The preface has talked in general terms about modelling concepts and the reasons why models exist. But, as you may know, there are many fields of modelling and this book sets out to introduce you to a selection of communications network modelling disciplines. It has been organised in such a way that each area has its own chapter and, while these can be read individually, the designer should attempt to keep the bigger picture in mind.

The opening chapter describes BT's Utilisator tool and how the outputs have provided solutions not only to network design questions but also to architectural issues.

Chapter 2 moves on to consider a different aspect of network modelling how to design a network that is robust, resilient and survivable. Networks are now an integral part of a company's infrastructure and recent catastrophic events have demonstrated how much a business comes to rely on the resilience of its networks.

This leads us on to the question of capacity (which is considered in Chapter 3) how to design and plan a network that has neither too little nor too much (wasted) capacity, a subject which will be familiar to anyone who has been involved with designing a network.

Until now we have looked at how the network should be planned and designed. We have seen modelling techniques that aid in that process. Let us now turn to a network already deployed the PSTN (public switched telephone network). It has been around for a long...