Tài liệu NS-2 Tutorial pdf

What’s NS-2• Network simulator – Discrete event simulator • It covers multiple layers – Application layer, transport layer, network layer and link layer.. Network Topology: NodeAddr Clas

NS-2 Tutorial

Motivation

What’s NS-2

• Network simulator

– Discrete event simulator

• It covers multiple layers

– Application layer, transport layer, network layer and link layer

• Supports the simulation of

– intserv/diffserv, Multicast, Transport,

Applications, Wireless (fixed, mobile, satellite)

• Packet level

Model world as events

– simulator has list of events ordered by simulation time– process: take next one, run it, until done

– each event happens in an instant of virtual (simulated) time, but takes an arbitrary amount of real time

NS uses simple model: single thread of control =>

no locking or race conditions to worry about (very

easy)

Discrete Event Simulation

History and Status

• REAL variant (1989)DARPA (LBL, Xerox PARC, UCB, and USC/ISI) (1995)

• Currently; DARPA; NSF; collaboration with researchers: ACIRI, UCB Daedelus, CMU, Sun Microsystems, NORTEL, Cisco

ns-2 Programming Languages

• NS-2 is an object oriented simulator, written in C++,

with an OTcl (Object Tool Command Language)

interpreter as a front-end

• Back-end C++

– Defining new agents, protocols and framework.

– Manipulations at the byte/bit levels.

– if you have to change the behaviour of an existing C++ class in

ways that weren't anticipated

• Front-end Otcl Topologies, scenarios, simulations, …

– Script language (easy topology modifications)

– if you can do what you want by manipulating existing C++

Why Two Languages

• Simulator had two distinct requirements

– Detailed simulation of Protocol(Run-time speed)

– Varying parameters or configuration(Change model &

rerun)

• C++ is fast to run but slower to change

• Otcl runs much slower but can be changed

quickly

OTcl and C++: The Duality

Pure C++

objects

Pure OTcl objects

C++/OTcl split objects Split Object:

Object created in Otcl has a corresponding object in C++.

Network Topology: Node

Addr Classifier

Port Classifier

Multicast Classifier

multiclassifier_

Network Topology: Link

duplex link

Routing

Addr Classifier

Port Classifier

dmux_

entry_

0 1

Addr Classifier

Port Classifier

classifier_

dmux_ entry_

1 0 Link n0-n1

Link n1-n0

0 1

Addr

Classifier

Port Classifier

classifier_

dmux_

entry_

0 Agent/TCPagents_

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

1 0

Link n0-n1

Link n1-n0

0 Agent/TCPSin

k agents_

Application: Traffic Generator

0 1

Addr

Classifier

Port Classifier

classifier_

dmux_

entry_

0 Agent/TCPagents_

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

1 0

Link n0-n1

Link n1-n0

0 Agent/TCPSinkagents_

Application/FTP

Plumbing: Packet Flow

0 1

Addr Classifier

Port Classifier

entry_

0 Agent/TCP ClassifierAddr

Port Classifier

entry_

1 0

Running NS-2 Program

• http://www.isi.edu/nsnam/ns

• Tcl (Tool Command Language)

– http://dev.scriptics.com/scripting

• OTcl (MIT Object Tcl)

– ~otcl/doc/tutorial.html (in distribution)

• ns manual

– Included in distribution: ~ns/doc

– documentation.html

Basic Syntax

Tcl commands are evaluated in two steps:

First the Tcl interpreter parses the commands into words, performing

substitution along the way.

Tcl Basics

• Basic syntax

– command arg1 arg2 arg3 …

– command is either the name of a built-in command

First example: hello world!

• Hello world!

– puts stdout {Hello World!}

• Two points to emphasize

– Arguments are interpreted by the command

– Curly braces are used to group words together into a single argument

Variable Substitution

• Variable substitution

– i: the character ‘i’

– $i: the variable i

– set v1 6

– set v2 $v1 (variable substitution)

• Grouping: group words (argument) together into one

argument

• Grouping with curly braces

– Curly braces prevent substitution in the group

• Grouping with double quotes

– Double quotes allow substitution to occur in the group

• Example:

• => The length of hello is 5

• =>The length of $a is [string length $a]

set d [expr [expr $a - $b] * $c]

for {set k 0} {$k < 10} {incr k} {

OTcl Basics

• Creating a class

• Defining instance procedures

– class_name instproc proc_name {args} {… }

• Defining instance variables

OTcl Basics

• Creating an instance

– set new_inst [ new class_name]

• Calling an instance procedure

– $new_inst proc_name {args}

• Using an instance value

– $new_inst set v1 10

– set v2 [$new_inst set v1]

Class Mom

Mom instproc greet {} {

$self instvar age_

puts “$age_ years old

mom: How are you doing?”

