With the great expansion of the Internet in the past few years, many new service providers and venders of networking equipment evolved to compete against one another. This melting pot has called for a comprehensive, universal and practical approach to the performance evaluation of devices running the most widely used technologies and applications. In this paper we address testing methodologies considering in most cases an Asynchronous Transfer Mode (ATM) device and a network of such devices. The proposed methodologies addresses network performance and characterization based on gained industrial practical experience from two perspectives: the service providers and vendors of switching/routing equipment. These procedures although mostly specific to ATM can be easily generalized to other technologies.