Mobile IP ( Internet Protocol )

("http://www.ent.ohiou.edu/~sangal/mobileip.html")
Rahul Sangal E-mail: sangal@bobcat.ent.ohiou.edu

1 Introduction to Mobile Computing.
2 The Internet.
3 Mobile Internet.
4 How does Internet Work ?
5 Problem with IP in Mobile Networks.
6 How does Mobile IP work ?
7 Summary
8 References

1. Introduction to Mobile Computing

Due to advances in the wireless communication technology there is a growing demand for providing continuos network access to the user of a portable computer, regardless of their location. Existing network protocols are designed with the assumption of static network topology. Since the invention of computer, we have been witnessing major shifts in computing paradigm almost every decade. Mobile Computing is expected to be next major paradigm in the evolution of computing. Technological advances of 90's are bringing about two major changes that have the potential to reshape the existing network computing into what is known as Mobile Computing. First, portable computers which are powerful as some desktop workstations in terms of computing power, memory, display, and disk storage are beginning to appear. With the availability of wireless network interface s, users of laptop computers are no longer required to remain confined within the wired LAN premises to get the network access. Mobile personal computing devices are becoming ubiquitous as their prices drop and their capabilities increase. With the growing dependence of day to day computing on a distributed information base, providing network attachment to these devices is an essential requirement.

2. The Internet

From its origin as a US government research project, the Internet has grown to become a major component of the global worldwide network infrastructure, linking over 100,000 networks, 50,000 domains, millions of machines, and tens of millions of users around the world. Internet is expanding at a rate normally associated with nuclear chain reaction. Over 130 countries have full TCP/IP Internet connectivity. With the introduction of WWW ( World Wide Web ), an architectural framework for accessing linked documents spread over thousands of machines all over the Internet, it has become a part of daily life.

3. Mobile Internet

Many users on the Internet have portable computers and want to stay connected to the Internet when they visit a distant site away from their homes, office or even while travelling on the road. Using wireless network interfaces, mobile devices can be connected to the Internet in the same way as desktop machines are connected using ethernet, token ring or point to point links. The use of a wireless channel for data communication is not a new development. In fact the wireless technology has been in use over satellite, microwave and cordless channels for over half a century. What is new is its application for providing local and wide area Personal Communication Services.

4. How does Internet work ?

Internet is built upon a collection of networks that cover the world. These networks contains differnt types of computers, and somehow, something must hold the whole thing togather. That something is TCP/IP. TCP/IP is the common name of over 100 protocols that are used to connect computers and networks. The actual name TCP/IP comes from TCP ( Transmission Control Protocol) and IP ( Internet Protocol ). Within Internet data is broken into small packets called fragments. For example, say that you send a long mail on the other side of the country. TCP will divide the message int o packets. Each packet is marked with a sequence number. Each host on the Internet is assigned a unique 32-bit (For IP version 4) IP address. Data are carried out in the form of packets which contain source and destination IP addresses. Internet routers maintain a view of the network topology in the form of routing tables. These tables are consulted when making a packet routing decisions. The process of routing involves inspecting the destinati on address contained in the packet and based on the contents of the routing table, determining the next hop router to which the packet should be relay ed. Each router along the source and the destination nodes repeat this process until the packet is finally delievered to the destination host.

5. Problem with IP in Mobile Network

Under the current addressing scheme the routers all over the world only need to maintain the network portion of the IP address. Which means that Internet address is only meaningful as long as the host using it remains connected to that network denoted by network-ID of that address. In case of Mobile host, when it moves to a new network, leaving its home network, it must be allocate d a new address which is derived from the address space of the new network. Which means the packet for the mobile host will continue to be routed to its home LAN ( or the router ). The owner will no longer get e-mail. and so on. Now we can summarize what kind of solution we are looking for :
a) Each mobile host must be able to use its home IP address anywhere.
b) Changes to the router software and tables is not advisable.

6. How does Mobile IP work ?

We consider a networking envoirnment, which consists of base stations connecte d to the wired network. Base stations and mobile computers are equipped with wireless transmitters and recievers which enable them to communicate with each other. The Base station is the router that connects the mobile host to the rest of the Internet. At any point of time a mobile host is reachable via a Base station. Mobile Hosts owned by a organization should be assigned a permanent IP address within the network number of that organization. The mobile host will use this IP address whether they are connected to the home network or currently attached to some foreign network. Each organization with mobile hosts is responsible for providing a location server on its netwo rk that maintains a database of current location of each of its mobile hosts for which this is a home network. The location of the mobile host is represent ed as the IP address to the Base station on the foreign network to which the mobile host is currently connected. IP packets are routed to the mobile host by delievering them over to its local network to the connected mobile host. The Base station maintains a list of recording the IP address of each visiting mobile host currently connected to the network.
When a mobile host moves to a new Base station, it must notify its new base station, its old base station and its location server on the home network. At the location server, the notifications of a mobile host's movemen t are used to maintain a database of the current location of the mobile host, giving the IP address of the current Base station for each mobile host. When sending an IP packet to a mobile host, the sender need not know that the host is mobile. The packet is sent and routed exactly the same way as and other IP packet, and thus reaches the home network of the mobile host. If the mobile host is currently connected to its home network, the packet is delievered there directly to the host. If, instead the mobile host is currently not connected to its home network, the packet is intercepted by the Location server. The Location server forwards the packet to the mobile host through the base station currently recorded in its database. In this manner packets are recieved by the mobile hosts keeping their home IP address intact.

7. Summary

The kind of solution we talked about in the above section is more specific to Cellular networks designed to support Mobile Personal Communication. Another major shift in the Mobile Personal Communication Networks will be the introduction of communication services via LEO personal communication satellit e systems, which may require different routing mechanisms for the mobile hosts. Although a lot of research is going on to solve the Mobile IP problem employing minimum overhead, the solution described in section 6 is universally accepted as a standard way to achieve the goal of seamless IP routing.

8. References :

1) Proceedings of the IEEE, September 1994.
2) Computer Networks, Third Edition, Andrew S. Tenenbaum.
3) Internet : Complete Reference, Osborne Publications.
4) Mobile Networking Systems based on IP, Thesis, Parvin Bhagwat, Rytgers University.
5) Ubiquitous Mobile Host Internetworking, David B. Johnson, Proceeding of fourth workshop on Workstation Operating Systems, IEEE Computer Society, October 1993.