ed to and from a central network, as illustrated in Figure 13.22, only a limited number of base stations can be associated with a mobile station at any time. This is further restricted by the fact that a central network controller is connected to a limited number of base stations, and at times inter-network handover is not readily possible. The smaller the cell size, the more frequently a mobile station crosses boundaries from one cell to another. This can result in handover failure, and dropped packets. Broadband Telecommunications Technologies and Management Network Backhaul Finally, network design must also take the availability of backhaul network into account. The transport mechanism for network backhaul varies from technology to technology. In older 1G, 2G and 3G systems, asynchronous transfer mode (ATM) devices were used to connect base stations to their radio network controller and to other network nodes. Connection to the public telephone network was also on ATM devices. Latest 3G standards use internet for backhaul packet transport, because of their lower cost and the scalability of internet protocol (IP) switches. Moreover, 4G standards are designed to operate on an end-to-end IP system where all traffic is packet switched. The backhaul traffic travels mostly over fibre networks. Very- high-bit-rate DSL (VDSL) and cable connections are other options, and where all these are not available, fixed wireless links are used. Next Generation Networks The broadband packet-switched telecommunications system of 3G and 4G standards can be categorised as Next Generation Networks (NGNs), and philosophically follow the vision of the International Telecommunications Union as: a packet-based network able to provide telecommunication services and able to make use of multiple broadband, QoS-enabled transport technologies and in which service-related functions are independent from underlying transport-related technologies. It enables unfettered access for users to networks and to competing service providers and/or servic