Abstract:
In an access point device, a controller controls a wired interface communicating on wire with a network switcher accommodating access point devices and a wireless interface communicating wirelessly with a wireless terminal device located in its service area. Services are handed over between the access point devices responsively to the wireless terminal device moving. Access point devices before and after the handover of services are defined as a handover source and a hand over destination, respectively. A hand over at the hand over destination causes a data frame to be generated containing the MAC address of the wireless terminal device as a source address, a broadcast address as a destination address and address information of its own device. A table holds terminal connection information defining the relationship of the MAC address to the IP address of the wireless terminal device. The data frame is transmitted to the network switcher through the wired interface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an access point device and a communications system, and is applicable, for example, to a method of updating terminal connection information held in a network switcher according to a handover process that is performed between access point devices. 
     2. Description of the Background Art 
     A description will be given of a conventional method in which a wireless VoIP (Voice over Internet Protocol) terminal is handed over on a wireless local area network (LAN). A plurality of access point devices are connected to some of the ports of a network switcher, one of the remaining ports being connected to an external network through a router. Note that the external network has external terminal devices connected thereto. The access point devices each has a wired-LAN interface, a controller, and a wireless LAN interface. A wireless LAN terminal device is connected to any access point device and communicates with that device. 
     If the wireless LAN terminal device connected to one access point device moves during communication and enters the administration area of another access point device, the wireless LAN terminal device is handed over from the previous access point device to the next access point device to be reconnected to the next access point device. 
     Such a handover technique between access point devices is disclosed in Japanese patent laid-open publication No. 2004-229225 by way of example. 
     When a wireless LAN terminal device is moving during communication and the handover process is being executed between access point devices, a frame is sometimes transferred from an external terminal device to this wireless LAN terminal device. At this time, a MAC (Media Access Control) address table in the network switcher has not been updated yet. The MAC address table defines the relationship of the MAC address of a wireless LAN terminal device with a corresponding switcher port number, etc. Because of the MAC address table not updated, there may be cases where the relay of a frame to the wireless LAN terminal device is unsuccessful. 
     As a technique for avoiding such a case, there has been proposed a method in which the next access point device receiving a reconnection request after movement of a wireless LAN terminal device transmits a dummy data frame in which the MAC address of the wireless LAN terminal device is inserted in its destination address field, and a network switcher receiving the dummy data frame updates the connection information in its MAC address table that corresponds to the wireless LAN terminal device. In addition, for example, some conventional access point devices are equipped with a proxy address resolution protocol (ARP) function which, when receiving an ARP request for the IP (Internet Protocol) address of a destination LAN terminal device to be relayed by its own device, replies to the ARP request by proxy, in order to reduce the necessity to transmit the ARP request to the wireless LAN terminal device to be connected and reduce the power consumption of the wireless LAN terminal device. 
     However, in the case of adopting the above-described method in which the next access point device connected after movement of the wireless LAN terminal device transmits a dummy data frame to the network switcher, there arises a problem that this access point device has to transmit the unnecessary data frame. 
     In the case of utilizing the above-mentioned proxy ARP function equipped in the access point device, the access point device normally cannot use the proxy ARP function until it receives an IP packet from the wireless LAN terminal device connected thereto. 
     Therefore, even if frames are transmitted from an external terminal device to the wireless LAN terminal device, in the access point device the proxy ARP function cannot be executed until it receives an IP packet from the wireless LAN terminal device and identifies the IP address of the wireless LAN terminal device, and consequently, there will arise another problem that frames cannot be relayed. 
     In addition, the handover source, that is, the previous access point device continues to have the proxy ARP function of the wireless LAN terminal device which is no longer located within its administration area. Because of this, the previous access point device sometimes replies to an ARP request. This replay gives rise to ARP inconsistency, whereby there is a possibility that trouble will occur in the operation of the entire network. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an access point device and a communications system that are capable of effectively using the proxy ARP function, and that are capable of updating the connection information of a wireless LAN terminal device in a network switcher immediately after the wireless LAN terminal device is handed over, without causing network trouble. 
