Abstract:
A packet communication method of performing communication employing a packet having a transmission-source address and destination address, comprises the steps of: making a predetermined number of bits of the transmission-source address and a predetermined number of bits of destination address be fixed addresses; a repeating node for repeating a packet from a transmission-source terminal first converting the fixed address of the transmission-source address of the received packet into an address of an higher-rank station of the repeating node; and the repeating address converting the fixed address of the destination address of the received packet into an address of an higher-rank station of a last repeating node for a destination terminal, and transferring the packet.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a packet communication method, a node apparatus and a packet communication system. 
   2. Description of the Related Art 
   In the related art, an IP address is fixed for each host, and cannot adapt to a movement of the host. If an address is given for each movement of the host, the IP address is frequently changed, and, thereby, a traffic increases. Further, if the IP address is frequently changed, a case where the address of a mobile terminal cannot be obtained may occur, thereby other terminal cannot recognize the change in IP address, and cannot perform communication therewith. 
   In order to solve such a problem, it can be considered that a packet is changed into a capsule using a new address each time a host moves. 
   However, when a movement of host is made frequently, a load of a home station or the like increases because a time is required for changing the packet into a capsule and returning the capsule into the original packet. 
   Further, when an address of the other end of transmission is not known at a time of starting communication, it is necessary to transmit and receive a packet for inquiring the destination address. In such a case, a large time is required for transmitting the initial packet to the other end. 
   Furthermore, when a movement of a host is made frequently, packets for control generated together with address change increase, and, thereby, the traffic of information packets is suppressed. 
   SUMMARY OF THE INVENTION 
   The present invention has been devised in consideration of the above-mentioned problems, and, an object of the present invention is to provide a packet communication method by which, even when a repeating node is switched during communication, it is not necessary for a host to change an IP address, and it is possible to continue the communication only by path control or routing control. 
   A packet communication method of communication employing a packet having a transmission-source address and destination address, according to the present invention, comprises the steps of: 
   a) making a predetermined number of bits of the transmission-source address and a predetermined number of bits of destination address be fixed addresses (for example, FIXED (N00), in  FIG. 2 ); 
   b) a repeating node (for example, a mobile station  40 , shown in  FIG. 3 ), which repeats a packet from a transmission-source terminal (for example, a host computer  30 , shown in  FIG. 3 ) first, converting the fixed address of the transmission-source address of the received packet into an address (for example, B01, shown in  FIG. 3 ) of a higher-rank station (for example, a base station  50 , shown in  FIG. 3 ) of the above-mentioned repeating node; and 
   c) the above-mentioned repeating node converting the fixed address of the destination address of the received packet into an address (for example, B02, shown in  FIG. 3 ) of a higher-rank station (for example, a base station  51 , shown in  FIG. 3 ) of a last repeating node (for example, a mobile station  41 , shown in  FIG. 3 ) for a destination terminal (for example, a host computer  31 , shown in  FIG. 3 ), and transferring the packet. 
   The repeating node, which repeats the packet from the transmission-source terminal first, may convert the fixed address of the transmission-source address of the received packet into an address (for example, A01, shown in  FIG. 3 ) of a node (for example, an address management server  22 , shown in  FIG. 3 ) having a table of an address of a higher-rank station of a last repeating node for each terminal, when the address of the higher-rank station of the last repeating node for the destination terminal is not known, and transfers the packet. 
   The node having the table of the address of the higher-rank station of the last repeating node for each terminal may convert the own address in the destination address of the received packet into the address of the higher-rank station of the last repeating node for the destination terminal, and transfer the packet. 
   The higher-rank station of the repeating node, which repeats the packet from the transmission-source terminal first, may transfer the received packet without changing the transmission-source address, when the address of the higher-rank station in the transmission-source address of the received packet coincides with the address of the own station, and 
   convert the address of the higher-rank station in the transmission-source address of the received packet into the address of the own station, when the address of the higher-rank station in the transmission-source address of the received packet does not coincide with the address of the own station, and transfer the packet. 
   The higher-rank station of the repeating node, which repeats the packet from the transmission-source terminal first, may further instruct the higher-rank station having the transmission-source address written in the received packet to transfer a packet addressed to the above-mentioned transmission-source terminal to the own station, when the address of the higher-rank station in the transmission-source address of the received packet does not coincide with the address of the own station, and 
   further instruct the node having the table of the address of the higher-rank station of the last repeating node for each terminal to update the table. 
