em 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 3.4). Any traffic system is characterized by two main functions: resources and resource control. This is a programmed control, not to be confused with management. In ISDN, the concepts of user plane with the user traffic, and control plane were introduced and Understanding Changing Telecommunications - Building a Successful Telecom Business Management system Traffic system Customer network Customer management management IT & system management Network operation warehousing Service provisioning Transmission Internet ATM/FR PLMN/PSTN/ISDN Figure 3.3 The management and the traffic systems Telecom business Traffic system = Network M = Management system Figure 3.4 The triangle defined. In PSTN the planes are not described separately, and consequently there are no standardized interfaces between them. In the evolving horizontal network, the distinction between these planes is pronounced. An example is the split into a control layer and a connectivity layer. Packet-switched networks (or packet-mode networks) are sometimes regarded as having no control plane. Especially in connectionless networks, the control layer is difficult to identify, since for example routing is done for every single packet. (Connectionless = 'Any packet can theoretically take its own path to the receiving end'.) However, there Networks and Technologies is always a kind of control plane. In packet-switched networks it just partly deals with other issues than the tasks of the control plane of circuit-switched networks. For IP networks this is a heritage from the original US defence-based requirements on robustness, with quite a lot of intelligence located at the te