This chapter presents the fundamental notions of quality of service (QoS), and the attached performance parameters, for telecommunication networks and equipment. These notions sustain all the activity in performance evaluation of telecommunications systems. Actually, the network provider intends to offer, through a set of equipments, communication services with a quality level corresponding to the expectations of the customers. These objectives are expressed by means of quality of service parameters, and translated into performance parameters of the network elements, more generally defined by international standards, or specified in invitations to tender issued by network providers to manufacturers.

The ability, for equipment, systems and networks architectures to conform to these parameters and their evaluation, are the concern of this book and of the tools that are presented in the following chapters. The presentation of the concepts and of the related parameters is based upon the standards in use, briefly summarized in this chapter. However, the notions we intend to develop are of a generic nature, formulated in different ways in different standards but without any fundamental change because they are not strictly linked to the technology of the day, so that we need only make references to typical definitions from a significant set of standards.

2.1. Standardization organisms and norms

Across the whole sector of telecommunications, standards have a prominent position. The term "standard" stresses perfectly the need of these universal agreements, as their goal is to provide "standard" interfaces allowing heterogeneous components, provided by different manufacturers,...