   The higher-rank station of the last repeating node for the destination terminal may transfer the received packet without changing the destination address when the address of the higher-rank station in the destination address of the received packet coincides with the address of the own station and no transfer instructions are given for the destination terminal, and 
   convert the address of the higher-rank station of the destination address of the received packet into an address of a higher-rank station of the destination of the thus-instructed transfer, when the address of the higher-rank station in the destination address of the received packet coincides with the address of the own station and transfer instructions are given for the destination terminal, and transfer the packet. 
   The higher-rank station of the last repeating node for the destination terminal may transfer the packet, when the address of the higher-rank station in the destination address of the received packet does not coincide with the address of the own station. 
   The higher-rank station of the last repeating node for the destination terminal may convert the addresses of the higher-rank stations in the transmission-source address and destination address of the received packet into the fixed addresses, and transfer the packet to the destination terminal. 
   In a case where the destination terminal belongs to another network (for example, an external IP network  130 , shown in  FIG. 7 ), 
   the transmission-source terminal may transmit the packet having an address given to the destination terminal as the destination address thereof; 
   the repeating node, which repeats the packet from the transmission-source terminal first, may convert the fixed address in the transmission-source address of the received packet into the address of the higher-rank station of the repeating node, and transfer the packet to a gateway station (for example, a gateway station  21 , shown in  FIG. 7 ) which provides an interface with the other network; and 
   the gateway station may convert the address of the higher-rank station of the received packet into the fixed address, and transfer the packet into the other network. 
   In a case where the transmission-source terminal belongs to another network (for example, an external IP network  130 , shown in  FIG. 8 ), 
   the transmission-source terminal may transmit a packet having an address given to the destination terminal as the destination address thereof; and 
   a gateway station (for example, a gateway station  21 , shown in  FIG. 8 ) which provides an interface with the other network may convert the fixed address in the destination address of the received packet into the address of the higher-rank station of the last repeating node for the destination terminal, and transfer the packet. 
   According to the present invention, it is possible to perform movement control of a mobile station only by path control or routing control in a base station network. 
   Further, even when a base station to which a terminal belongs is switched due to a movement or change in radio propagation condition, a traffic of path-control or routing-control information in a base station network does not increase. 
   Furthermore, it is possible to prevent a packet from being discarded due to destination of transfer being unknown due to a movement of a mobile station. 
   Further, an address of a mobile host is not changed even at a receiving side. 
   Further, even when a mobile station changes a base station to which the mobile station belongs during communication, it is not necessary to specially transmit a control packet for reporting the change of the base station to which the mobile station belongs. 
   Further, even when a repeating node is changed during communication, it is possible to continue the communication only by path control or routing control without changing an IP address at a host. 
   Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a packet mobile radio communication system; 
       FIG. 2  illustrates a configuration of an address of a packet according to the present invention; 
       FIG. 3  illustrates a communication procedure at a time of starting communication; 
       FIG. 4  illustrates a communication procedure of normal communication; 
       FIG. 5  illustrates a communication procedure in a case where a base station to which a transmission-source host belongs is switched to another base station; 
       FIG. 6  illustrates a communication procedure in a case where a base station to which a destination host belongs is switched to another base station; 
       FIG. 7  illustrates a communication procedure in a case where a destination of transmission is in an external IP network; 
       FIG. 8  illustrates a communication procedure in a case where a transmission source is in an external IP network; and 
       FIG. 9  shows a block diagram of each of mobile stations, base stations, address management station and gateway station shown in  FIGS. 1 ,  3  through  8 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An embodiment of the present invention will now be described with reference to figures. 
   The description will be made for an example of a packet mobile radio communication system. 
   The packet mobile radio communication system in the example has a configuration shown in  FIG. 1 . 
   As shown in  FIG. 1 , the packet mobile communication system includes a mobile station (MS)  17 , another mobile station  18 , a terminal (HOST: host computer)  19 , a base station network (BS network)  20 , a gateway station (GW)  21  for providing an interface with another network, an address management server (AMS)  22 , the IP network  130 , and another terminal (HOST: host computer)  39  of the IP network  130 . The base station network  20  includes, for example, base stations (BS)  11  through  16 . 
