Performance modelling of computer networks

This paper intends to present an overview of the main problems that appear when we wish to estimate the performance of a non existing system or a future situation of an existing system. The main techniques used for representing the workload and the system performance will be also presented. It will start with a definition of the main problems existing in this field, then present the main techniques used for modelling computer networks and their workload and the methods used to obtain solutions from them. Finally a simple example will show the use of all of these techniques and methods.