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@c PART:  Introduction

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@c The below chapters are under the major heading "Introduction"

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@c Introduction

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@node Introduction

@chapter Introduction

@menu

* For ns-2 Users::

* Contributing::

* Tutorial Organization::

@end menu

The @command{ns-3} simulator is a discrete-event network simulator targeted 

primarily for research and educational use.  The 

@uref{http://www.nsnam.org,,ns-3 project}, 

started in 2006, is an open-source project developing ns-3.

Primary documentation for the @command{ns-3} project is available in four

forms:

@itemize @bullet

@item @uref{http://www.nsnam.org/doxygen/index.html,,ns-3 Doxygen/Manual}:  

Documentation of the public APIs of the simulator

@item Tutorial (this document)

@item @uref{http://www.nsnam.org/docs/manual.html,,Reference Manual}:  Reference Manual

@item @uref{http://www.nsnam.org/wiki/index.php,, ns-3 wiki}

@end itemize

The purpose of this tutorial is to introduce new @command{ns-3} users to the 

system in a structured way.  It is sometimes difficult for new users to

glean essential information from detailed manuals and to convert this

information into working simulations.  In this tutorial, we will build 

several example simulations, introducing and explaining key concepts and

features as we go.

As the tutorial unfolds, we will introduce the full ns-3 documentation 

and provide pointers to source code for those interested in delving deeper

into the workings of the system.

A few key points are worth noting at the onset:

@itemize @bullet

@item Ns-3 is not an extension of @uref{http://www.isi.edu/nsnam/ns,,ns-2}; 

it is a new simulator.  The two simulators are both written in C++ but 

@command{ns-3} is a new simulator that does not support the ns-2 APIs.  Some 

models from ns-2 have already been ported from ns-2 to ns-3. The project will

continue to maintain ns-2 while ns-3 is being built, and will study transition

and integration mechanisms.

@item @command{Ns-3} is open-source, and the project strives to maintain an 

open  environment for researchers to contribute and share their software.  

@end itemize

@node For ns-2 Users

@section For ns-2 Users

For those familiar with ns-2, the most visible outward change when moving to 

ns-3 is the choice of scripting language.  Ns-2 is 

scripted in OTcl and results of simulations can be visualized using the 

Network Animator @command{nam}.  It is not possible to run a simulation

in ns-2 purely from C++ (i.e., as a main() program without any OTcl).

Moreover, some components of ns-2 are written in C++ and others in OTcl.

In ns-3, the simulator is written entirely in C++, with optional

Python bindings.  Simulation scripts can therefore be written in C++

or in Python.  The results of some simulations can be visualized by

@command{nam}, but new animators are under development.  Since ns-3

generates pcap packet trace files, other utilities can be used to

analyze traces as well.

In this tutorial, we will first concentrate on scripting 

directly in C++ and interpreting results via ascii trace files.  

But there are similarities as well (both, for example, are based on C++ 

objects, and some code from ns-2 has already been ported to ns-3).

We will try to highlight differences between ns-2 and ns-3

as we proceed in this tutorial.

A question that we often hear is "Should I still use ns-2 or move to

ns-3?"  The answer is that it depends.  ns-3 does not have all of the

models that ns-2 currently has, but on the other hand, ns-3 does have

new capabilities (such as handling multiple interfaces on nodes 

correctly, use of IP addressing and more alignment with Internet

protocols and designs, more detailed 802.11 models, etc.).  ns-2

models can usually be ported to ns-3 (a porting guide is under

development).  There is active development on multiple fronts for ns-3.

The ns-3 developers believe (and certain early users have proven) that

ns-3 is ready for active use, and should be an attractive alternative

for users looking to start new simulation projects.  

@node Contributing

@section Contributing

@cindex contributing

@command{Ns-3} is a research and educational simulator, by and for the 

research community.  It will rely on the ongoing contributions of the 

community to develop new models, debug or maintain existing ones, and share 

results.  There are a few policies that we hope will encourage people to 

contribute to @command{ns-3} like they have for ns-2:

@itemize @bullet

@item Open source licensing based on GNU GPLv2 compatibility;

@item @uref{http://www.nsnam.org/wiki/index.php,,wiki};

@item @uref{http://www.nsnam.org/wiki/index.php/Contributed_Code,,Contributed Code} page, similar to ns-2's popular 

@uref{http://nsnam.isi.edu/nsnam/index.php/Contributed_Code,,Contributed Code} 

page;

@item @code{src/contrib} directory (we will host your contributed code);

@item Open @uref{http://www.nsnam.org/bugzilla,,bug tracker};

@item @command{Ns-3} developers will gladly help potential contributors to get

started with the simulator (please contact @uref{http://www.nsnam.org/people.html,,one of us}).

@end itemize  

We realize that if you are reading this document, contributing back to 

the project is probably not your foremost concern at this point, but

we want you to be aware that contributing is in the spirit of the project and

that even the act of dropping us a note about your early experience 

with ns-3 (e.g. "this tutorial section was not clear..."), 

reports of stale documentation, etc. are much appreciated. 

@node Tutorial Organization

@section Tutorial Organization

The tutorial assumes that new users might initially follow a path such as the

following:

@itemize @bullet

@item Try to download and build a copy;

@item Try to run a few sample programs;

@item Look at simulation output, and try to adjust it.

@end itemize

As a result, we have tried to organize the tutorial along the above

broad sequences of events.

