Lesson 1: Introduction

The researches carried out recently in many research centres indicate the necessity of determining methods of analytical modelling of traffic phenomena occurring in B-ISDN networks (Broadband Integrated Services Digital Network). As a result of the rapid growth in the capacity of transmission links caused by the increasing requirements of modern bandwidth-consuming multimedia applications, the elaboration of time-effective methods of analysis and designing of switching networks has become crucial. However, determining traffic characteristics of multi-service multi-stage switching systems is a complex problem. Basic problems associated with description of such systems, from the traffic theory viewpoint, come from the necessity of servicing various types of traffic sources by the network [COST92COST96]. In principle, the classification of traffic sources in a broadband network is reduced to distinguishing the CBR (Constant Bit Rate) sources and the VBR (Variable Bit Rate) sources. The CBR sources have the defined values of emission rate, while the VBR sources require a greater number of parameters to describe the emitted streams.

To define loads introduced into networks by the VBR sources, the so-called equivalent bandwidth for particular classes of traffic streams generated by the sources is determined [COST92COST96]. The assignment of several constant bit rates to the VBR sources enables the evaluation of traffic characteristics of switching systems in the B-ISDN network by means of multi-rate models worked out for the multi-rate circuit switching [COST92COST96Robe83Fitz91Reim94].

According to these trends, to describe B-ISDN switching groups and nodes, models of the so-called full-availability group carrying a mixture of different multi-rate traffic streams are used, or models of the so-called limited-availability group carrying such streams are employed. This is the reason why the links models in multi-rate systems are the subject of the tutorial.