Introduction to Network Simulators

A network simulator is a piece of software or
hardware that predicts the behavior of a
network, without an actual network being
Network simulators serve a variety of needs.
Compared to the cost and time involved in
setting up an entire test bed containing
multiple networked computers, routers and
data links, network simulators are relatively
fast and inexpensive
allow engineers to test scenarios that might
be particularly difficult or expensive to
emulate using real hardware
◦ simulating the effects of a sudden burst in traffic
◦ a DoS attack on a network service
◦ test new networking protocols or changes to
existing protocols in a controlled and reproducible
With the help of simulators one can design
hierarchical networks using various types of
nodes like computers, hubs, bridges, routers,
optical cross-connects, multicast routers,
mobile units, MSAUs etc
Various types of Wide Area Network (WAN)
technologies like TCP, ATM, IP etc and Local
Area Network (LAN) technologies like
Ethernet, token rings etc. can all be simulated
with a typical simulator
the user can test, analyze various standard
results apart from devising some novel
protocol or strategy for routing etc
a network simulator must enable a user to
represent a network topology,
specifying the nodes on the network,
the links between those nodes
and the traffic between the nodes
More complicated systems may allow the user to
specify everything about the protocols used to
handle network traffic.
Graphical applications allow users to easily
visualize the workings of their simulated
Text-based applications may provide a less
intuitive interface, but may permit more
advanced forms of customization.
Others, such as GTNets, are programmingoriented, providing a programming
framework that the user then customizes to
create an application that simulates the
networking environment to be tested.
Ns2- Command based
Opnet- Graphical
OPNET solutions address application performance management;
network planning, engineering, and operations; and network R&D.
OPNET solutions for Network engineering, operations, and planning
include the following
◦ IT Guru Network Planner helps enterprises plan their network for new
applications or technologies.
◦ SP Guru Network Planner and SP Guru Transport Planner optimize service
provider network designs for capacity, cost, QoS, and survivability.
◦ Sentinel is OPNET's network configuration auditing solution and it is used
to ensure network integrity, security, and policy compliance.
◦ NetMapper complements OPNET's Sentinel and Guru solutions by
automatically creating content-rich network diagrams in Microsoft Visio
◦ OPNET nCompass, a software solution for the NOC, enables operators to
visualize real-time network topology, traffic, events, and status in a single
OPNET Modeler, a network modeling and simulation software
solution, is one of OPNET's flagship solutions and also its oldest
Global Mobile Information System Simulator
(GloMoSim) is a network protocol simulation
software that simulates wireless and wired
network systems.
GloMoSim is designed using the parallel
discrete event simulation capability provided
by Parsec, a parallel programming language.
GloMoSim currently supports protocols for a
purely wireless network.
It uses the Parsec compiler to compile the
simulation protocols.
ns was built in C++ and provides a simulation
interface through OTcl, an object-oriented
dialect of Tcl.
The user describes a network topology by writing
OTcl scripts, and then the main ns program
simulates that topology with specified
The NS2 makes use of flat earth model in which it
assumes that the environment is flat without any
elevations or depressions. However the real world
does have geographical features like valleys and
mountains. NS2 fails to capture this model in it.