'Telecommunications traffic' is a phrase used to describe all the variety and complexity of the usage of a network. It is the comings and goings of demand, in response to user behaviour and to the network's reaction. Its detailed specification is a means to an end - merely the first step in the evaluation of the quantities that are meaningful and useful to the network engineer, and therefore the type and complexity of its characterisation reflects the richness of its array of uses. Time-honoured representations of network traffic by pure-chance streams, which have worked well for many years, are now insufficient. The new data networks display a complexity of behaviour which requires a corresponding richness of input, and this has required the development of a multitude of traffic descriptions. These include not only extensions of classical models, such as multi-bit-rate sources, but also such very different areas as the effective bandwidth models now in widespread use for ATM modelling, self-similar or fractal traffics, and the complex self-coupled and adaptive behaviour of TCP/IP traffic streams. This chapter will distinguish loosely between characterisation and modelling. The first of these implies the purely phenomenological description of traffic, i.e. the analysis of measurement data, and the production of high-level statistical descriptions. Modelling, by contrast, covers the detailed low-level production of probabilistic models of traffic that can actually be used to make predictions about network and system behaviour.

Inspec keywords: telecommunication traffic; probability; transport protocols; asynchronous transfer mode

Other keywords: TCP/IP traffic streams; network traffic; telecommunication traffic; ATM modelling; system behaviour; user behaviour; traffic descriptions; network behaviour; network reaction; probabilistic models; multi-bit-rate sources

Subjects: Communication switching