Mobile IPv6

Mobile IPv6
Today’s versions of Internet protocols assume implicitly that any node always has the same point of
attachment to the Internet. Mobile IPv6 allows a host to leave its home subnet while transparently
maintaining all of its current connections and remaining reachable by the rest of the Internet. Already,
there are third-generation cellular phones that are packet-switched instead of circuit-switched, offering
IP services, and the number of mobile Internet devices will continue to rise [505].
The current state of IPv4 architecture does not adequately serve the contemporary Internet in terms
of security, mobility, extensibility, and dynamic reconfigurability. IPv6 is the proposed solution to
these problems, and offers a larger IP address space and a number of fundamental features to enable
wireless networking and mobility. IPv6 is designed to provide sufficient IP addresses for a multitude
of mobile nodes to be deployed in a mobile network, without extensive software additions to keep
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the nodes in communication, and without the security vulnerabilities that lurk in every new layer
of additional networking software. Mobility is built into the IPv6 protocol: a mobile IPv6 node can
use mobility protocols wherever it can get ordinary IPv6 service. The mobile IPv6 protocol does not
require or even define foreign agents, leading to scalable Internet-wide mobility management.
In addition, route optimization signaling enables a mobile IPv6 node to inform its correspondent
node when it acquires a new care-of address. This allows both the mobile node and the correspondent
node to send and receive packets using the shortest path between the two. One useful by-product of
this feature is location-based services. The mobile IPv6 location update signaling can be used by a
correspondent node to infer the geographic location of a mobile node, and hence provide customized
service or content. This optional protocol signaling can be turned off if the mobile node’s location
privacy is an issue [504].
The term “binding” refers to the association of a mobile node’s home address with its care-of
address. When a new message is sent in IPv6, it carries with it the IPv6 Destination Options – additional
information that only the destination node needs to examine. There are four Destination Options available:
Binding Update, Binding Acknowledgement, Binding Request, and Home Address. A mobile node
uses the Binding Update option to inform its HA and its correspondent nodes about its current care-of
address. A Binding Acknowledgement acknowledges a Binding Update. A Binding Request asks a
mobile node to send a Binding Update. The Home Address option is sent by a mobile node to convey
its home address to another node.
IPv6 nodes maintain a Binding Cache, where they store the bindings for other nodes. Information
from Binding Updates is sent to the Binding Cache, and when a node sends a packet, the cache
is searched for an entry containing the destination node’s care-of address. A node also maintains a
Binding Update List containing information about every Binding Update that it has sent to its home
agent and all correspondent nodes. In addition, nodes that serve as HAs maintain a HAs List where
they keep track of information about all of the other HAs on their subnet.
A routing anomaly can occur with IPv6, called triangle routing: when a correspondent node
wants to send a message to a mobile node, the message is routed to the mobile node’s HA, and
from there to the mobile node itself. However, when the mobile node wants to send a message to its
correspondent node, the message is routed directly from the mobile node to the correspondent node.
In fact, mobile nodes set the source address of their transmissions to their care-of address, and utilize
the Home Address Destination Option in such transmissions.
To avoid triangle routing (and optimize routing), mobile nodes must send Binding Updates to any
(mobile or stationary) correspondent node they communicate with. The correspondent nodes cache
the current care-of address, and send messages directly to the mobile nodes on their list.
Route optimization is an integral feature of the IPv6, rather than an additional functionality as
in the IPv4. In addition, the IPv6 does not need to rely on foreign agents (in foreign subnets) to
configure the care-of addresses of mobile nodes – IPv6 uses a neighbor discovery mechanism and
address auto-configuration to handle this task [505].
Implementation of the Mobile IPv6 in 2 and 3G mobile networks primarily requires user plane
(application layer) IPv6 support from the network, installing a HA router in the home network, and the
use of mobile terminals supporting Mobile IPv6 and implementing IP Security (IPSec) infrastructure,
because Mobile IPv6 uses IPSec for all its security requirements.
Mobile IPv6 allows for efficient roaming from a visited network to home network services and
seamless roaming between different access technologies (WLAN, Bluetooth, etc.) using one address
for a mobile node. In addition, mobile nodes can run peer-to-peer services directly without explicit
support from their home network [506].
The number of wireless computing devices (such as mobile phones, laptops, and palmtops) in
use on the Internet reached one billion sometime in 2005. The huge address space of IPv6 will
meet the addressing requirements of the rapidly developing Internet. Since real-time applications like
VoIP in mobile networks depend on smooth handoffs when mobile nodes transition between network
links, a system of buffering packets during transition has been proposed to minimize packet loss. In addition, the IPv6 introduces a packet option called QoS Object that can trigger QoS procedures
when QoS-sensitive applications are in use [503].