Network Simulator

What is Simulator?

A machine with similar set of controls designed to produce a realistic imitation of the

operation of vehicle, aircraft etc. Simulation is the imitation of operation of a real world process

or system over time.

Network simulation:

It is the technique where a program models the behavior of a network either by

calculating the interaction between the different network entities, their transmission range, their

performance etc.

Network simulator:

It is the piece of software or hardware that predicts the behavior of network, without any actual

network being present.

Type of Network Simulator:

Their types is majorly based on:

Commercial Vs open source.

Simple Vs Complex

Commercial Vs open Source:

Commercial simulators will not provide the source code of it software. All users have to

pay to get the license for their own specific usage requirement. Eg: Opnet, QualNet

Open source simulators are open and any one can use it. The interface is also open for

future development.it reflects new development fastly. Eg:NS2, NS3, OMNET++,

J-SIM,SSFNET.

Simple Vs Complex:

Simple simulators can be used to represent network topology, specify nodes, links &

traffic etc.

Complex simulators allow us to specify protocols used to process network traffic.

Graphical application allows user to easily visualize the working of their simulated

environment.

Let’s now see basic idea about the open source NS2.

NS2 (Network Simulator version 2):

NS2 is the popular, flexible, fast, accurate, free and open source discrete event and

object oriented network simulator. Work on NS2 began in 1989 & in 1995 it was supported by

DARPA, USA. NS2 is originally based on REAL network simulator.

Features of NS2:

It is Object-Oriented.

Discrete event driven network simulator which was originally developed at University of

California-Berkley.

The Programming language used here is C++ & OTCL.

Linkage of C++ and OTCL in NS2:

OTCL acts as front end.

C++ acts as backend running the actual simulation.

OTCL create and configure a network.

C++ is fast to run but slow to change. OTCL is slow to run but fast to configure. So, NS2

combines those two to have a better performance.

About Animation window:

This animation window named “nam” displays the simulation of the network. This simulation is

done with the help of TCL script file which will be saved by the extension “.tcl”.

The command used to run the TCL file is as follows:

ns sample.tcl

Where sample.tcl is the TCL script file.

After compilation of this TCL file the trace file with the extension “.tr” will be created.

This trace file will consist of traced data during transmission in various networks.

XGraph Utility:

The XGraph program draws a graph on an X display given data read from either data

files or from standard input if no files are specified. It can display up to 64 independent data sets

using different colors and/or line styles for each set.

NSG –Network Simulation Generator .It it the Java-based application and open source which

helps in easy creation of simulation by its GUI.

Thus, the open source NS2 have paved a simple way to work on the network and also helpful to

researchers by easily simulating the network and also to overcome the challenges in this field.

The NS3 is the next version of Network Simulation with advanced features.

By,

I.Madhumithah II M.Sc(CS).,