TABLE OF CONTENTS Performance modelling is the abstraction of a real system into a simplified representation to enable the prediction of performance. It can, however, mean different things to people working in different domains. The basic principles are, in fact, the same, but the people working within each domain have developed these basic principles to best fit their domain's problem space. The two main domains in telecommunications are network performance and IT systems performance. This chapter will focus on performance modelling in the IT systems domain.
Changes in technology, such as third party software, cheap computing hardware, and a movement towards scalable client/server architectures, will neither prevent nor solve performance problems. On the contrary, integration of in-house and off-the-shelf software and the rapid turnaround of development and integration of systems to hit narrow market windows only serve to increase the risk of poor performance. If a system's data and processing become more distributed, then so does its performance risk. The performance of third party software is reduced by its necessarily generic and flexible nature. Rapid developments, using sophisticated development environments that autogenerate code, also create an increased performance risk. All of these risks have to be managed and minimised, making performance engineering, and, more specifically, performance prediction using modelling techniques, an extremely important option for the modern project manager. Performance modelling gives the following benefits:
relatively inexpensive prediction of future performance;
design support allowing objective choices to be made;
decision support for the future of existing systems;
a clearer...
