scribe occurrence rates of different error or fault events. Typical events are set-up failures, bit error rate and unwanted or unsuccessful connection clearings. It must also be possible for the actors to cooperate in the production of services, by specializing into various niche activities. Obviously this demands clear interfaces within Networks and Technologies Grade of service Trans- mission Frequency Availabi- Dependa- Switching bility Synchro- Service routing nization Numbering O & M Signalling Charging Organi- zation Figure 3.2 A classical map of fundamental technical plans the network. So far we are used to interconnection via vertical interfaces, where two actors meet, for example in a network interconnect point. Now a horizontal interconnect or interworking is becoming more common. Considering the service production aspect it would be natural to start this chapter with a comprehensive section on service requirements. However, the ongoing paradigm shift implies quite a lot of technical changes of the networks, calling for a basic technical chapter in this book, before going into service optimization of the network. In this first network-oriented section we look therefore more at the architectural options of the network rather than on service implementation aspects, which are covered in Chapter 8. 3.2 WHAT IS A NETWORK? 3.2.1 THE FUNCTIONAL CONTENT OF A SERVICE PRODUCTION UNIT To make it simple, let us start with the traditional telecom networks and split them into two logical systems: the traffic system and the management system. The traffic system serves the end-users, and the management system supports the traffic system with the activities that can be found in Figure 3.3. This is a general system model, which is valid for all types of network architectures. The management system is at least partly a function of the traffic system, that is first we have to understand the traffic system before defining how to manage it. Adding the users we get the triangle which is found throughout this book (see Figure 