1.1 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 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 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.

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