   One or a plurality of terminals (host computers: host) are connected to one mobile station. The address management server (AMS)  22  manages the number (host ID) special to each host and the number (base station ID) special to a base station to which a mobile station to which the host is connected belongs. The address management server  22  has an address management table which is a table of each host ID and the base station ID of the base station to which the host is connected via the mobile station. Further, the gateway station  21  provides an interface with another network (the IP network  130 ), and has an address management table, same as the address management server  22 . 
     FIG. 2  shows a configuration of an address according to the present invention. 
   The address includes a network part and a host part. The network part is an address special to a network. 
   The address of the host part is a combination of an address (host ID) special to the host and an certain fixed address (FIXED: N00). In a mobile station, the part of the fixed address is replaced by a base station ID of the base station to which the mobile station belongs (base station ID field). 
   In description of the embodiment of the present invention which will now be described, each mobile host belonging to a communication network is registered to the address management server at a time of starting up of the mobile station or at a time of releasing from a sleep state, and, at a time of starting communication, a host of transmission source knows the ID of the base station to which the host belongs. Further, in the address management server, the correspondences in ID between the mobile hosts belonging to the communication network and the base stations to which the hosts belong are updated into the latest ones. 
   1. First, a case where a destination host is included in the same communication network will now be described. 
   (1) At a time of starting communication 
   A communication procedure at a time of starting communication will now be described with reference to  FIG. 3 . 
   A case will now be described where a packet is transmitted from a host  30  having a host ID of H01 connected to a mobile station  40  belonging to a base station  50  having a base station ID of B01 to a host  31  having a host ID of H02 connected to a mobile station  41  belonging to a base station  51  having a base station ID of B02. 
   {circle around (1)} A packet having the transmission-source address and the destination address of N00/H01 and N00/H02 is transmitted from the host  30 . 
   {circle around (2)} The mobile station  40  replaces the base station ID field of the transmission-source address with the address B01 of the base station  50  to which the mobile station  40  belongs. Because the ID of the base station  51  to which the host  31  of the destination belongs is not known, the mobile station  40  replaces the base station ID field with A01 which is the ID of the address management server  22 . Then, the mobile station  40  transfers the thus-obtained packet into the base station network  20 . 
   {circle around (3)} In the base station network  20 , the packet is transferred to the address management server  22  having the address A01 which is the destination node of the packet. The address management server  22  refers to the address management table, and replaces the base station ID field of the destination address with B02 which is the address of the base station  51  to which the host  31  belongs. Then, the address management server  22  transfers the thus-obtained packet into the base station network  20 . 
   {circle around (4)} The mobile station  41  receives the packet transferred by the address management server  22  via the destination base station  51  (B02). Further, the mobile station  41  knows from the transmission-source address of the received packet that the base station ID of the base station to which the host  30  (H01) belongs is B01. Then, the mobile station  41  stores it in an address conversion table of the own station. 
   {circle around (5)} Further, the mobile station  41  replaces the base station ID field of each of the transmission-source address and destination address with N00, and transmits the thus-obtained packet to the host  31  (H02). 
   Thereby, according to the present invention, it is possible to transfer the packet from the management server without executing processes of inquiring the address of a host of the other end and receiving the answer thereto. 
   (2) Normal Communication 
   A communication procedure of normal communication will now be described with reference to FIG.  4 . 
   A case will now be described where a packet is transmitted from the host  30  having the host ID of H01 connected to the mobile station  40  belonging to the base station  50  having the base station ID of B01 to the host  31  having the host ID of H02 connected to the mobile station  41  belonging to the base station  51  having the base station ID of B02. 
   {circle around (1)} A packet having the transmission-source address and the destination address of N00/H01 and N00/H02 is transmitted from the host  30 . 
   {circle around (2)} (In this case, it is assumed that a process such as that described above in the item (1) has been performed from the host  31  to the host  30  so that the address conversion table of the mobile station  40  has the base station ID B02 of the base station  51  to which the host  31  belongs, as shown in  FIG. 4 .) According to the address conversion table, the mobile station  40  replaces the base station ID field of the transmission-source address with the address B01 of the base station  50  to which the mobile station  40  belongs. On the other hand, the mobile station  40  replaces the base station ID field of the destination address by B02 which is ID of the base station  51  to which the destination host  31  belongs. Then, the mobile station  40  transfers the thus-obtained packet into the base station network  20 . 
