1Mb 10ms DropTail

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Program for two node network1. Create a file named

twoNode.tcl and add the

following contents in it.

set ns [new Simulator]

set nf [open twoNode.nam w]

$ns namtrace-all $nf

set n0 [$ns node]

set n1 [$ns node]

$ns duplex-link $n0 $n2 100Mb 5ms DropTail

$ns run

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2. Save and exit from the editor,

Now execute the program with

following command in command

line

ns twoNode.tcl

3. This will generate

twoNode.nam. To see the

visualization, issue the following

command in command line

nam twoNode.nam &

Color• Nodes Colour:

– $node color blue ;#creates a blue color node

– (Other colors are red, green, chocolate etc.)

• Node Shape:– $node shape box ;#creates a square

shaped node

– (Other shapes are circle, box, hexagon )

• $n0 add-mark m0 blue box ;# creates a concentric circle over node n0

• $ns at 2.0 \$n0 delete-mark m0" ;# deletes the mark at simulation time 2 sec.

• Node Label:– $n0 label Router ;# labels n0 as a Router

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• Link Colour:

• $ns duplex-link-op $n0 $n1 color \green"

link from n0 to n1 becomes green

• Link Label:

• $ns duplex-link-op $n0 $n1 label \point-to-point“

link is labelled as point-to- point

• Link Orientation:

• $ns duplex-link-op $n(0) $n(1) orient right

the link is drawn horizontally from n0 to n1

• $ns duplex-link-op $n(1) $n(2) orient left

• ( up, down, right-up, left-down, 60deg)

Task II• Execute the twoNode.tcl

• Create a ring network of 3 nodes with adjacent nodes of different color and red color links between them.

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Sending data (UDP)

• Create UDP source agent (transport connection)– set udp [new Agent/UDP]

– $ns attach-agent $n0 $udp

• Create UDP sink agent– set null [new Agent/Null]

– $ns attach-agent $n1 $null

• Connect two transport (source-sink) agents– $ns connect $udp $null

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Sending data contd.• Create CBR traffic source on the top of UDP

agent (Application)

– set cbr [new Application/Traffic/CBR]

– $cbr attach-agent $udp

• Start and stop of data transmission

– $ns at 0.5 “$cbr start”

– $ns at 4.5 “$cbr stop”

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Complete Programset ns [new Simulator]

set n0 [$ns node]

set n1 [$ns node]

$ns trace-all [open

twoNode.tr w]

set nf [open twoNode.nam w]

$ns namtrace-all $nf

$ns duplex-link $n0 $n1

100Kb 10ms DropTail

set udp [new Agent/UDP]

$ns attach-agent $n0 $udp

set null [new Agent/Null]

$ns attach-agent $n1 $null

$ns connect $udp $null

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set cbr [new

Application/Traffic/CBR]

$cbr attach-agent $udp

$ns at 0.1 “$cbr start”

$ns at 2.35 “$cbr stop”

$ns at 2.4 “finish”

proc finish {} {

global nf ; close $nf

exec nam twoNode.nam &

exit 0

}

$ns run

Sending data (TCP)• Create TCP agent and attach it to the node

– set tcp0 [new Agent/TCP]

– $ns attach-agent $n0 $tcp0

• Create a Null Agent and attach it to the node– set null0 [new Agent/TCPSink]

– $ns attach-agent $n1 $null0

• Connect the agents– $ns connect $tcp0 $null0

• Trafic on the top of TCP (FTP or Telnet)

– set ftp [new Application/FTP]

– $ftp attach-agent $tcp0 OR

– set telnet [new Application/Telnet]

– $telnet attach-agent $tcp0

Task III

1)Execute modified twoNode.tcl

and observe the animation

output.

2) Excute the same usng TCP and

ftp .

Output? (twoNode.tr)+ 1 0 1 cbr 500 ------- 0 0.0 1.0 0 0

- 1 0 1 cbr 500 ------- 0 0.0 1.0 0 0

+ 1.005 0 1 cbr 500 ------- 0 0.0 1.0 1 1

- 1.005 0 1 cbr 500 ------- 0 0.0 1.0 1 1

+ 1.01 0 1 cbr 500 ------- 0 0.0 1.0 2 2

- 1.01 0 1 cbr 500 ------- 0 0.0 1.0 2 2

r 1.014 0 1 cbr 500 ------- 0 0.0 1.0 0 0

+ 1.015 0 1 cbr 500 ------- 0 0.0 1.0 3 3

- 1.015 0 1 cbr 500 ------- 0 0.0 1.0 3 3

r 1.019 0 1 cbr 500 ------- 0 0.0 1.0 1 1

+ 1.02 0 1 cbr 500 ------- 0 0.0 1.0 4 4

- 1.02 0 1 cbr 500 ------- 0 0.0 1.0 4 4

r 1.024 0 1 cbr 500 ------- 0 0.0 1.0 2 2

Explaining Output (I)

• Column 1: events– +: enqueue– -: dequeue– r: receive– d: drop

• Column 2: – Time of event

• Column 3 & 4: – Trace between which two nodes?

Explaining Output (II)

• Column 5,6: – Packet type, Packet size

• Column 7-14: – Flags used for ECN (not used here)

• Column 15: – IP flow identifier (IPv6)

• Column 16,17: – Source & Destination address

• Column 18,19: – Sequence number, unique packet identifier

Suggested Readings

• OTcl Tutorials

– http://www.tcl.tk/man/tcl8.5/tutorial/tcltutorial.html

• NS-2 Tutorials

– http://www.isi.edu/nsnam/ns/tutorial

– http://nile.wpi.edu/NS/

– NS Manual

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Thank You

End of Part II