ABSTRACT
As it can be seen in Figure 5.1, from a simplied user perspective, NS is an object-oriented Tcl script interpreter (OTcl) that has an event timer for simulation, network object libraries, and network initialization libraries. In other words, in order to use NS, a program must be written in the OTcl scripting language. In order to set up and run a network simulation, the user must write an OTcl script that sets an event timer, denes network topology by using network objects and corresponding library functions, and instructs trafc sources when to start and stop packet transmission through the event timer. If the user wants to create a new network object, this can be accomplished by writing an altogether new object or by building a composite one using the existing object library.
