ns2 network simulator- tutorial for begineers

7/21/2019 Ns2 Network Simulator- Tutorial for Begineers

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Ns2

Network Simulator

Tutorial for Beginners’

Udhay Prakash

Udhayprakash.blogspot.in

Uday3prakash @gmail.com



Presentation Agenda

• Introduction to Linux

• Importance of Open Source software

• Network Simulators

•

• Ns2 Installation

• TCL scripting language

• Introduction to NAM and Xgraph

• Discussion about trace file format

04-Jul-14 2udhayprakash.blogspot.in



Outcomes

• To get ease with Linux platform

• Open Source vs Free ware vs proprietary

• To insight about a Network Simulator

•

• Scripting language vs programming language

• Ability to install ns2, nam and xgraph

• Ease in working with TCL scripting

• Insight to NAM and Trace files




SESSIO -1

Introducing to Linux and s2ntroducing to Linux and s2




Linux

• Developed under GNU project.

• Open Source software, except RedHat

• Major Linux Families» Debian, Ubuntu, Mint, ….

» Fedora

» OpenSUSE

» ArchLinux

» CentOS & RedHat




Working in Linux

• Are you new to Linux Operating System?

• Are you more habituated to Windows or

Macintosh Operating Systems ?

• en, care u y o ow me… (switch on your PCs)

– Creating a file

– Reading/writing/editing a file

– Operating System specific file types




Why Simulators?

• Advantages☺Complex scenarios can be easily tested

☺Cheap-does not require costly equipment

☺Results can be quickly obtained-more ideas can be tested in asmaller timeframe

☺Controlled experimental conditions

☺Repeatability helps aid debugging

• Disadvantages☻Not real

☻Real systems too complex to model

☻Consideration of practical conditions




NS2 Network Simulator

• Open-source event-driven simulator

• Designed specifically for research in computer

communication networks.

• onta ns mo u es or numerous networ

components such as routing, transport layer

protocol, and application.




Ns2 sources

• http://www.isi.edu/nsnam/ns/

– The source code and documentation is currently maintained

by VINT project at ISI

• http://nsnam.isi.edu/nsnam/index.php/Main_Page – ep , : ns- . re ease .

– Mar 10, 2007: ns-2.31 released.

– July 2, 2006: ns-3 project announced.

• NS2 is a discrete event simulator targeted at networking research

• NS2 is an object oriented simulator, written in C++, with an OTcl

interpreter as a frontend




NS2 related Documentation

• introductory: Marc Greis's tutorial

• reference: Ns Manual (formerly called "ns Notes

and Documentation")

• ns y xamp e

• Practical Programming in Tcl and Tk

(http://www.beedub.com/book/)• http://hpds.ee.ncku.edu.tw/~smallko/ns2/ns2.htm




NS2- Features

• Collection of various protocols at multiple layers – tahoe, vegas, sack)

– MAC(802.11, 802.3, TDMA)

– Ad-hoc Routing (DSDV, DSR, AODV, TORA)

– Sensor Network (diffusion, gaf)

– Multicast protocols, Satellite protocols, and TCP(reno, many others• Traffic Models: CBR, VBR, Web, …

• Error Models: Uniform, Busty, …

• Misc: Radio Propagation, Mobility models, Energy Models, …

• Topology Generation tools (nsg2.1, ..)

• Visualization tools (NAM), Tracing

• Codes are contributed from multiple research communities

– Good: Large set of simulation modules

– Bad: Level of support and documentation varies




NS2 Chronicle

• 1989: REAL by Keshav

• 1995: ns by Floyd, McCanne at LBL

• 1997: ns-2 by the VINT project (Virtual

InterNetwork Testbed at LBL, Xerox PARC, UCB,

12

USC/ISI

• Now: ns-2.35 maintained at USC/ISI• Also there is NS-3, but it has no backwardcompatibility with NS-2.

04-Jul-14 udhayprakash.blogspot.in



NS2 Chronicle

• REAL Simulator →NS (or NS1)→NS2→NS3.

• NS-1

–

– Developed by the network research group at theLawrence

– Berkeley National Laboratory (1989) – Derived from REAL Simulator

– Simulation description language: TCL




NS2 Chronicle

• NS-2 – Object Oriented (OTcl instead of TCL)

– Built in C++ and provides a simulation interface throughOTcl

– Developed by UC Berkeley

– Difficult for the first time users• Very few user friendly manuals. Ex: ns manual

• Needs scripting language, queuing theory and modelling techniques

knowledge• Complaint about inconsistent results

• And BUGS!!!!

• But, large community support




NS3

• No backward compatibility with NS2

• YANS (Yet Another Network Simulator)→NS-3 base

• NS-3.1 (2008), NS-3.11(2011), …

• Built in C++ and python • Good support for LTE and Wimax

• Simple to work with…..and suitable for dumping into andgetting data from real-time devices.

• No support for some protocols which were supported inns-2.

