Mobile IPv6

Without support for mobility in IPv6, packets cannot reach the destination Mobile Node while it is away from the home network. In order to continue communicating, a Mobile Node could change its IP address from time to time while moving to a foreign network, but it would not be possible to maintain transport and higher-layer connections.

Mobility support in IPv6 is increasing in importance, as mobile devices are gradually

dominating the network access device market originally belonged to PCs and in the near future, they are likely to account for the majority of Internet access machines. From the concept of last section, we can know that Mobile IPv6 allows a Mobile Node to move from one network to another without changing the Mobile Node's IP address and keep Mobile Node always addressable by its Home Address (An IP address assigned to the MN within its home subnet prefix on its home link).

Packets may be routed to the MN (Mobile Node) using its home address regardless of the mobile node's current point of attachment to the Internet. Thus, the mobile node is able to communicate with other nodes, either stationary or mobile, after moving to a new network. And the movement of a mobile node away from its home link is also transparent to transport layer and higher-layer protocols applications.

In the following paragraphs, we introduce some components and terminology [3] used by Mobile IPv6.

Figure 1 Environment of MIPv6

(Adopted from “Understanding Mobile IPv6” of Microsoft co.)

․Home link : the link that is assigned the home subnet prefix of mobile node

․Home address (HoA) : an address assigned to the mobile node and through this address the mobile node is always reachable. A Mobile Node can have multiple home addresses. When the mobile node is away from home, packets destined to the mobile node's home address are intercepted by the home agent and tunneled to the mobile node's current location. The same as above, when the mobile node is at home network, MIPv6 processes are not used.

․Home agent (HA) : a router on the home link that maintains registrations of Mobile Nodes’ CoA (Care-of Address). When the MN (Mobile Node) is away from home, it registers its current address to home agent. The home agent tunnels data sent to the mobile node's home address to the mobile node's CoA (Care-of-Address) and forwards tunneled data sent by the MN (Mobile Node).

․Mobile Node (MN) : an IPv6 node that can change links and maintain reachability using its home address. A mobile node is aware of its home address and CoA (care-of address), and indicates its home address/care-of address mapping to the home agent and Correspondent Node with which it is communicating.

․Foreign link : a link other than MN's home link.

․Care-of address :a unicast routable address used by a Mobile Node while it is attached to a foreign link. For stateless address configuration, the care-of address is a combination of the foreign subnet prefix and an interface ID determined by the mobile node. A mobile node can be assigned multiple care-of addresses. Only one care-of address is registered as the primary care-of address with the mobile node's home agent. The association of a home address with a care-of address for a mobile node is known as a binding. CN (Correspondent Nodes) and HA (home agents) keep information on bindings in their binding cache.

․Correspondent Node : a peer node communicating with a MN (Mobile Node) is named as Correspondent Node. A correspondent node does not have to be Mobile IPv6-capable. A CN (Correspondent Node) can be either mobile or stationary.

․ Binding Update : the process to update the home agent with a new primary care-of address is known as a home registration binding update. There is also a binding of correspondent registration which runs between Mobile Node and Correspondent Node.

The home agent uses the home address in the Home Address option and the care-of address in a Care-of Address mobility option to update its Home Address/ Care-of Address binding cache entry for the mobile node.

Binding Cache : the table maintained by Home Agents and Correspondent node with Home Address of Mobile Node, Care-of address for mobile node and lifetime of binding cache entry.

MN will update its new location to an actively communicating Mobile IPv6-capable correspondent node with a binding that maps the home address of the mobile node to its care-of address. This process is known as a correspondent registration binding update. To update cache entry for Mobile Node’s Home Address/Care-of Address, the correspondent node uses the home address in the Home Address option and the source address of the packet.

Mobile IP protocol can handle movement in both wired and wireless local area and wide area of both wired and wireless networks. However, Mobile Node is required to notify its change of location to its home network. When moving to a foreign network, the care-of address (CoA) of Mobile Node has to be registered with its home agent. If there is a far distance between the foreign network and the home network of the mobile node, the signaling delay for these registrations may be long. This is why we have a proposal for distributed HA (Home Agent) which may be located in different geographical region to reduce the delay because of the distance.

To reduce the latency for real-time applications, a route optimization option will be necessary in Mobile IP. Therefore, Mobile IPv6 introduced a way for eliminating triangle routing by allowing Correspondent Nodes (CN) to cache bindings of the mobile nodes’

current locations. CN can then send packets for the mobile node directly to its care-of address without going through the home network. In the next section, we will give more details of Route Optimization feature of MIPv6.