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Network Simulator Tutorial

Sankar.P,

AP\ECE

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Network SimulationMotivation:

Learn

fundamentals ofevaluatingnetwork

performance viasimulation

Overview:

fundamentals of

discrete eventsimulation

ns-2 simulation

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What is simulation?

system boundary

exogenous inputsto system

(the environment)

system under study(has deterministic rulesgoverning its behavior)

real life

Program boundary

pseudo random inputsto system

(models environment)

system under study(has deterministic rulesgoverning its behavior)

simulated life

observer

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Why Simulation?

real-system not available, iscomplex/costly or dangerous (eg:space simulations, flight simulations)

quickly evaluate design alternatives

(eg: different system configurations) evaluate complex functions for which

closed form formulas or numericaltechniques not available

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Simulation:advantages/drawbacks*advantages:

sometimes cheaper

find bugs (in design) in advance

generality: over analytic/numerical techniques

detail: can simulate system details at arbitrary level

drawbacks: caution: does model reflect reality

large scale systems: lots of resources to simulate(especially accurately simulate)

may be slow (computationally expensive 1 minreal time could be hours of simulated time)

art: determining right level of model complexity

statistical uncertainty in results

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History and Status

Columbia NEST

UCB REAL

ns-1 ns-2

ns-3 100K lines of C++

70K lines of OTcl

30K lines of test suite

20K lines of documentation

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What is NS2 Discrete event simulator

A package of tools that simulatesbehavior of networks

Create Network Topologies

Log events that happen under any load

Analyze events to understand thenetwork behavior

Wired and wireless

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NS Software Structure: C++

and OTCL Uses two languages

C++ for packet-processing per packet processing

fast to run, detailed, complete control

OTCL for control

simulation setup, configuration, occasional actions fast to write and change

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OTCL and C++: Duality

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C++ OTcl

Pure C++objects

Pure OTcl

objects

C++/OTcl splitobjects

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Extending the TCL Interpreter

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OTcl: object-orientedTcl

TclCL: C++ and OTcllinkageDiscrete eventscheduler

Data networkcomponents

Link layer and upEmulation support

Tcl

OTcl

TclCLEvent

Scheduler

NetworkComponents

C/C++

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Using NS2

Problem

Simulationmodel

Setup/runsimulation

with ns

Resultanalysis

Modifyns

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NS2 environment

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Simulation setup

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Create event scheduler (Calendar scheduling ).

Turn on tracing.

Create network.

Setup routing and Insert errors.

Create transport connection.

Create traffic.

Transmit application level data.

Trace out the simulated output using trace fileand nam view.

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Simulation Configurations

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Copy the implemented algorithms in to queuefolder in NS2 (nsallinone2.29/ns2.29/queue).

Change the default settings of the file ns-default.tcl

(nsallinone2.29/ns2.29/tcl/lib/ ns-default.tcl).

Change the settings in the Makefile.in for

creating object files. Configure the network using ./configure.

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Cont..

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Make the new environment for simulation.

Write the tcl code for create the networktopology and simulation

Create traffic and analyze the network using

trace and verify the packet flow using networkanimator.

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Wired Network

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Coding(Cont)

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Coding(Cont)

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Coding(Cont)

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Network Created

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OUTPUT

(FLOW

1)

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Output(Flow 2)

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Output (congestion)

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Ou

tpu

t ( Flow 2 Stopped)

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Tracing and MonitoringPacket tracing:

On all links: $ns trace-all [open out.tr w]On one specific link: $ns trace-queue $n0 $n1$tr

-- + 1 0 2 cbr 210 ------- 0 0.0 3.1 0 0

- 1 0 2 cbr 210 ------- 0 0.0 3.1 0 0

r 1.00234 0 2 cbr 210 ------- 0 0.0 3.1 0 0

We have new trace format

Event tracing (support TCP right now)Record event in trace file: $ns eventtrace-allE 2.267203 0 4 TCP slow_start 0 210 1

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Tracing and Monitoring-2Visualize trace in nam

$ns namtrace-all [open test.nam w]$ns namtrace-queue $n0 $n1

Variable tracing in namAgent/TCP set nam_tracevar_ true$tcp tracevar srtt_$tcp tracevar cwnd_

Monitor agent variables in nam$ns add$ns add--agentagent--trace $trace $tcptcp $$tcptcp$ns monitor$ns monitor--agentagent--trace $trace $tcptcp$srm0$srm0 tracevartracevar cwndcwnd__$ns delete$ns delete--agentagent--trace $trace $tcptcp

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Inserting Errors

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Creating Error Module

set loss_module [new ErrorModel]

$loss_module set rate_ 0.01$loss_module unit pkt$loss_module ranvar [newRandomVariable/Uniform]$loss_module drop-target [new Agent/Null]

Inserting Error Module

$ns lossmodel $loss_module $n0 $n1

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Network Dynamics

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Link failuresHooks in routing module to reflect routing changes

Four models$$nsns rtmodelrtmodel TraceTrace $$nn00 $$nn11$$nsns rtmodelrtmodel ExponentialExponential {}

$$nn00

$$nn11$$nsns rtmodelrtmodel DeterministicDeterministic {} $$nn00

$$nn11$$nsns rtmodelrtmodel--atat up|downup|down $$nn00 $$nn11

Parameter list[][] [][]

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Wireless network

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Mobile node Modules

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Cont

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Cont

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Mobile Node Diagram-DSDV

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Mobile Node Diagram-DSR

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Running a simulation scenario

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Setting up variables

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Cont

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Configuring Mobile nodes

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Configuring Movement

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Set up traffic Flow

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Set Stop Time and Start Simulation

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Trace File

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Reading Trace File

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Cont

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Cont

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Wireless support in ns continuouslyevolvingMany other contributed models (not

integrated into ns distribution) include:Mobiwan, GPRS, Bluehoc and blueware, CIMSetcAvailable from ns contributed code page at

http://www.isi.edu/nsnam/ns/nscontributed.html

Marc Greis Tutorial

Support Materials

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Thank You