IP Mobility and Location Acquisition

IP mobility is a feature that is prevalent in networks that permit easy mobility, like wireless LANs. IP mobility provides a mobile device the option of retaining its original IP address. As the device moves, it acquires new IP addresses, but packets addressed to the original address are routed to the new address by a router in the original network. IP mobility presents similar problems to that generated by the Virtual Private Network (VPN) for the acquisition of location information. Figure 7.11 shows how a typical IP mobility solution might be used.

Figure 7.11: IP mobility allows changes in an IP address by tunneling messages.

In IP mobility, a router in the initial, or "Home," network forwards messages to the device at its new IP address. This means that sessions established using the original IP address can be maintained, even though the IP address of the device changes as it moves. A forwarding address is provided to the router in the Home network when it changes. The forwarding address can either point to the device or a similar router in the current, or "Visited," network. The host sending the mobile device data does not need to be aware that the device is moving.

The link between the original network and the mobile device is analogous to the tunnel that is established for a VPN. Just as with a VPN, the mobile device needs to be aware that it cannot contact the LIS in its home network. The device needs to be aware that it needs to contact the LIS in the network that provides physical network access and use the IP address that it has acquired from the same local access network.