Introduction to NS2

T S Pradeep KumarVIT University- Chennai campushttp://www.pradeepkumar.org

tspembedded@gmail.com

Overview•Linux Vs Windows•Network Simulation •Introduction to NS2•About NS2•NS2 Architecture•OTCL

Linux for NS2

Windows for NS2

Versus

Why not Windows?•Support has been stopped beyond NS-2.27•Package Configuration is tedious•Use NS2 at your own risk

• Verss

Linux for NS2 Fedora (10, 12)

If DVD Version- no need of additional package installation Install all the packages (if default installation selected, then additional packages have to be

installed) Ubuntu (9.04, 9.10, 10.04, 10.10)

Additional packages to be installed, there may be GCC Issues, xgraph and NAM issues Red Hat Enterprise Linux 5 (RHEL5)

Cent OS is the alternative for RHEL Basic commands (ls, chmod, tar, rpm, make, gedit, vi, pwd, passwd, echo, cd, etc) Directory structure and shell prompt Path variables setting, Installation of packages and dependencies

Basic Linux Commands• ls – to list the directory contents• chmod – changing the mode of the file• tar – tape archive (to compress or decompress)• rpm – a type of installation file for linux• make – to compile or recompile in linux• gedit or vi – editors (similar like notepad)• pwd - present working directory • passwd – to change the user passwd• echo – to echo to the screen• cd – change directory• mkdir – to create a directory

Linux basics

• To run the install file within the directory scope• $prompt] ./install

• To run the install file in global scope is – $prompt] install

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Network Simulation• Approaches– Experiment

• Put all network Devices and measure the results/performance• Pros - realistic• Cons - Expensive/Sometime impossible

– Mathematical model• Model devices using a graph model• Insight• Need to make assumptions

– Simulation• Use programming to represent devices• Easy and can be easily verified• Not much insight, need to make assumptions

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Network Simulation

• Network Simulation– Time Driven• Events occurs within the interval is assumed to be

occur at the end of the interval• Simulation finishes at a pre-specified time• a, b,c,d are events• a is assumed to occur at t=2Δ

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Network Simulation• Network Simulation

– Event Driven• Every event provide a reference to the next event (Example: using

pointer)

• Simulation finishes– When there are no more events– At pre-specified time

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A B C

About NS2

• NS is a discrete event simulator • It provides support for – Simulation of TCP– Routing– Multicast Protocols over Wired and Wireless

networks

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About NS2

• NS is not a polished and finished product, but the result of an on-going effort of research and development.

• In particular, bugs in the software are still being discovered and corrected.

• Users of ns are responsible for verifying for themselves that their simulations are not invalidated by bugs

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NS2 Architecture

• Network Simulator 2 is an event driven Simulator

• It consists of – C++ (Internally)– OTCL (User Interface)– TclCL (Interface between C++ and OTCL)

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NS2 Architecture

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NS2 Architecture

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OTCL

• NS is a OTCL interpreter with network simulation object libraries

• Relation between TCL and OTCL is similar to C and C++

• A Simple example follows..• To run these examples– ns filename.tcl (or) tclsh filename.tcl

TCL Example# Writing a procedure called "test“proc test {} {

set a 43set b 27set c [expr $a + $b]set d [expr [expr $a - $b] * $c]for {set k 0} {$k < 10} {incr k} {if {$k < 5} { puts "k < 5, pow = [expr pow($d, $k)]"} else { puts "k >= 5, mod = [expr $d % $k]"} } }

# Calling the "test" procedure created abovetest

OTCL Example

# Create a class call "mom" and add a member function call "greet"Class mommom instproc greet {} { $self instvar age_ puts "$age_ years old mom say: How are you doing?"}

OTCL Example

# Create a child class of "mom" called "kid" and overide the member function "greet"Class kid -superclass momkid instproc greet {} { $self instvar age_ puts "$age_ years old kid say: What's up, dude?"}

OTCL Example

• # Create a mom and a kid object set each age• set a [new mom]• $a set age_ 45• set b [new kid]• $b set age_ 15

• # Calling member function "greet" of each object• $a greet• $b greet

OTCL Example

• class keyword is used to create a class• instproc is used to create a instance procedure

(define a member function)• $self is similar to “this” in C++• instvar checks if the variable is already declared in its

class or superclass. If the variable name given is already declared, the variable is referenced, if not a new one is declared

Lets practice Linux for sometime…..

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