10.1 INTRODUCTION

As the size and weight of terminals and battery become smaller and lighter, the mobile computing and communications becomes real in the every day of life. Mobility service is considered as one of the killer applications in IPv6. Agents usually are in charge of the management of node's mobility as well as address allocations. They help roamed mobile nodes to get message properly.

In IPv4, a mobile node may be identified by its home address, irrespective of the location where the mobile node currently resides. When a mobile node is located away from its home, the mobile node can not communicate with its home address because the prefix of the current link is different from the prefix of the home address. The current access router can not support the routing of packets using the home address. The mobile node should use addresses which are topologically correct. Thus, the mobile node should be allocated a new address in the visiting link. This address is called care-of address (CoA).

In Mobile IPv4 (MIP _v4), ^[1] CoA is allocated by foreign agents which take care of the link where the mobile node currently resides. A CoA obtained in this way is called foreign agent CoA . It is actually IP address assigned to one of interfaces of the foreign agent. CoA may be allocated using DHCP. ^[2] This CoA is called co-located CoA .

In Mobile IPv6 (MIPv6), ^[3] CoA may be allocated by stateless or stateful approaches. Stateful...