Mobile IP tutorial

- summary or tutorial about Mobile IP and its applications for mobility within fixed line and cellular telecommunications.

Mobile IP is becoming increasingly important. Mobile IP is required because high speed data and mobility are two key factors for today's wireless and telecommunications industry.

While high speed data is one issue, mobility is equally important. People need to take laptop computers with them use them anywhere as if they were working from their home network. While it is possible to make connections reasonably easily, improvements are being put in place to ensure full mobility and ease of use. Accordingly Mobile IP is a key element enabling this facility to become more robust and easier to use

As infrastructures and standards are already in place for data transfer it is necessary to adapt them to take account of mobility and introduce Mobile IP via an existing route rather than introducing completely new techniques. The most common services are the data services using the Internet Protocol (IP). When using this, a user which may be any form of node or computer is normally connected to a particular network or sub-network. Moving the computer from one network or sub-network to another creates problems because routing tables need to be updated to enable the data to reach the user at the new location.


Home operation

When connected to the base network, users are attached to their home network and all the routing tables needed to send the data to the required destination are set up for the computer in this locations. Using their home network IP address they can move anywhere within this particular network with no problem.


Mobile IP foreign agent and foreign networks

It is becoming increasingly common for computers to need to operate in networks other than their home network. The mobility of laptops has made this increasingly common. The network it connects to will not be its home network, but instead it will be what is termed a foreign network. Under these circumstances it needs a method of connecting back to the home network so that data packets sent to the home network can be forwarded to the new location and vice versa.

Mobile IP achieves this using what is called a Foreign Agent (FA). Each network has its own foreign agent to enable mobile data operation to be provided. It operates by advertising its presence and services on its network looking for any foreign users that may have attached to its network. Once a foreign user is found it communicates with them to establish the required information to link to the home network.

Similarly on the home network there is an equivalent agent and this is naturally called the "Home Agent" (HA). This Home Agent acts as what is termed a "proxy" for the mobile user. In other words it takes the place of the home IP location and routes data to the foreign agent, allowing communication with what is termed the "correspondent node" (CN).

In operation the foreign agent connects to the home agent when authentication is done and it uses what is termed an IP tunnel for communication. In this tunnel IP packets are packed within IP packets communicating the data. In this way the computer is able to move around freely using this Mobile IP, and communicate with data packets being routed via the home network.


Cell phone applications

With more data being transmitted over cellular networks there is a similar need for mobility within this arena as well, and accordingly mobile networks are also starting to employ Mobile IP. Work is well advanced on the CDMA2000 system used widely in North America, Asia and a number of other parts of the world. For UMTS, other areas of development are receiving the main focus of development and Mobile IP work is expected to follow on and be included in later releases of the standard.

The way in which IP is used on a cellular system is very similar to that employed using a dial up phone connection where a computer is to connect to the Internet. Here the user makes a connection using what is termed the Point to Point Protocol (PPP). As the connection is established the service provider assigns an IP address to the user. Once this has occurred then the data packets have an address to which they can be routed. While the connection is maintained all packets of data are routed to this IP address and others are obviously sourced from it.

The same happens when a mobile phone connects to the internet. A connection is established and an IP address is assigned to the phone or laptop. This works well while the phone is connected to the same base station or local switching centre. However when it needs to move away, a problem arises because each switching centre acts as a different sub-network. As when a mobile moves from one switching centre to the next the connection needs to be broken and a new one established using a new IP address. For CDMA2000 networks this is known as Simple IP. This is clearly not an efficient method of operating and considerably reduces the performance of the system because it breaks all the IP based connections made by applications running on the mobile node.

Accordingly the mobile phone system is treated as a network in the same way as it is for a wired LAN. Accordingly each switching centre has a foreign agent. This operates in the same way that it does for a wired LAN system. It communicates messages from a mobile operating that has moved away from its home switching centre, and in this way the IP connection is not broken.

By adopting this approach the foreign agents serving different switching centres are used, and the information updated with the home agent as the mobile moves from one switching centre to the next. Although this complicates the handover process, it enables a continuous connection to be maintained, despite the mobile moving its location and requiring to be served by different switching centres.


Summary

With the telecommunications scene changing rapidly, moving from a voice centred service to a data centred service and hybrid approaches being offered to provide the optimum service, Mobile IP is an important technique to be used to enable seamless transition from one area to the next, and one technology to the next.

By Ian Poole


Read more telecommunications standards & protocols tutorials . . .

Erlang basics IMS Mobile IP SIP

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