Earlier chapters introduced the basic concepts and theories embodied in analytical modeling. Addressed were basic concepts in queuing systems theory, its application to computer systems modeling, and an introduction to network modeling. This chapter will address the use of analytical and simulation models specifically from the viewpoint of use as performance evaluation tools.

15.1 Introduction

In the past several years, the use of analytical performance models instead of the more widely used and familiar methods has become increasingly popular because of their relative simplicity of implementation and robustness of applications. These analytical models have been successful in estimation of such performance measures as throughputs, average queue lengths, and mean response times for a real system. This chapter is an introduction to queuing techniques for the modeling of computer communication networks, not an in-depth study.

The use of modeling to describe and imitate a real system has been with us since the beginning of the information revolution. These models are used not only to measure the performance of existing systems but also as part of the design and development of new systems. This latter goal is best attained through the use of analytical queuing models, as we will see in the following discussion of methods of performance evaluation.

The major performance evaluation tools (see Figure 15.1) other than queuing models are rules of thumb, linear projection, simulation, and benchmarking. These methods are listed in order of increasing complexity and implementation difficulty. The rules of thumb have been defined by the observation...