Download Microsoft PowerPoint Presentation: 11_1_MobileComputing

Mobile and Wireless Computing
Lecture 11: Introduction to Mobile IP
We will discuss :
 The basic framework in mobile IP
 The concepts of foreign network, home network
and correspondent nodes
 Mobility binding and security issues
 Changes in IPv6 and future of mobile IP
This lecture is based on a tutorial on Mobile IP by,
Charles E. Perkins
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Why do we need Mobile IP?

At present, any access to the internet has an
inherent restriction of point of attachment.

We go to office, university or workplace and
access the internet from a fixed IP address. This
IP address may be for a desktop or laptop
computer.
If we take our computer to a different place,
outside our usual network, we have to
reconfigure it with a new IP address.

Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Why do we need Mobile IP?



It will be very nice if mobility does not affect
internet sessions.
For example, we should be able to take a laptop
computer from our workplace to home without
noticing any change in the internet connectivity.
In general, users should be able to move around
seamlessly. Mobility of the computer should be
completely transparent to the applications
running on the computer.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Why do we need mobile IP?

For example, the user should continue to
receive emails and keep connected to the
internet.

Mobile IP makes mobility completely transparent
to applications running on a mobile computer.

The applications feel that the mobile computer is
connected to its usual IP address even if it is far
away from its home network.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Comparison with telephones

A good comparison can be made with mobile
telephone networks.

A user can move around and continue using a
mobile phone without noticing any change in
connectivity.

A fixed IP address is similar to a fixed home
telephone connection. You can only
communicate if you are at home.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Comparison with telephones

On the other hand mobile phones have given
users complete freedom of communication.
Users can communicate anytime and anywhere.

Users need not worry about their location and
movement and connections are made in a
completely transparent fashion.

However access to internet is not as transparent
when users are mobile.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Difference between internet access and telephone

However, there is a clear difference between
internet access and mobile telephones.

Users typically run applications that require
resources from their home network. An example
is emails. Users receive emails at their email
address even though they are moving.
Hence there is a need to maintain connections
with the user’s home network.

Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
The problem with Internet Protocol (IP)

IP routes packets to their destinations according
to IP addresses.

An IP address is associated with a fixed network
location.

When a user moves, each new point of
attachment has a new IP address. Hence it is
very difficult to keep mobility transparent.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
How IP works

Routing tables are used for routing packets.

The routing tables maintain the next hop
information for each destination IP address.
A packet is forwarded from the incoming network
interface to the outgoing interface according to
the next hop information.
Hence, an IP address contains the information
about the point of attachment of a computer.


Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
How TCP works

Most internet connections use TCP. A good
example is email clients.

A TCP connection is uniquely identified by four
components :
<IP_source, port_source,IP_dest, port_dest>

If we change any one of these four components,
the connection will be broken.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
How TCP works

If a packet has to be delivered to a mobile
node’s current point of attachment, we need to
change the destination IP address and port
number.

It is impossible to do so once a connection has
been established.

Mobile IP allows a mobile node to use two
different IP addresses.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Home address and Care-of address



The home address is static and effectively
identifies the user to the internet. TCP
connections are established using the home
address.
The mobile node gets a new care-of address
every time it connects to a new point of
attachment.
The home address is associated with the home
network and the care-of address is associated
with a foreign network.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Foreign Network and Foreign Agent

When a mobile node moves, it first connects to a
foreign agent in a foreign network.

Next, the mobile node is assigned a care-of
address (an IP address) by the foreign network.

The node now registers its care-of address with
the home agent.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Home Network and Home Agent



The home network contains a network node
called Home Agent. The home address of the
mobile node is the IP address of the home
agent.
The home agent is responsible for receiving all
the packets sent to the mobile node when the
mobile node is away.
It is the responsibility of the home agent to
deliver the packets to the mobile node at its
current point of attachment.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Correspondent Node



A correspondent node is a computer that sends
packets to the mobile node. A correspondent
node is typically connected to its own home
network.
A correspondent node is aware of only the IP
address of the mobile node in the home network
of the mobile node.
Any packet from the correspondent node is
delivered to the home agent.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
A Schematic Diagram of Mobile IP
Mobile
node
Foreign agent
Correspondent
Node
Home agent
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
The Basic Mechanisms in Mobile IP

1.
2.
3.
The correct functioning of mobile IP depends
upon the coordination of three different
activities
Discovering the care-of address of a mobile
node.
Registering the care-of address with the home
agent.
Tunneling of packets from the home agent to
the care-of address.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Discovering the care-of Address


1.
2.
In mobile IP, both a foreign agent and a home
agent periodically broadcast agent
advertisement messages.
The role of foreign and home agents have been
kept similar for two reasons :
A home agent for one mobile node may act as
a foreign agent for another mobile node.
A mobile node can decide whether it is in the
home network or in a foreign network.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Agent Advertisements
Hence, an agent advertisement has the functions :
 It allows mobile nodes to discover foreign agents
and get care-of addresses.
 It allows the mobile node to know the services
provided by the foreign agent.
 It allows the mobile node to determine whether
an agent is its home agent or a foreign agent.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Solicitation from a Mobile Node



A mobile node can generate agent solicitation
messages when it is looking for a foreign
agent.
It may happen that a foreign agent has offered
service, but the mobile node can no longer
receive advertisements from the foreign agent.
The mobile node assumes that the foreign
agent is out of range. It may contact other
foreign agents whose advertisements it has
received, or it may send solicitation messages.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Registering the Care-of Address

When a mobile node receives a care-of address
from a foreign agent, its home agent needs to be
informed.