}

Class Kid -superclass Mom

Kid instproc greet {} {

$self instvar age_

puts “$age_ years old

kid: What’s up, dude?”

}

set mom [new Mom]

$mom set age_ 45 set kid [new Kid]

$kid set age_ 15

$mom greet

$kid greet

45 years old mom: How are you doing?

15 years old kid:

What's up, dude?

• NS2, and all of it's peer programs &

dependencies are installed in/usr/ns/ on the

Fedora machines in the Main Undergraduate Lab

in Math Sciences It is also available on the

compute servers csc, csd, and cse Some notes:

• (1) You *must* put /usr/ns/otcl-1.9 and

/usr/ns/lib into your LD_LIBRARY_PATH

environment variable.

– If you are using csh or tcsh, you can set it like:

setenv LD_LIBRARY_PATH

/usr/ns/otcl-1.9:/usr/ns/lib

– If you are using sh or bash, you can set it like: export LD_LIBRARY_PATH=/usr/ns/otcl-1.9:/usr/ns/lib

• (2) You *must* put /usr/ns/tcl8.4.5/library into your TCL_LIBRARY environment variable

Otherwise ns/nam will complain during startup.

– If you are using csh or tcsh, you can set it like:

setenv TCL_LIBRARY /usr/ns/tcl8.4.5/library

– If you are using sh or bash, you can set it like: export TCL_LIBRARY=/usr/ns/tcl8.4.5/library

• (3)You *should* put /usr/ns/bin into your PATH environment variable Otherwise you will have

to type the full path to ns/nam when you want

to run them.

– If you are using csh or tcsh, you can set it like:

setenv PATH /usr/ns/bin:$PATH

– If you are using sh or bash, you can set it like: export PATH=/usr/ns/bin:$PATH

Elements of ns-2 Simulation

• Step 1: Create the event scheduler

• Step 2: Turn on tracing

• Step 3:Create network topology

• Step 4: Create transport connection

• Step 5: Create traffic on top of transport connection

Topology

Step 1: Creating Event Scheduler

• Create event scheduler

– set ns [new Simulator]

Step 2: Tracing

• Trace packets on all links

– $ns trace-all [open test.out w]

<event> <time> <from> <to> <pkt> <size> <fid> <src> <dst> <seq> <attr>

+ 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

• Trace packets on all links in nam format

– $ns namtrace-all [open test.nam w]

• Must appear immediately after creating scheduler

Step 3: Creating Network

• Nodes

– set n0 [$ns node]

– set n1 [$ns node]

• Links and queuing

– $ns duplex-link $n0 $n1 <bandwidth> <delay>

<queue_type>

– <queue_type>: DropTail, RED, CBQ, FQ, SFQ, DRR

#Create 6 nodes

for {set i 0} {$i < 6} {incr i} {

set n($i) [$ns node]

Step 4: Creat transport conneciton

TCP

• TCP

#Create a TCP agent and attach it to node n(0)

#set up connection between node 0 and node 3set src_tcp [new Agent/TCP/Reno]

$ns attach-agent $n(0) $src_tcp

set dst_tcp [new Agent/TCPSink/DelAck]

$ns attach-agent $n(3) $dst_tcp

$ns connect $src_tcp $dst_tcp

Step 4: Creat transport conneciton

UDP

• UDP

# UDP flow between n1 and n7

set src_udp [new Agent/UDP]

Step 5: Creating Traffic (On Top of UDP)

• CBR

#Setup a CBR over UDP connection

set cbr [new Application/Traffic/CBR]

$cbr attach-agent $src_udp

$cbr set type_ CBR

$cbr set packetSize_ 512

$cbr set rate_ 0.8Mb

Creating Traffic: (On Top of TCP)

• FTP

set ftp [new Application/FTP]

$ftp attach-agent $src_tcp

$ftp set packetSize_ 512

Things to Remember

• Topology, agents, sources, start

• Connect the agents

– Slot not found error

• Start/Stop the sources

• In procedures, declare global variables before use

• “$ns run” – last line