pters. 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 support servers (ASuS - an Ericsson term). Service capability servers interface the network, acting like bridges between the applications and the network resources. Application support servers perform other tasks like security and charging. The OMA service enablers have a much wider scope. OMA service enablers are the ser- vice supporting elements of