   {circle around (3)} The packet is transferred to the mobile station  41  which belongs to the base station  51  (B02) via the base station  51  of destination. Then, the mobile station  41  replaces the base station ID field of each of the transmission-source address and destination address with N00, and transfers the packet to the host  31  (H02). 
   (3) A case where a base station to which a transmission-source host belongs is switched to another base station 
   With reference to  FIG. 5 , a communication procedure in a case where a base station to which a transmission-source host belongs is switched to another base station will now be described. 
   A case where, during a process of transmitting a packet from the host  30  having the host ID of H01 connected to the mobile station  40  belonging to the base station  50   1  having the base station ID of B01 to the host  31  having the host ID of H02 connected to the mobile station  41  belonging to the base station  51  having the base station ID of B02, the base station to which the host  30  (H01) belongs is switched into a base station  50   2  (B03) will now be described. 
   {circle around (1)} The mobile station  40 , when converting the addresses, replaces the base station ID field of the transmission-source address with B01 which is the address of the original base station  50   1 , and transmits the packet to the base station  50   2  (B03). 
   {circle around (2)} The base station  50   2  (B03), receiving the packet, 
   (i) replaces the base station ID field of the transmission-source address by B03 which is the address of its own, and transmits the packet to the base station network  20 ; and 
   (ii) knows from the original contents of the base station ID field of the transmission-source address that the address of the base station  50   1  to which the host  30  originally belongs is B01 and transmits, to the base station  50   1 , a packet instructing the base station  50   1  to transfer a transferred packet addressed to the host  30  (H01) to the base station  50   2  (B03). At the same time, also to the address management server  22 , the base station  50   2  (B03) transmits a packet instructing the address management server  22  to update the base station to which the host  30  (H01) belongs into B03. 
   {circle around (4)} After that, the process same as that in the case of normal communication is executed. 
   (4) A case where a base station to which a destination host belongs is switched to another base station 
   With reference to  FIG. 6 , a communication procedure in a case where a base station to which a destination host belongs is switched to another base station will now be described. 
   A case where, during a process of transmitting a packet from the host  30  having the host ID of H01 connected to the mobile station  40  belonging to the base station  50  having the base station ID of B01 to the host  31  having the host ID of H02 connected to the mobile station  41  belonging to the base station  51   1  having the base station ID of B02, the base station to which the host  31  (H02) belongs is switched into a base station  51   2  (B04) will now be described. 
   {circle around (1)} In the manner same as that in the normal communication, the packet is transferred to the base station  51   1  (B02) via the base station network  20 . 
   {circle around (2)} The base station  50   1  (B02) previously receives instructions to transfer a packet addressed to the host  31  (H02) to the base station  51   2  (B04) when receiving the packet addressed to the host  31  (H02), when the base station to which the host  31  (H02) belongs is switched to the base station  51   2  (B04), then replaces the base station ID field of the destination address of the received packet with B04, and transfers the packet to the base station network  20 . 
   {circle around (3)} After that, the process same as that in the normal communication is executed. 
   2. A case where a host on the other end of transmission is in an external IP network 
   (1) A case where a packet is transmitted from the host  30  having the host ID of H01 connected to the mobile station  40  belonging to the base station  50  having the base station ID of B01 to a host  37  in an external IP network  130  will now be described with reference to  FIG. 7 . 
   {circle around (1)} A packet having the transmission-source address and destination address of N00/H01 and Hxx is transmitted from the host  30 . 
   {circle around (2)} The mobile station  40  first replaces the base station ID field of the transmission-source address with the address B01 to which the mobile station  40  belongs. On the other hand, when the destination host  37  is in the external IP network  130 , the mobile station  40  does not change the destination address, and transmits the packet into the base station network  20 . 
   {circle around (3)} In the base station network  20 , when the destination of the packet is in the external IP network  130 , the packet is transferred to the gateway station  21 . 
   {circle around (4)} The gateway station  21  replaces the base station ID field of the transmission-source address by the fixed address N00, and transmits the packet into the external IP network  130 . 
