A crucial issue in the design of software components in a wide network is the ability to support various types of network flow and to guarantee the Quality of Service (QoS) requirements to the users. In particular, we need rigorous but easy-to-use techniques for predicting and analyzing the performance of computer networks. To this purpose, formal modeling techniques can be used for studying network nodes. Petri Net (PN) is a powerful technique to this aim, because of its analytical capability and its possible evolution in time. In this paper, we present PN models (including PN based-model, colored PN, timed PN and stochastic PN) for modeling the characteristics of a switching node in a Wide Area Network (WAN). By using PN in this case study, we demonstrated the possibility of evaluating the performance of any other network nodes as in ATM network or in IP network such as Internet.
