Mobile IP
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.
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 clearly going to
become an increasingly important technique to be used to enable seamless
transition from one area to the next, and one technology to the next.
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