th each other, making it difficult for a user to roam from one radio system to another. To date, no wireless technology has emerged as a long-term universal solution for it. With IP being a Fourth Generation Mobile Networks 2G/2G+ Content Servers Service Content All-IP Servers Creation network Wireless Content Servers Broadband Figure 5.6 All-IP based network model common network layer protocol, an IP based mobile device (with multiple radio interfaces) could roam between different wireless systems. There needs to be a convergence of the core networking infrastructure on the IP protocol suite and a serious effort has been made to replace the IPv4 deployed throughout the Internet by IPv6, which simplifies the mobility support. This is important because then instead of having only one technology available there will be different technologies to assist mobility from one place to another with varying data rates. New Network Model The new model should be flexible enough for a user to be able to access its services independently of its locations, in a transparent way. The user terminal must be able to pick the 'best' available access technology at its current location and use it seamlessly for the provision of the desired services. This homogeneous, high speed, secure, multiservice, multioperator network concept is required to support multiple types of services, from simple network access to complex multimedia virtual reality, and including traditional telecommunication services such as telephony in mobile environments. A type of network is therefore required that must be able to associate service agreements to network control constrains, to monitor this usage per service and user and to provide these services while the user moves (with its terminal changing access technologies). An example of an all-IP based network model is shown in Figure 5.6. The most important point in this context is the development of a quality of service (QoS) architecture for 4G networks, which should be able to support 'any' type of user serv