• But, lesser community support




NS-2 Directory Structure

TK8.0 OTcl tclclTcl8.0 ns-2 nam-1

ns-allinone

tcl

ex test lib

...

...

examples validation tests

C++ code

OTcl code

mcast

simple.tcl




NS-2 Environment

SimulationScenario

1 2

set ns_ [new Simulator]

c cr p

C++Implementation

_ _

set node_(1) [$ns_ node]

class MobileNode : public Node

{ friend class PositionHandler; public:

MobileNode();••

}




NS2 Architecture




Why two languages? (Tcl & C++)

• C++: Detailed protocol simulations require systems programming

language

– byte manipulation, packet processing, algorithm implementation

– Run time s eed is im ortant

– Turn around time (run simulation, find bug, fix bug, recompile, re-run) is

slower

• Tcl: Simulation of slightly varying parameters or configurations

– quickly exploring a number of scenarios

– iteration time (change the model and re-run) is more important




What is Tcl/Tk ?•It is a Scripting language to describe a high-level programming language withrelatively transparent syntax

•Tools Command Lanuage (TCL) –simple string based scripting language for controlling and extending applications.

– provides generic programming facilities such as variables, loops, and

rocedures. –Tcl syntax is very much similar to UNIX shell programming.

•Tool k it (TK) – based on X-window system.

– provides facilities (widgets) for building user interfaces.

•Tcl/Tk –Excellent tools for Rapid prototyping.

–Tcl/Tk is interpreted rather than compiled. ( The interpreter is in !/opt/bin/wish )

–weakly typed language (strings and integer variables are interchangeable).




Basic Tcl

variables:

set x 10

puts “x is $x”

functions and expressions:

procedures:

proc pow {x n} {

if {$n == 1} { return $x }

set part [pow x [expr $n-1]] set y [pow x 2]

set y [expr x*x]

control flow:

if {$x > 0} { return $x } else {return [expr -$x] }

while { $x > 0 } {

puts $x

incr x –1

}

re urn expr x par

}

Also lists, associative arrays, etc.

=> can use a real programminglanguage to build networktopologies, traffic models, etc.




Basic oTclClass Person

# constructor:

Person instproc init {age} {

$self instvar age_

set age_ $age

# subclass:

Class Kid -superclass Person

Kid instproc greet {} {

$self instvar age_

puts “$age_ years old kid: What’s}

# method:

Person instproc greet {} {

$self instvar age_

puts “$age_ years old: How areyou doing?”

}

up, u e

}

set a [new Person 45]

set b [new Kid 15]$a greet

$b greet

# “new” in ns2 only

=> can easily make variations of existing things (TCP, TCP/Reno)

Person a 45

Kid b 15

a greet

b greet04-Jul-14 22udhayprakash.blogspot.in

S li Obj M d l



Split Object Model• Split Object Model with shared class hierarchy

– Control (OTcl) vs. Data (C++)

• TclCL provides ‘glue library’ to “easily” share functions, variables, etc

– OTcl into C++: command(), tcl.result()

– C++ into OTcl: tcl.eval()

• Not all classes are mirrored exactly

OTcl C++

23

OTcl script

describing

simulation T c l C L

udhayprakash.blogspot.in



C++ and OTcl Linkage

• Class Tcl: instance of OTcl interpreter

Tcl& tcl = Tcl::instance();

tcl.evalc(“puts stdout hello world”);

tcl.result() and tcl.error()• Class TclObject and TclClass

– Variable bindings

bind(“rtt_”, &t_rtt_)

– Invoking command method in shadow class

$tcp advanceby 10




Calling Otcl functions from C++

• OTcl

Agent/TCP instproc advance {num} {

set window_ [expr $window_ + $num]

return $window_

}

• C++Tcl& tcl = Tcl::instance();

char *result;

tcl.evalf(“%s advance %d”, name_, size);

result = tcl.result();

wnd_ = atoi(result);




EmbeddedTcl

• How it works

– tcl2c++: provided by TclCL, converts tcl scripts

into a C++ static character array

– .tclsh8.0 bin/tcl-expand.tcl tcl/lib/ns-lib.tcl |

tcl2c++ et_ns_lib > gen/ns_tcl.cc




C++ and OTcl Separation

• “data” / control separation – C++ for “data”:

• per packet processing, core of ns

• fast to run, detailed, complete control

– OTcl for control:• Simulation scenario configurations

• Periodic or triggered action

• Manipulating existing C++ objects

• fast to write and change

+ running vs. writing speed

– Learning and debugging (two languages)




Object Granularity Tips

• Functionality

– Per-packet processing C++

– Hooks, frequently changing code OTcl

• a a managemen

– Complex/large data structure C++

– One-time configuration variables OTcl




Ns2 Installation Procedure

• Linux Installation (preferred):

– Go to udhayprakash.blogspot.in

– Search for ns2 installation procedure

– …..

