an attractive service plan, choosing appropriate service layer enablers and 'Economy of service' functions, and finally tuning the FP 'knobs' for best security, quality and cost efficiency. The service-layer enablers and more about FPs will be covered later. As indicated in Figure 8.17 QoS, security and interconnect FPs are covered in separate chapters. Later in this chapter there are separate overviews on the numbering and signalling plans. Some routing features are inherently covered in the MPLS standard. Section 8.10 on traffic cases illustrates 'packet handling control'. Let us now apply a top-down approach. In fact the service layer part should ultimately be independent of the underlying 'find and connect machine'. 8.7 TOP-DOWN APPROACH TO PACKET DESIGN 8.7.1 THE COMPONENTS OF THE WHOLE SYSTEM Figure 8.19 shows one way of segmenting a communication system: content, applica- tion logic, service enablers, adaptations to the bearer technology, and finally the bearer network. The left side represents the terminal device with corresponding functions. Adap- tations are considered part of the QoS plan 8.7.2 THE APPLICATION LOGIC Applications are sometimes called end-user services. The complex terminology relation- ship between applications and services, including application logic, is found in Chapter 1. e-commerce support, data bases Application control Application logic Application logic and support Service enablers MMS, Bluetooth Positioning, MMS, kJava give added value Adaptations Adaptations QoS, security support for content Multi-mode GPRS/ UMTS (and other) networks transport capabilities Terminals Service network & underlying networks Figure 8.19 Segmentation of a communication system Understanding Changing Telecommunications - Building a Successful Telecom Business 8.7.3 SERVICE ENABLERS There are two semantically different service enabler groups. Both are applied in the service network and/or terminals. The original Parlay/OSA service enablers consist of service capability servers (SCS) and application sup