| Nowadays mobile communication and Internet grow up rapidly and interact each other. There are all kinds of portable terminals. More and more mobile users want to connect with Internet neatly and at anywhere, share the rich and colorful service of Internet. The hosts based on traditional IP communicate with each other using fixed IP and port. During communication, IP and TCP port can't change, otherwise they can't communicate with each other any more. In order to solve this problem, IETF puts forward mobile IPv4 in 1996, but MIPv4 can't provide good mobility service. So IETF works out mobile IPv6. MIPv6 uses the characteristic and auspice for mobile in IPv6, its address is 128 bit instead of 32, and it can distribute every host a global IP, and mobile host can keep connection with Internet when it is moving.Mobile IPv6 solves the problem that provides mobile users seamless roaming. But in mobile IPv6, when mobile node moves, it must send binding update packet to home agent and all corresponding nodes in order to keep intrinsic communication not interrupted. If mobile node often changes its location, and there are many corresponding nodes, there will be many binding update packets on Internet. It is proved that mobile node often moves within a domain, so IETF puts forward "hierarchical mobile IPv6 mobility management (HMIPv6)". It can reduce the amount of binding update packets, and it can hide the location of the mobile node. So in order to improve the service of mobile IP, the research on HMIPv6 has important academic and practical meaning.This paper analyses HMIPv6 in detail based on the study of MIPv6 and according to the 8th IETF draft of HMIPv6. There is a new entity—MAP besides mobile node, home agent and corresponding node in HMIPv6. MAP can be any router in the network, and there can be many MAPs in the network, they can have hierarchy if necessary. It acts as local home agent. It often locates at boundary of network, and there can be many access routers below it. Thus there is hierarchy in the network, and the movement of the mobile node is divided into intra-site mobility (within a MAP domain) and inter-side mobility (from one MAP domain to another). When mobile node moves within a MAP domain, because it is transparent to home agent and corresponding nodes, it reduces the amount of binding update packets. Because mobile node is near MAP, it is quick that updates MAP' binding cache, it reduces packets delay and packet loss rate because of hand-off. The mobile node obtains an IP address based on its home link network prefix when it connects to network at first time. When on the home link, mobile nodes just act as static ones.When mobile node finds it has moved by Neighbor Discovery, it must form tow care-of address: Regional Care-of address (RCoA) and On-link CoA (LCoA). Using stateless address configuration in IPv6, the mobile node based on MAP's prefix forms RCoA, and based on Access Router's prefix forms LCoA.When mobile node moves within a MAP domain, it receives the same MAP option message. So the RCoA of mobile node does not change. Because the access router has changed, the LCoA of mobile node changes. In this case, mobile node need not send binding update packets to home agent and corresponding nodes, it only needs to send binding update packet to MAP, and use new RCoA and LCoA updating the old binding.When mobile node finds its MAP changed by analysing MAP option message, namely mobile node moves from one MAP domain to another, both the RCoA and the LCoA of mobile node change. After configurating RCoA and LCoA, mobile node need to send binding update packet to the new MAP to register its new RCoA and LCoA, then send binding update packets to home agent and corresponding nodes to register its home address and its new RCoA.The operation of the home agent and corresponding node is the same as in mobile IPv6. When mobile node at foreign link, the corresponding node check its binding cache to find whether there is mobile node's binding before it sends packet to mobile n...
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