Network Simulator 2 (ns2)

1. Network Simulator NS2

The purpose of this tutorial is to make it easier for new ns users to use ns and nam, to create their own simulation scenarios for these tools and to eventually add new functionality to ns. We have found the existing documentation to be rather useful for users who already know the basic features of ns, while it can be a bit tedious for new users to extract the necessary information from the manuals and the example scripts.

In this tutorial we will lead you through some simple examples, introducing more and more new features as we go along. The ultimate goal is that after a short time you are able to efficiently use ns and to find any further information you might need in the existing documentation. For this purpose We will also try to tell you where we found the information in this tutorial ourselves, so you not only learn how to use ns, but also how to use its documentation.

1.1. Downloading/ Installing & nam
         You can build ns either from the  various packages (Tcl/Tk, otcl, etc.), or you can download an 'all-in-one' package. We would recommend that you start with the all-in-one package, especially if you're not entirely sure which packages are installed on your system, and where exactly they are installed. The disadvantage of the all-in-one distribution is the size, since it contains some components that you don't need any more after you compiled ns and nam. It's still good for first tests, and you can always switch to the single-package distribution later.

Note: The all-in-one package only works on Unix systems.

You can download the package from the at UCB. If you have any doesn't solve your problem, you might want to ask the ns-users mailing list                                                            After the installation is complete, you should make sure that your path points to the 'ns-allinone/bin' directory (if you installed the ns-allinone package) where links to the ns and nam executables in the 'ns-2' and 'nam-1' directories can be found or (if you built ns and nam from the pieces) let your path point directly to the directories with the ns and nam executables.

On some systems you will also have to make sure that ns can find the library 'libotcl.so'. If you installed the ns-allinone package, it should be in 'ns-allinone/otcl/'.

1.2. Starting ns

You start ns with the command 'ns <tclscript>' (assuming that you are in the directory with the ns executable, or that your path points to that directory), where '<tclscript>' is the name of a Tcl script file which defines the simulation scenario (i.e. the topology and the events). You could also just start ns without any arguments and enter the Tcl commands in the Tcl shell, but that is definitely less comfortable.

Everything else depends on the Tcl script. The script might create some output on stdout, it might write a trace file or it might start nam to visualize the simulation or all of the above. These possibilities will all be discussed in later sections.

2. TCL SCRIPT

In this section, you are going to develop a Tcl script for ns which simulates a simple topology. You are going to learn how to set up nodes and links, how to send data from one node to another, how to monitor a queue and how to start nam from your simulation script to visualize your simulation.

 3. NAM

You can either start nam with the command 'nam <nam-file>' where '<nam-file>' is the name of a nam trace file that was generated by ns, or you can execute it directly out of the Tcl simulation script for the simulation which you want to visualize.  Below you can see a screenshot of a nam window where the most important functions are being explained.

The first Tcl script,In this section, you are going to develop a Tcl script for ns which simulates a simple topology. You are going to learn how to set up nodes and links, how to send data from one node to another, how to monitor a queue and how to start nam from your simulation script to visualize your simulation.