1. Field of the Invention
The present invention relates to a mobile node, a base station, and a router in a packet communication system conforming to Edge Mobility, and relates to the packet communication system.
2. Description of the Related Art
In the Internet using the Internet Protocol version 6 (IPv6) (refer to non-patent document 1, for example), Mobile IPv6 (refer to non-patent document 2, for example) exists as a technology for enabling a node to keep communications with another node that is a communication partner even though the node moves so that links to which the node connects successively change.
The Mobile IPv6 defines a mobile node (MN) that moves in the Internet and a home agent (HA) that exists on a predetermined link in the Internet and that transfers a packet addressed to the MN to the MN.
The MN uses a home address (HoA) determined from the link where the HA exists and a care of address (CoA) determined from a link where the MN currently exists. The MN updates CoA every time when the MN moves. Then, the MN reports binding information indicating correspondence between HoA and CoA to the HA using a Binding Update (BU) message. The HA encapsulates a packet addressed to the HoA of the MN sent by a communication partner into a packet addressed to CoA indicated by the binding information. In the Mobile IP, communications between the MN and the partner node are ensured according to the above-mentioned operations.
Edge Mobility (refer to non-patent document 3, for example) is another technology for providing mobility on the IP layer like the Mobile IPv6. Compared with Mobile IPv6, the Edge Mobility has merits in that control signals in wireless sections and overheads can be decreased and that topology information of nodes can be hidden. On the other hand, according to the Mobile IPv6, topology information and geographical position of the MN can be estimated by referring to a Network Prefix in CoA.
Edge Mobility defines an access router that is a default router of the MN, and a routing manager (RM) for managing mapping of addresses corresponding to the MN. In addition, the Edge Mobility defines two kinds of addresses that are IP host address (IPha) and IP routing address (IPra) as addresses for transferring a packet to MN.
The IPha is an address which the MN recognizes as its own address. When communicating with an arbitrary MN, an IPha of the communication partner is designated as a destination address and an IPha of the MN is designated as a source address. Although the IPha can be used for transferring an IP packet among sections of MN—mobile station (Node B)—AR, the IPha cannot be used for transferring a packet in the Core Network (CN) that exists ahead of the AR. The IPra is an address of the MN that can be used for transferring the IP packet in the Core Network (CN).
The AR obtains the IPha and IPra of a MN under the AR, and obtains the IPha and IPra of a communication partner MN from the RM. The AR converts IPha in an IP header of a packet transferred from the Radio Access Network (RAN) to the CN into IPra, and converts IPra in an IP header of a packet transferred from the CN to the RAN into IPha.
A concrete example of packet transfer is described with reference to FIG. 1.
For example, MN_A sends a packet for MN_B (1). In this case, the destination is IP host address of the MN_B. The IP host address is an IP address held by MN, and that is not applicable for Routing in the Core Network as mentioned above.
The transmitted packet is transferred to the AR. The AR obtains, from the RM, IPha and IPra of the MN under the AR and IPha and IPra of the transmission destination. The RM holds address correspondences for all MNs residing in the network. In addition, the AR converts each of source and destination addresses in the IP header of the transmitted packet addressed to the MN_B from IP host address to IP routing address (2). As mentioned above, the IP routing address is an address that corresponds to the IP host address and that can be used for routing in the Core Network.
The address-converted packet addressed to the MN_B is transferred to an upper AR of the MN_B. The upper AR of the MN_B converts each of source and destination addresses of the IP header of the packet addressed to the MN_B from IP routing address to IP host address, and transfers the packet (3). The transferred packet addresses to the MN_B is received by the MN_B (4).
In Edge Mobility, according to the above-mentioned method, since a MN can ascertain only IP address of the destination MN, topology information is hidden. In addition, by performing address conversion, header overhead due to header encapsulation performed in Mobile IPv6 does not arise. Following are documents relating to the present application:                [Non-patent document 1] S. Deering and R. Hinden, “Internet Protocol, Version 6 (IPv6) Specification”, Request For Comments 2460, December, 1998;        [Non-patent document 2] D. Johnson, et al., “Mobility Support in IPv6,” Request For Comments 3775, June, 2004;        [Non-patent document 3] Okagawa et. al. “IP packet routing mechanism in IP2”, IEICE, IN-MoMuC study group, November 2002;        [Non-patent document 4] 3GPP TS 23.003V6.2.0, “Numbering, addressing and identification (Release 6)”, March, 2004;        [Non-patent document 5] R. Hinden, et al., “IP Version6 Addressing Architecture”, Request For Comments 2373, July, 1998.        
However, the above-mentioned conventional technology includes the following problems.
In Edge Mobility, since the topology information is hidden by address conversion, the IP address that can be used for packet transfer in RAN is IPha. Network Prefix of the IPha is the same for every mobile node MN. Therefore, the RAN as a whole becomes a large subnet. Therefore, there is a problem in that generation of a routing table and packet transfer using Network Prefix, which are performed in IP, cannot be performed.
To solve this problem, there is a method in which the Node B performs frame switching on layer 2 so as to perform routing in the RAN in layer 2. However, in this case, it is necessary to use Neighbor Discovery Protocol (NDP) as a layer 2 address resolution method when the mobile node MN transmits a packet, and when the AR transfers a packet to the mobile node MN. There is a problem in that NDP affects traffic in wireless links in which bandwidth is limited.
An object of the present invention is to provide a mobile node, a base station, a router and a packet communication system that can perform optimum routing and forwarding by IP in RAM formed by nodes and links conforming to Edge Mobility.