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Mobile IP Overview, History and Motivation
(Page 3 of 4)
A Better Solution: Mobile IP
The solution to these difficulties
was to define a new protocol especially to support mobile devices, which
adds to the original Internet Protocol. This protocol, called IP
Mobility Support for IPv4, was first defined in RFC 2002, updated
in RFC 3220, and is now described in RFC 3344. The formal name as given
in that document title is rather long; the technology is more commonly
called Mobile IP both in the RFC itself and by networking people.
To ensure its success, Mobile IP's
designers had to meet a number of important goals. The resulting protocol
has these key attributes and features:
- Seamless Device Mobility Using Existing Device
Address: Mobile devices can change their physical network attachment
method and location while continuing to use their existing IP address.
- No New Addressing or Routing Requirements:
The overall scheme for addressing and routing as in regular IP is maintained.
IP addresses are still assigned in the conventional way, by the owner
of each device. No new routing requirements are placed on the internetwork,
such as host-specific routes.
- Interoperability: Mobile IP devices can
still send to and receive from existing IP devices that do not know
how Mobile IP works, and vice-versa.
- Layer Transparency: The changes made by
Mobile IP are confined to the network layer. Transport layer and higher
layer protocols and applications are able to function as in regular
IPv4, and existing connections can even be maintained across a move.
- Limited Hardware Changes: Changes are
required to the software in the mobile device, as well as to routers
used directly by the mobile device. Other devices, however, do not need
changes, including routers between the ones on the home and visited
- Scalability: Mobile IP allows a device
to change from any network to any other, and supports this for an arbitrary
number of devices. The scope of the connection change can be global;
you could detach a notebook from an office in London and move it to
Australia or Brazil, for example, and it will work the same as if you
took it to the office next door.
- Security: Mobile IP works by redirecting
messages, and includes authentication procedures to prevent an unauthorized
device from causing problems.
Mobile IP accomplishes these goals
by implementing a forwarding system for mobile devices. When
a mobile unit is on its home network, it functions normally.
When it moves to a different network, datagrams are sent from its home
network to its new location. This allows normal hosts and routers that
don't know about Mobile IP to continue to operate as if the mobile device
had not moved. Special support services are required to implement Mobile
IP, to allow activities such as letting a mobile device determine where
it is, telling the home network where to forward messages and more.
I explore Mobile IP operation more in the
next topic, and the implementation specifics
in the rest of this section.
Key Concept: Mobile IP solves the problems associated with devices that change network locations, by setting up a system where datagrams sent to the mobile nodes home location are forwarded to it wherever it may be located. It is particularly useful for wireless devices but can be used for any device that moves between networks periodically.
Mobile IP is often associated with
wireless networks, since devices using WLAN technology can move so easily
from one network to another. However, it wasn't designed specifically
for wireless. It can be equally useful for moving from an Ethernet network
in one building to a network in another building, city or country. Mobile
IP can be of great benefit in numerous applications, including traveling
salespeople, consultants who visit client sites, administrators that
walk around a campus troubleshooting problems, and much more.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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