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A Discrete-Event Network Simulator
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Tutorial |
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A Discrete-Event Network Simulator
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Tutorial |
The ns-3 simulator is a discrete-event network simulator targeted primarily for research and educational use. The ns-3 project, started in 2006, is an open-source project developing ns-3.
The purpose of this tutorial is to introduce new 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:
For those familiar with ns-2, the most visible outward change when moving to ns-3 is the choice of scripting language. Programs in ns-2 are scripted in OTcl and results of simulations can be visualized using the Network Animator 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. New animators and visualizers are available and under current 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 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 sometimes be ported to ns-3 (a porting guide is under development). The support available on the user mailing list, and the developer and maintainer activity, is higher for ns-3. A good guideline would be to look at both simulators, and in particular the models available for your research, but when in doubt or when starting new simulation projects, choose the tool that is under more active development (ns-3).
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 ns-3 like they have for ns-2:
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.
The tutorial assumes that new users might initially follow a path such as the following:
As a result, we have tried to organize the tutorial along the above broad sequences of events.