MM/IP MM/IP MM/IP Various layer 2: PPP, ATM, FR, Packet over Sonet... Figure 3.15 Multimedia over IP combined with mobile and fixed Internet Content provider and other roles Multiple 'virtual' IP networks Service network, Internet, Access Transport corporate network IP host/client IP routing IP host/server Figure 3.16 IP - the network glue Networks and Technologies 3.5 WHAT IS A HORIZONTAL NETWORK? This concept of layered network architecture is already in use in datacom networks, SO it is not brand new. The development within the telecom industry during the last decade has underlined that the future range of successful services is impossible to predict. Bearing this lesson in mind, network architects are highly aware of the need to build the networks as flexible service platforms. The number of services increases quickly, especially because of the paradigm shift when the telecom, datacom and media industries converge. Together with fast technical development, this provides a background to the changing architecture of networks in the telecom world, from what is frequently called the vertical networks of the past and present, to the horizontal networks of the future. The development is supported by operators, service providers, vendors and standardization bodies. A truly horizontal network is built up by autonomous layers. Each layer has its own management, control (if any) and resources. Each layer is built on standards-based components and the interfaces between the layers are also standardized. A layered architecture allows each layer to evolve independently as technology evolves. Multiple service networks can share the same transport network. The horizontal network architecture can provide all types of communication and appli- cation services, only restricted by the capabilities of terminals and the used access. Applications will/should thus be independent of any core/radio technology/fixed access technology. In such a service-converged situation users from GSM, UMTS, PSTN/ISDN, CATV etc. will be able to use t