A General Purpose Network Simulation Tool

This paper presents NESSY (NEtwork Simulation SYstem): a whole environment for performance evaluation of communication networks. The modeling methodology proposed by NESSY is mainly based upon the OO (ObjectOriented) techniques and the FDT (Formal Description Technique). With OO approach the network model is a collection of objects. FDT is used to describe the objects that model the network components. These objects are elementary models named ESO (Elementary Simulation Object). These two techniques are used separately through two phases: the modeling phase, where ESOs of a given domain of communication networks are written, and the building phase, where the complete model is built with instances of ESO. The main feature of ESO is to be reusable in different studies. The description of ESO is done according to ECFSM (Extended Communicating Finite State Machine) and with the dedicated LASSY modeling language. This language is derived from the ESTELLE FDT. During the building phase, the model is build by modular and hierarchical composition. The simulation model is not a compiled program but a run-time program. So, full flexibility and interactivity are achieved to control the simulation and to tune the network model.