• Windows Installation

– Go to

http://nsnam.isi.edu/nsnam/index.php/Running_Ns _and_Nam_Under_Windows_9x/2000/XP_Using_

Cygwin




Where to find…/ns-2/tcl/lib

• ns-lib.tcl: – The simulator class and most of its member functiondefinitions

• ns-default.tcl: –

• ns-packet.tcl:

– The packet header format initialization implementation

• other OTcl files: – implementation of compound network objects or the front end(control part) of network objects




SESSIO -2

Working with s2orking with s2




A Simple Topology

n0 n1

Application

AgentAgent

0 1

0 0

head_ enqT_ queue_ deqT_ link_ ttl_

drophead_

rcvT_

drpT_

Link

n1 – n0




N1 N2

C l a s s i f i e r

C l a s s i

Agent

Node

Local

C l a s s i f i e

r

C l a s

s i

Agent

Node

Local

Link

Link

i e r

Addr

Porti e r

Addr

Port

Enq Trace Deq Trace Rcv Trace

Drp Trace

Delay TTL

Drop head

Queue




Using ns

Problem

Simulationmodel

Setup/runsimulationwith ns

Resultanalysis

Modifyns




NS-2 Generic Script Structure

set ns [new Simulator]set ns [new Simulator]# [Turn on tracing]# [Turn on tracing]

# [Turn on# [Turn on visualizervisualizer]]

# Create topology# Create topology

# Setup packet loss, link dynamics# Setup packet loss, link dynamics

# Create:# Create:

## -- multicast groupsmulticast groups

## -- protocol agentsprotocol agents

## -- application and/or setup traffic sourcesapplication and/or setup traffic sources

# Post# Post--processingprocessing procsprocs

# Start simulation# Start simulation


h d l i



Event Scheduler Creation

• Event is a packet ID that is unique for a packet, which constitutes:

– Scheduled time

– The pointer to an object that handles the event

• An event scheduler

– Keeps track of simulation time – Fires all the events in the event queue

• Create event scheduler: set ns [new simulator]

• Schedule an event: $ns at <time> <event>

– Event is any legitimate ns/tcl function

– $ns at 5.0 “finish”

• Start scheduler

– $ns run


T i



Tracing


T i



Tracing

• Packet tracing and event tracing – Objects that are inserted between nodes

– Insert from OTcl using trace{} method

• $ns trace-all $file, or

38

• [$ns link $n0 $n1] trace $file

• Monitoring

– Record counters of interest for all packets or on a

per-flow basis

• …or roll your own


T i



Tracing• ns and nam trace file formats

– ns also supports show_tcphdr_ variable controlling display of TCPflags

• ns format

opop tsts prevhopprevhop nexthopnexthop typetype sizesize flagsflags flowidflowid srcsrc dstdst seqnoseqno pktidpktid

39

• Enque [+], dequeue [-], receive [r], drop [d]

• Types are

• Flags are – ECN-CE [E], -ECT [N], -CE [C], -CWR [A]; plus

– priority [P] and TCP fast start [F]

++ .. cpcp –––––––––––– .. ..


Vi li ti ( )



Visualization (nam)

set nf [open out.nam w]$ns namtrace-all $nf

Proc finish {} {

global ns nfclose $nf

exec nam out.nam &

exit 0

}


T l C ti



Topology Creation


S di D t



Sending Data


Sending Data



Sending Data


Creating TCP Connections



Creating TCP Connections

• Create TCP agent and attach it to the node set tcp0 [new Agent/TCP]

$ns attach-agent $n0 $tcp0

• Set null0 [new Agent/TCPSink]

$ns attach-agent $n1 $null0

• Connect the agents $ns connect $tcp0 $null0


Traffic on top of TCP



Traffic on top of TCP

• FTP

– set ftp [new Application/FTP]

– $ftp attach-agent $tcp0

• Telnet

– Set telnet [new Application/Telnet]

– $telnet attach-agent $tcp0


NS2 pre and post processing



NS2 pre- and post processing

• pre-processing: – traffic and topology generators

– NSG 2.1 (for more details, go to udhayprakash.blogspot.in )

– tclTutor

• post-processing:

– simple trace analysis, often in Awk, Perl, or Tcl.

– Awk scripting is preferred.


Summary



Summary

• Simulators help in easy verification of protocols inless time, money.

• NS2 offers support for simulating a variety of

protocols suites and scenarios• Front end is oTCL, back end is C++

• NS2 is on-going effort of research and development.


Reference



Reference

1) ns2 website: http://www.isi.edu/nsnam/ns2) Marc Greis' tutorial

3) Jae Chung tutorial

4) Ns manual

– . .6) Nsnam web pages – http://www.isi.edu/nsnam/

7) NS by example – http://nile.wpi.edu/NS/

8) Tutorial – Marc Greis's tutorial

9) Discrete-event simulation software – http://www.topology.org/soft/sim.html

10) Introduction to NS2(PPT), Prepared by Changyong Jung


ns2 network simulator- tutorial for begineers

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