Mobile IP for Wireless Devices

[Prasanth]

The convergence of three technology paradigms, viz. light-weight portable computers, the spread of wireless networks and services, and the ubiquitous Internet, aimed at allowing users the freedom to connect to the Internet at any time and in any place, to read email, query databases, retrieve information from the web or to entertain themselves, makes mobile computing a very promising prospect as well as a very formidable challenge. This paper details the mechanism of operation of Mobile IP network protocol, designed and developed to enable efficient and effective communication between a mobile host and a remote server. The paper then also looks at the efficiency versus effectiveness trade-off, the issues of network security against malicious masqueraders and other areas of current research interest.


A mobile node is assigned to a particular network known as its home network. Its IP address on that network, known as its home address, is static. When the mobile node moves its attachment point to another network, that is considered a foreign network for this host. When the mobile node is reattached, it makes its presence known by registering with a network node, typically a router, on the foreign network known as a foreign agent. The mobile node then communicates with a similar agent on the user’s home network, known as home agent, giving the home agent the care-of address of the mobile node ; the care-of address identifies the foreign agent’s location. Generally, one or more routers implement the roles of both home and foreign agents.

The exchange of IP datagrams between such a mobile node ,let us say A, and a sever S, takes place as the following sequence of events :

• Server S transmits an IP datagram destined for mobile node A, with A’s home address in the IP header.The IP datagram is routed to A’s home netowrk.

• At the home network, the incoming IP datagram is intercepted by the home agent.
The home agent encapsulates the entire datagram inside a new IP datagram, which has the A’s care-of address in the header, and retransmits the datagram. The use of an outer IP datagram with a different destination IP address is known as tunneling.

• The foreign agent strips off the outer IP header, encapsulates the original IP datagram in a network-level Protocol Data Unit (PDU) (for example, a LAN Logical Link Control [LLC] frame), and delivers the original datagram to A across the foreign network.

• When A sends IP traffic to S, it uses S’s IP address. In this example, this is a fixed address; that is, S is not a mobile node. Each IP datagram is sent by A to a router on the foreign network for routing to S.

• The IP datagram from A to S travels directly across the Internet to S using X’s IP address.

To support these operations, Mobile IP includes three basic capabilities – Discovery, Registration and Tunneling.