The route does not have to be the same in both directions. Therefore, a mobile host needs to have a stable IP address in order to be uniquely identifiable to other Internet hosts. However, when a mobile host moves from one network to another, as shown in Fig. 1, the IP address of an MH will change due to the enforced hierarchical address structure of the Internet. If the MH has only standard IP stack in its operating system, the TCP connection will break up following this movement. (Mondal, 2003)
Mobile IP (Perkins, 2002) is the standard proposed by IETF to offer seamless mobile computing. Mobile IP extends IP by allowing a mobile computer to utilize two IP addresses: one for identification, and another for routing. For example, it enables a TCP connection to keep alive and re-route packets when the mobile host moves between points of attachment.
Mobile Host (MH): A host or router that changes its point of attachment from one network or sub network to another, without changing its IP address. A mobile node can continue to communicate with other Internet nodes at any location using its (constant) IP address.
In order to route data packets after MH has moved into its new location, MIP also defines simple mechanisms to deliver packets to the mobile node when it is away from its home network. ...
Foreign Agent (FA): A router on a mobile node's visited network that cooperates with the home agent to complete the delivery of packets to the mobile node while it is away from home.
Home Address: A long-term IP address for MH on its home network.
Care of Address (CoA): Address for MH that reflects its current point of attachment when it is away from its home network.
In order to route data packets after MH has moved into its new location, MIP also defines simple mechanisms to deliver packets to the mobile node when it is away from its home network. Following each change of point of attachment, MH registers with HA with its new CoA. When HA receives IP packets for MH, it will encapsulate the packets with MH's CoA as the destination address and forward them to FA. FA will decapsulate the packets by strip off the outer IP header and deliver the packets to MH.
IP mobility support for IPv4 is specified in RFC3344. The Mobile IP protocols support transparency above the IP layer, including maintenance of active TCP connections and UDP port bindings. It allows a node to continue using its 'permanent' home address no matter where the node physically attached to. Therefore, ongoing network connections to the node can be maintained even as the mobile host is moving around the Internet. (Mondal, 2003)
Mobile IP defines three functional entities where its mobility protocols must be implemented: Mobile Node (MN), Home Agent(HA) and Foreign Agent(FA). Figure 2 shows the three functional entities and routing of datagrams transmitted from a MN away from home. When a MN moves, it finds an agent on its local network by the Agent Discovery process. It listens for Agent