ese principles can be built into a generic logical network structure, see Fig. 3.91. This structure can also be seen as an evolution from the ISDN logical net- work structure in Fig. 3.90. Network Application Systems Network operator Teleservice System Teleservice Process Control Centralized services Service Distributed services process control process control management Connection Fixed Connection management Process Control Mobility Process {RA,RM,AT,SWC} Mobility Control management Signalling Support Signalling Systems (LAPD, CCS, etc.) management Teleservice Connection Resource Resource System System Transport CSP Transport (PDH, SDH, etc.) management Connectivity System Logical Network Management System Fig. 3.91 The generic logical network structure The model is generic in the sense that it is applicable to any type of communica- tion system. So far, no network concept has exactly this logical network structure; however, this is not what the model claims. The model shows instead the direction in which the telecom and datacom industries are going. The model represents a number of trends that started with narrowband ISDN in the mid-1980s (the intro- duction of the user and control plane, CCS, etc.), and now has its technical prereq- uisites in low-cost transmission systems (based on optical fibre technology), on ATM and IP technologies and on emerging mobile technologies (as EDGE and WCDMA²1 for broadband packet-oriented mobile services (like GPRS). The generic model indicates two major trends: 3 Logical Network Modelling 1. Networks will (and have already, to some extent) evolve to comprise four major logical systems: a system for management of logical networks (the Logical Net- work Management System in Fig. 3.91), a system that provides connectivity for everything (the Connectivity system), a system that provides teleservices (the Teleservice System), and systems that are network applications (Network Appli- cation Systems). In present literature, the last three components are sometimes referred to as the c