exchanges were not simplified. On the contrary, since the IN concept adds new signalling in the network, the overall interface complexity grew. Managing an IN network has also offered more problems than expected. It should be borne in mind that the IN services to a large extent are 'network ori- ented', often meaning advanced routing, advanced charging or advanced numbering. Such services have little or no content to offer, as opposed to for example WWW ser- vices. A more system-oriented approach was necessary when the mobile telephony systems were standardized. Here the functionality was more distributed, with many 'servers' in the network (such as HLR, VLR, EIR, AUC in GSM) starting with the second gen- eration of systems from the beginning of the 1990s. IN was also introduced in this generation of mobile systems. A mixed fixed-mobile system came with 'fixed cellular systems'. The data-oriented networks, on the other hand, were layered from start, which enables a smooth transition to the new horizontal network. However, except for ATM, they are optimized for data only. The introduction of TCP/IP networks meant something new, especially a possibility for global communication, since IP could 'surf' on other networks. The service offerings on top of TCP/IP, headed by WWW services and e-mail, were another strong feature. So it is not curious that the future network might lend many features from TCP/IP networks. See Figure 3.8. Networks and Technologies Everything Games Voice e-commerce Streaming video Frame relay Ethernet Anything Figure 3.8 The 'secret' behind Internet success and its world-wide connectivity ATM was designed to become a multimedia-capable type of network. ATM has mainly found its niche in the network backbones as an important layer 2 technology. Closer to the subscribers Ethernet is a very strong candidate at layer 2. 3.4 THE CONVERGENCE (OR COLLISION?) 3.4.1 TRANSITION FEATURE 1: CONVERGENCE The previous books in this series ended by describing a number of vertical networks, almost all of them de