Image from the tutorial by Charles Perkins
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Registering the Care-of Address



The mobile node sends a registration request to
its home agent through the foreign agent who
has provided the new care-of address.
When the home agent receives the request, it
updates its routing table and sends a registration
reply back to the foreign agent.
The mobile node starts receiving packets from
its home agent once the home agent has
accepted its registration request.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Binding for a Mobile Node




The home agent associates the care-of address
of the mobile node with its home address.
Any packet coming to the home agent will be
tunneled to the mobile node in future.
The home agent also associates a registration
lifetime for the mobile agent.
The three entities : home address, care-of
address and registration lifetime is called a
binding for the mobile node.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Authentication of a Registration Request




It is extremely important to authenticate a
registration request. Otherwise, a malicious
node may send fake registration requests.
Each mobile node and home agent must create
digital signatures that cannot be forged.
This is done by using a one-way hash algorithm
over all the data in the registration request.
However, there is still a possibility of a replay
attack.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Prevention of Replay Attack


A malicious node may replay a valid registration
request later.
It may be possible that the mobile node has now
a new foreign agent and the home agent has no
way to distinguish between a valid registration
request and the replay of an old registration
request.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Prevention of Replay Attack



Each new registration request must contain
unique data so that two separate registrations
will not have the same hash.
Each registration message has a special
identification field that changes with each new
registration message.
One possibility is to use a time stamp for
identification as the time from the mobile node
changes with each registration message.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Prevention of Replay Attack



However, there is a problem with using time
stamps. The mobile node and the home agent
may differ in their clocks more and more.
A better strategy is to use a random number for
identification every time a new registration
request is sent.
The chance that two 32-bit random numbers will
be the same is very low.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Delivery of Packets to the Mobile Node

When the home agent receives a packet for the
mobile node, it delivers the packet to the care-of
address of the mobile node.

The home agent applies a transformation on the
packet so that the care-of address becomes the
destination address.
A reverse transformation is applied when the
packet arrives at the care-of address. It appears
as if the mobile node’s home address is the
destination address.

Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Tunneling and IP-within-IP

Image from the tutorial by Charles Perkins
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Tunneling and IP within IP



The transfer of the packet from the home agent
to the care-of address is called tunneling.
The home agent is the source of the tunnel. The
home agent inserts a new tunnel header in front
of the IP header of a packet addressed to the
mobile agent and received by the home agent.
The tunnel header is the care-of IP address of
the mobile node. The old header is preserved as
it was in the original packet.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Tunneling and IP within IP




The foreign agent is the receiver of the tunnel.
When the foreign agent receives the tunneled
packet, it has to delete the tunnel header to
recover the original packet.
The foreign agent delivers the packet to the
mobile node after removing the tunnel header.
Hence, for the mobile node, the packet looks like
a normal packet exactly similar to a packet that
it receives when it is connected to the home
network.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Communication with Correspondent Nodes
Mobile
node
Foreign agent
Correspondent
Node
Home agent
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Communication with Correspondent Nodes




The communication between the mobile node
and a correspondent node is asymmetrical.
Once the mobile node knows the IP address of
the correspondent node, it can send packets
directly to the correspondent node.
However, the correspondent node cannot send
packets directly to the care-of address of the
mobile node.
The correspondent node has to send packets to
the home agent.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Changes in Mobile IPv6




IPv6 has many features for mobility that are not
present in IPv4.
Most importantly, there is no need of a foreign
agent for supporting mobility in IPv6.
A mobile node will be able to configure its own
care-of address through stateless address
autoconfiguration and neighbour discovery.
This will reduce latency and increase security in
Mobile IPv6.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Changes in Mobile IPv6



The tunneling mechanism for delivering packets
from the home agent to the mobile node will
remain similar. In particular, the details of IPv6within-IPv6 has been already worked out.
However, one of the main changes in IPv6 will
be route optimization.
When a correspondent node knows the current
care-of address of a mobile node, it can send
packets to the mobile node directly.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
Communication with Correspondent Nodes in IPv6
Mobile
node
Correspondent
Node
Home agent
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
Mobile and Wireless Computing
End of the course
I hope you enjoyed the course.
Thank You
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)