1. Mobile IP support requires a Mobile Node in each mobile device and a Home Agent in each such device’s Home Network. Foreign Agents may be present in the network the device is visiting. When a mobile device visits a different network, IP datagrams destined for the device are intercepted by its Home.
2. When a mobile device visits another network, IP datagrams destined for the device are intercepted by its Home Agent and tunneled to the visited network using a temporary IP address. If there is a Foreign Agent on the visited network, it receives the tunneled packets, unpacks them and forwards them to the Mobile Node, which passes to the mobile phone; or the mobile node receives them first. Finally, the Mobile Node reinserts the original datagrams into the stack, resulting in a transparent operation using only the original IP addresses.
-In a cellular telephone network, handoff is the transition for any given user of signal transmission from one base station to a geographically adjacent base station as the user moves around. In an ideal cellular telephone network, each end user's telephone set or modem (thesubscriber's hardware) is always within range of a base station. The region coveredby each base station is known as its cell. The size and shape of each cell in anetwork depends on the nature of the terrain in the region, the number of base stations,and the transmit/receive range of each base station. In theory, the cells in anetwork overlap; for much of the time, a subscriber's hardware is within range of morethan one base station. The network must decide, from moment to moment, which basestation will handle the signals to and from each and every subscriber's hardware.
Each time a mobile or portable cellular subscriber passes from one cellinto another, the network automatically switches coverage responsibility from one basestation to another. Each base-station transition, as well as the switching processor sequence itself, is called handoff. In a properly functioning network, handoffoccurs smoothly, without gaps in communications and without confusion about which basestation should be dealing with the subscriber.