issa sariyayakul ul part i: nspart i: ns2 basics tee ns2teerawat/publications/ns2/w01-network...

Part I: NSPart I: NS22 BasicsBasicsPart I: NSPart I: NS22 BasicsBasicsPart I: NSPart I: NS2 2 BasicsBasicsPart I: NSPart I: NS2 2 BasicsBasics

Textbook: T. Issariyakul and E. Hossain, Introduction to Network Simulator NS2, Springer 2008. 1

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Part I: OutlineTh B i• The Basics– Simulation of computer networks– Tcl/OTcl Tutorial– Tcl/OTcl Tutorial

• NS2 FundamentalsNS2 Fundamentals– An introduction to NS2– Linkage Between OTcl and C++ in NS2– Random Number Generators– Event Driven Simulation in NS2

NS2 Main Network Components– NS2 Main Network Components


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Simulation of Computer NetworksSimulation of Computer NetworksSimulation of Computer NetworksSimulation of Computer NetworksSimulation of Computer NetworksSimulation of Computer NetworksSimulation of Computer NetworksSimulation of Computer Networks


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Outline• Computer Networks

A Study of Computer Networks• A Study of Computer Networks• Time-Dependent Simulationp• Example


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Computer Networks• Computer + Networking

NetworkingNetworking


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Computer Networks• Generally, there are so many tasks• Layering Concept: SeparateLayering Concept: Separate

functionalityOSI M d l TCP/IP M d l– OSI Model - TCP/IP Model

Application

TSession

Presentation

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Application

Data LinkNetwork

Transport

Data LinkNetwork

Transport

Textbook: T. Issariyakul and E. Hossain, Introduction to Network Simulator NS2, Springer 2008.PhysicalData Link

PhysicalData Link

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A Study of Computer Networks• Suppose you devise a great protocol.

How do you show that it’s great?How do you show that it s great?– Experiment: Put all routers together

d l t l s thand let people use them– Mathematic model: Model routers using

h ha graph theory– Simulation: Use programming (e.g., C++ p g g ( g

or NS2) to represent routers


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A Study of Computer Networks

Pros Cons

Experiment Realistic Expensive/ Sometime not possible

M h i I i h N d kMathematic Model

Insight Need to make assumptions

Simulation •Easy (Cheap)•Used for verification

Not much insight, sometimes need to

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Time-Dependent Simulation

• Most commonly-usedy• Simulation proceeds chronologically.

T i t• Two main types:– Time-Driven Simulation– Event-Driven Simulation


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Time-Driven Simulation• Observe the system at a fixed interval.• Event occurs within an interval is assumed to

occur at the end of the interval• Suppose an interval = � seconds. Then the

simulation proceeds as follows:

– a,b,c,d are eventsi d 2– a is assume to occurred at t= 2�

– b,c are assume to occurred at t=( 5� )• The simulation finishes at a pre specified time

Textbook: T. Issariyakul and E. Hossain, Introduction to Network Simulator NS2, Springer 2008.

• The simulation finishes at a pre-specified time.10

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E nt D i n Sim l ti nEvent-Driven Simulationb• Observe every event.

• Each event provide a reference to the next event (e.g.,Each event provide a reference to the next event (e.g., using pointer)

a b cNext_event Next_event Next_event

• Simulation finishes– At a pre-specified time– When there is no more event

Textbook: T. Issariyakul and E. Hossain, Introduction to Network Simulator NS2, Springer 2008.

When there is no more event

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Example: Queuing System


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Summary• Computer Networks = Computer + Networking• A Study of Computer NetworksA Study of Computer Networks

– Experimental– Mathematical Model– Mathematical Model– Simulation

Tim D p d t Sim l ti• Time-Dependent Simulation– Time-Driven Simulation

E D l– Event-Driven Simulation• Example: A queuing system


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issa sariyayakul ul part i: nspart i: ns2 basics tee ns2teerawat/publications/ns2/w01-network...

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