onnectivity layer, the communication control layer and the contents and application layer (it is hard to get rid of popular concepts like the "layer"). A trend towards what is sometimes called horizontal integration, thereby indi- cating that the networks of the past and the present are "vertically integrated". The generic model in Fig. 3.91 shows a clear separation between different logi- cal networks, interconnected not by protocols (which represent distribution of functions), but by network service interfaces (which represent service special- ization). This is a prerequisite for implementing logical networks in physical networks of their own, which can also be operated by specialized network oper- ators. In PSTN and ISDN, physical nodes integrate functions from all or several logical networks. If logical networks become implemented as separate physical networks, the physical nodes of these networks can be expected to be considera- bly less complex than their PSTN and ISDN equivalencies. This is what is meant by horizontal integration. A consequence of the trend towards horizontal integration of physical networks that standardization of network service interfaces becomes increasingly impor- tant. In the past, standardization has focused greatly on protocols that implement distribution of functions. Such protocols reflect, to a high degree, peer relations between parties, i.e. both parties provide services to each other-they are equal part- ners. In the networks of the future, we will have a number of additional protocols that represent service specialization, and therefore, to a high degree, reflect client- server (or in SM&AML: user-provider) relations between parties, i.e. only one of the parties provides services. The distinction between peer and user-provider relations cannot easily be described in a message protocol, which is why the abstract protocol becomes an increasingly important modelling concept. It is therefore important that protocol EDGE, Enhanced Data Rate for Global Evolution, is a new radio tr