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Handoff in mobile and wireless networks Wireless data services use small-coverage high-bandwidth data networks such as IEEE whenever they are available and switch to an overlay service such as the General Packet Radio Service (GPRS) network with low bandwidth when the coverage of a Wireless Local Area Network (WLAN) is not available. From the service point of view, Asynchronous Transfer Mode (ATM) combines both the data and multimedia information into the wired networks while scaling well from backbones to the customer premises networks | Mobile Telecommunications Protocols For Data Networks. Anna Hac Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-85056-6 10 Handoff in mobile and wireless networks Wireless data services use small-coverage high-bandwidth data networks such as IEEE whenever they are available and switch to an overlay service such as the General Packet Radio Service GPRS network with low bandwidth when the coverage of a Wireless Local Area Network WLAN is not available. From the service point of view Asynchronous Transfer Mode ATM combines both the data and multimedia information into the wired networks while scaling well from backbones to the customer premises networks. In Wireless ATM WATM networks end user devices are connected to switches via wired or wireless channels. The switch is responsible for establishing connections with the fixed infrastructure network component either through a wired or a wireless channel. A mobile end user establishes a Virtual Circuit VC to communicate with another end user either mobile or ATM end user . When the mobile end user moves from one Access Point AP to another AP a handoff is required. To minimize the interruption of cell transport an efficient switching of the active VCs from the old data path to the new data path is needed. Also the switching should be fast enough to make the new VCs available to the mobile users. When the handoff occurs the current QoS may not be supported by the new data path. In this case a negotiation is required to set up new QoS. Since a mobile user may be in the access range of several APs it will select the AP that provides the best QoS. During the handoff an old path is released and then a new path is established. For the mobility feature of a mobile ATM routing of signaling is slightly different from that of the wired ATM network. First mapping of Mobile Terminal MT routing identifiers to paths in the network is necessary. Also rerouting is needed to reestablish connection when the mobiles move around. It .