THE BASIC OPERATION OF MOBILE IPV6 IN GPRS/WCDMA NETWORK

When the mobile terminal is roaming in a foreign network, it is addressable by a care-of address, in addition to its home address. The IPv6 address prefix in the mobile terminal’s care-of address is the prefix of the foreign link. The care-of address is acquired by the addressing mechanism provided by the visited network. While roaming in the foreign network, the mobile terminal registers one of its care-of addresses with the home agent and sends a “Binding Update” to the home agent. The home agent replies with “Binding Acknowledgement.” Any IPv6 packets containing Binding Update or Binding Acknowledgement destination options must be authenticated using IP Security AH (Authentication Header). After the binding, this care-of address becomes the mobile terminal’s primary care-of address.

The home agent intercepts all IPv6 packets from a correspondent node (for example a WWW server that is communicating with the mobile terminal) addressed to the mobile terminal’s home address. The home agent encapsulates each intercepted packet using IPv6 encapsulation, with the outer header addressed to the mobile terminal’s primary care-of address. After the mobile terminal has received the first encapsulated packet from the home agent, it sends a Binding Update to the correspondent node informing it of its care-of address: the correspondent node then replies with a Binding Acknowledgement. After this, sending IP packets between the correspondent node and the mobile terminal is straightforward and routing via a home agent is not needed. For packets sent by a mobile terminal while away from home, the mobile terminal’s care-of address is typically used as the source address in the packet’s IPv6 header. The Home Address option can be used to inform the packet recipient of the mobile node’s home address.

The correspondent node can then substitute the mobile node’s home address for this care-of address making the use of the care-of address transparent to the correspondent node. The upper protocol layers (e.g. TCP) thus only see the home address.

MOBILE IPV6 FOR INTER-PLMN MOBILITY

Consider the situation that a GPRS subscriber of an operator in Finland is roaming in the U.S. and accessing a local service there. If the link layer mobility were used, the user’s IP packets would first be tunnelled to Finland, and then routed back to the U.S. In this scenario a round trip time from the mobile terminal to a server and back could be unacceptable to many services. As a solution to this problem, the roaming GPRS subscriber should use the services of a local GGSN in the visited network, allowing IP packets to be routed as soon as possible, without crossing over to the home network. As the IP address is now being assigned from the visited network, the mobile node would not be accessible via a network layer identity of the home network. For some applications this may not be a problem, but in general it would be desirable if the mobile node could be reached with an IP address being assigned from the home network as well. A natural solution to this problem is to use Mobile IP to register the visited network address with the home network, allowing packets sent to the home address to be delivered to the mobile node.