   (2) A communication procedure in a case where a packet transferred from an external IP network  130  and addressed to the host  31  having the host ID of H02 is transferred to the host  31  (H02) connected to the mobile station  41  belonging to the base station  51  having the base station ID of B02 will now be described with reference  FIG. 8 . 
   {circle around (1)} The packet transferred from the external IP network  130  has the base station ID field of the destination address thereof replaced with B02 and is transmitted to the base station network  20  by the gateway station  21  according to the address management table. 
   {circle around (2)} The packet is transferred to the mobile station  41  belonging to the destination base station  51  (B02) via the base station  51 . Then, the mobile station  41  replaces the base station ID field of the destination address with the fixed address N00, and transfers the packet to the host  31  (H02). 
   Operations performed by a base station will now be described. 
   (1) Operations in a case where a radio packet from a mobile station is received 
   (i) When the base station ID in the transmission-source address of the packet coincides with the address of the own station, the base station transfers the packet as it is to another base station, mobile station, the address management server or the like according to path control or routing control. 
   (ii) When the base station ID in the transmission-source address of the packet does not coincide with the address of the own station, the base station replaces the base station ID with ID of the own station, and instructs the base station having the original ID to transfer a packet addressed to the transmission-source host of the above-mentioned packet to the current base station. Simultaneously, the base station instructs the address management server to update the address management table accordingly. 
   (2) Operations in a case where a packet from another base station or the like is received 
   (i) When the base station ID of the destination address of the packet coincides with the address of the own station, and, also, no instructions of transfer has been given, the base station transmits the packet to the mobile station to which the destination host belongs. 
   (ii) When the base station ID of the destination address of the packet coincides with the address of the own station, and, also, instructions of transfer has been given, the base station replaces the base station ID of the packet with ID of the base station which is the destination of the thus-instructed transfer, and transfers the packet. 
   (iii) When the base station ID of the destination address of the packet does not coincide with the address of the own station, the base station transfers the packet to another base station according to path control or routing control. 
   Operations of a mobile station will now be described. 
   (1) The mobile station transfers a packet from a host to a base station. At this time, the mobile station replaces the base station ID field of the transmission-source address of the packet with ID of the base station to which the own station belongs, and replaces the base station ID field of the destination address with ID of the base station to which the mobile station to which the destination host is connected belongs. 
   When the ID of the base station to which the mobile station to which the destination host is connected belongs is not known, the mobile station replaces the base station ID field of the destination address with ID of the address management server. 
   (2) The mobile station transfers a packet from a base station to a host. At this time, the mobile station returns the base station ID field of each of the destination address and transmission-source address of the packet into the original fixed number (FIXED: fixed address). 
   (3) In order to achieve the above-mentioned operations of (1) and (2), the mobile station detects and stores the correspondences in ID between the transmission-source and destination hosts and the base stations to which the hosts belong, respectively, and performs address conversion according thereto. 
   The address management server in the above description manages the correspondence between each host ID and the base station ID of the base station to which the mobile station to which the host having the host ID is connected belongs. The address management server updates the management data each time the base station to which the mobile station belongs is updated. 
   Although the above description is one for the example of the mobile radio communication system, the present invention may also be applied to a fixed wire communication system. 
   Each of the mobile stations, base stations, address management server and gateway station in the system described above according to the present invention may have a block configuration as shown in  FIG. 9 . 
   As shown in  FIG. 9 , each of the mobile stations, base stations, address management server and gateway station includes a receiver  201 , a repeating part  202 , a transmitter  203  and a data processing part  204 . The receiver  201 , repeating part  202  and transmitter  203  may be those well-known in the art employed by general repeaters used in a common communication networks. In a case of the gateway station, these parts further have functions of gateway well-known in the art used for linking two different types of networks, commonly. 
   The data processing part  204 , which may include a CPU, a memory and other storage devices, as the need arises, performs the various operations of each of the mobile stations, base stations, address management server and gateway station described above with reference to  FIGS. 2 through 8 . 
   The present invention is not limited to the above-described embodiment, and variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority applications Nos. 11-371597 filed on Dec. 27, 1999, the entire contents of which are hereby incorporated by reference.