.. include:: replace.txt Introduction ------------ The |ns3| 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 |ns3|. Primary documentation for the |ns3| project is available in four forms: * `ns-3 Doxygen/Manual `_: Documentation of the public APIs of the simulator * Tutorial (this document) * `Reference Manual `_: Reference Manual * `ns-3 wiki `_ The purpose of this tutorial is to introduce new |ns3| 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 |ns3| 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: * Ns-3 is not an extension of `ns-2 `_; it is a new simulator. The two simulators are both written in C++ but |ns3| 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 |ns3|. The project will continue to maintain ns-2 while |ns3| is being built, and will study transition and integration mechanisms. * |ns3| is open-source, and the project strives to maintain an open environment for researchers to contribute and share their software. For ns-2 Users ************** For those familiar with ns-2, the most visible outward change when moving to |ns3| is the choice of scripting language. Ns-2 is 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 |ns3|, 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 nam, but new animators are under development. Since |ns3| 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 |ns3|). We will try to highlight differences between ns-2 and |ns3| as we proceed in this tutorial. A question that we often hear is "Should I still use ns-2 or move to |ns3|?" The answer is that it depends. |ns3| does not have all of the models that ns-2 currently has, but on the other hand, |ns3| 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 |ns3| (a porting guide is under development). There is active development on multiple fronts for |ns3|. The |ns3| developers believe (and certain early users have proven) that |ns3| is ready for active use, and should be an attractive alternative for users looking to start new simulation projects. Contributing ************ |ns3| 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 |ns3| like they have for ns-2: * Open source licensing based on GNU GPLv2 compatibility; * `wiki `_; * `Contributed Code `_ page, similar to ns-2's popular Contributed Code `page `_; * ``src/contrib`` directory (we will host your contributed code); * Open `bug tracker `_; * |ns3| developers will gladly help potential contributors to get started with the simulator (please contact `one of us `_). 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 |ns3| (e.g. "this tutorial section was not clear..."), reports of stale documentation, etc. are much appreciated. Tutorial Organization ********************* The tutorial assumes that new users might initially follow a path such as the following: * Try to download and build a copy; * Try to run a few sample programs; * Look at simulation output, and try to adjust it. As a result, we have tried to organize the tutorial along the above broad sequences of events.