@c ========================================================================

@c Resources

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@node Resources

@chapter Resources

@menu

* The Web::

* Mercurial::

* Waf::

* Development Environment::

* Socket Programming::

@end menu

@node The Web

@section The Web

@cindex www.nsnam.org

@cindex documentation

@cindex architecture

There are several important resources of which any @command{ns-3} user must be

aware.  The main web site is located at @uref{http://www.nsnam.org} and 

provides access to basic information about the ns-3 system.  Detailed 

documentation is available through the main web site at

@uref{http://www.nsnam.org/documents.html}.  You can also find documents 

relating to the system architecture from this page.

There is a Wiki that complements the main ns-3 web site which you will find at 

@uref{http://www.nsnam.org/wiki/}.  You will find user and developer FAQs 

there, as well as troubleshooting guides, third-party contributed code, 

papers, etc. 

@cindex mercurial repository

@cindex ns-3-dev repository

@cindex release repository

The source code may be found and browsed at @uref{http://code.nsnam.org/}. 

There you will find the current development tree in the repository named

@code{ns-3-dev}. Past releases and experimental repositories of the core

developers may also be found there.

@node Mercurial

@section Mercurial

Complex software systems need some way to manage the organization and 

changes to the underlying code and documentation.  There are many ways to

perform this feat, and you may have heard of some of the systems that are

currently used to do this.  The Concurrent Version System (CVS) is probably

the most well known.

@cindex software configuration management

@cindex Mercurial

The @command{ns-3} project uses Mercurial as its source code management system.

Although you do not need to know much about Mercurial in order to complete

this tutorial, we recommend becoming familiar with Mercurial and using it 

to access the source code.  Mercurial has a web site at 

@uref{http://www.selenic.com/mercurial/},

from which you can get binary or source releases of this Software

Configuration Management (SCM) system.  Selenic (the developer of Mercurial)

also provides a tutorial at 

@uref{http://www.selenic.com/mercurial/wiki/index.cgi/Tutorial/},

and a QuickStart guide at

@uref{http://www.selenic.com/mercurial/wiki/index.cgi/QuickStart/}.

You can also find vital information about using Mercurial and @command{ns-3}

on the main @command{ns-3} web site.

@node Waf

@section Waf

@cindex Waf

@cindex make

@cindex build

Once you have source code downloaded to your local system, you will need 

to compile that source to produce usable programs.  Just as in the case of

source code management, there are many tools available to perform this 

function.  Probably the most will known of these tools is @code{make}.  Along

with being the most well known, @code{make} is probably the most difficult to

use in a very large and highly configurable system.  Because of this, many

alternatives have been developed.  Recently these systems have been developed

using the Python language.

The build system @code{Waf} is used on the @command{ns-3} project.  It is one 

of the new generation of Python-based build systems.  You will not need to 

understand any Python to build the existing ns-3 system, and will 

only have to understand a tiny and intuitively obvious subset of Python in 

order to extend the system in most cases.

For those interested in the gory details of Waf, the main web site can be 

found at @uref{http://freehackers.org/~tnagy/waf.html}.

@node Development Environment

@section Development Environment

@cindex C++

knowledge of C++ and object-oriented concepts is assumed in this document.

We will take some time to review some of the more advanced concepts or 

possibly unfamiliar language features, idioms and design patterns as they 

appear.  We don't want this tutorial to devolve into a C++ tutorial, though,

so we do expect a basic command of the language.  There are an almost 

unimaginable number of sources of information on C++ available on the web or

in print.

If you are new to C++, you may want to find a tutorial- or cookbook-based

book or web site and work through at least the basic features of the language

@cindex toolchain

@cindex GNU

software toolchain is the set of programming tools available in the given 

environment. For a quick review of what is included in the GNU toolchain see,

@cindex Linux

Typically an @command{ns-3} author will work in Linux or a Linux-like

environment.  For those running under Windows, there do exist environments 

which simulate the Linux environment to various degrees.  The @command{ns-3} 

It can, however, sometimes be problematic due to the way it actually does its 

emulation, and sometimes interactions with other Windows software can cause 

problems.

@cindex Cygwin

@cindex MinGW

If you do use Cygwin or MinGW; and use Logitech products, we will save you

quite a bit of heartburn right off the bat and encourage you to take a look

at the @uref{http://www.mingw.org/MinGWiki/index.php/FAQ,,MinGW FAQ}.

@cindex Logitech

Search for ``Logitech'' and read the FAQ entry, ``why does make often 

crash creating a sh.exe.stackdump file when I try to compile my source code.''

Believe it or not, the @code{Logitech Process Monitor} insinuates itself into

every DLL in the system when it is running.  It can cause your Cygwin or

MinGW DLLs to die in mysterious ways and often prevents debuggers from 

@node Socket Programming

@section Socket Programming

@cindex sockets

We will assume a basic facility with the Berkeley Sockets API in the examples

used in this tutorial.  If you are new to sockets, we recommend reviewing the

API and some common usage cases.  For a good overview of programming TCP/IP

sockets we recommend @uref{http://www.elsevier.com/wps/product/cws_home/680765,,Practical TCP/IP Sockets in C, Donahoo and Calvert}.

There is an associated web site that includes source for the examples in the

book, which you can find at:

@uref{http://cs.baylor.edu/~donahoo/practical/CSockets/}.

If you understand the first four chapters of the book (or for those who do

not have access to a copy of the book, the echo clients and servers shown in 

the website above) you will be in good shape to understand the tutorial.

There is a similar book on Multicast Sockets,

@uref{http://www.elsevier.com/wps/product/cws_home/700736,,Multicast Sockets, Makofske and Almeroth}.

that covers material you may need to understand if you look at the multicast 

examples in the distribution.