Transcript Chapter 1 - William Stallings, Data and Computer Communications

Introduction to Network
Simulators
Lecture 1
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 What's Network Simulation
Simulation is one of the most widely used
techniques in network design and management to
predict the performance of a network system or
network application before the network is physically
built or the application is rolled out
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 Network Simulator
A network simulator is a piece of software or
hardware that predicts the behavior of a
network, without an actual network being
present.
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 ns --- what is it good for?
Used to:
•
•
•
Evaluate performance of existing
network protocols.
Prototyping and evaluation of new protocols.
Large-scale simulations not possible
in real experiments.
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 Advantages of Network Simulator
• 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
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 Advantages of Network Simulator (cont)
• 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 environment
• With the help of simulators one can design
hierarchical networks using various types of nodes
like computers, hubs, bridges, routers, optical crossconnects, multicast routers, mobile units, MSAUs
etc
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 Types of network simulators
• 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
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 Types of network simulators (cont)
 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.
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 Graphical applications allow users to easily
visualize the workings of their simulated
environment.
 Text-based applications may provide a less
intuitive interface, but may permit more advanced
forms of customization.
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 Examples of Network Simulators
• Ns2- Command based
• Opnet- Graphical
• OMNET++
• QualNet
• GlomoSim
• Cisco Packet tracer
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 Opnet
 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
format.
◦ OPNET nCompass, a software solution for the NOC, enables operators to
visualize real-time network topology, traffic, events, and status in a single
view.
 OPNET Modeler, a network modeling and simulation software solution,
is one of OPNET's flagship solutions and also its oldest product
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‫‪ OPNET Scenarios‬‬
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 GloMoSim
 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.
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 ns2
 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 parameters.
 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.
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‫‪ NS2 Scenario‬‬
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