     In accordance with the present invention, there is provided an access point device connectible with a wireless terminal device. The access point device comprises a wired interface for establishing wired communication with a network switcher that is connected with or accommodates a plurality of access point devices, including the access point device, and a wireless interface for establishing wireless communication with the wireless terminal device located within its service area. The access point device also comprises a controller comprising a generation functional block responsive to a handover at the handover destination for generating a data frame so that it contains physical address information of the wireless terminal device as a source address, a broadcast address as a destination address and address information of its own device, where the handover is defined as handing services over between the access point devices in response to the wireless terminal device moving, the handover source is defined as an access point device before the handover of the services, and the handover destination is defined as an access point device after the handover of the services. The access point device further comprises a table for holding terminal connection information in which the physical address information is related to network address information of the wireless terminal device. The controller transmits the generated data frame to the network switcher through the wired interface. 
     According to the access point device and communications system of the present invention, under the control of the controller the access point device of the handover destination sends to the network switcher a data frame which contains the network address information of the wireless terminal device as a source. Therefore, immediately after the wireless terminal device has been handed over, the network switcher is able to update the connection information of the wireless terminal device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic block diagram showing the configuration of a preferred embodiment of a wireless communications system to which the present invention is applied; 
         FIG. 2  is a schematic block diagram showing the functions of the controller of the wireless communications system shown in  FIG. 1 ; 
         FIG. 3  schematically show the fields of a proxy ARP request frame handled by the wireless communications system shown in  FIG. 1 ; 
         FIG. 4  is a sequence chart showing how the wireless communications system shown in  FIG. 1  is operated; 
         FIG. 5  schematically illustrates the frame structure of an ARP request handled in the operation of  FIG. 3 ; and 
         FIG. 6  is a schematic block diagram showing the configuration of an alternative embodiment of the wireless communications system to which the present invention is applied. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of a communications system according to the present invention will be described in detail with reference to the accompanying drawings. Referring to  FIG. 1 , there is shown a wireless communications system  10  constructed in accordance with a preferred embodiment of the communications system of the present invention. In the wireless communications system  10 , under the control of a controller  50  an access point device  16  of a handover destination sends to a network switcher  12  a request frame in which the IP (Internet Protocol) address of a wireless terminal device  20  is a source address, whereby the connection information of the wireless terminal device  20  in the network switcher  12  can be updated immediately after the wireless terminal device  20  has been handed over to the access point device  16 . 
     In the preferred embodiment, the communications system of the present invention is applied to the wireless communications system  10 . In the figures, part of the circuitry not directly relevant to the understanding of the present invention is not shown, and detailed description thereof will not be made in order to avoid redundancy. In the following description, signals are designated with reference numeral indicating connections on which signals are transmitted. 
     As shown in  FIG. 1 , the wireless communications system  10  comprises a network switcher  12 , a plurality of access point devices  14 ,  16 , and  18 , and a wireless local area network (LAN) terminal device  20 . The network switcher  12  has the function of switching a MAC (Media Access Control) frame of the wireless LAN terminal device  20  based on the MAC address and transferring the MAC frame to its destination. In the preferred embodiment, the network switcher  12  has five physical ports  22 ,  24 ,  26 ,  28 , and  30 . The physical port  22  of the network switcher  12  is connected to, or accommodates, the access point device  14  by a signal line  32 , the physical port  26  is connected to the access point device  16  by a signal line  34 , and the physical port  30  is connected to the access point device  18  by a signal line  36 . 
     If the access point devices  14 ,  16 , and  18  respectively connected with the ports of the network switcher  12  may be identical with one another in construction, the access point devices  14 ,  16 , and  18  form the same broadcast domain. The wireless communications system  10  establishes broadcast communications by forming this domain. 
     The network switcher  12 , as with switchers having a general function of transmitting and receiving information, has an MAC address table  38  in which the MAC addresses of the wireless LAN terminal device  20 , etc., transmitted and received by its own device  12  are related with the port numbers, device identification of the access point device  18 , etc. The MAC address table  38  updates stored contents as needed according to a change in the state of connections, etc. The network switcher  12  is able to connect with an external network through a router, etc., and may relay data between an external terminal device on the external network and the wireless LAN terminal device  20  on the wireless LAN. 
     Note that the network switcher  12  may be an existing network switcher. Because the internal construction of the network switcher  12  does not form part of the present invention, a description of the internal configuration will not be given. 
     The access point devices  14 ,  16 , and  18  each have an administration or service area, and administer communication between the wireless LAN terminal device  20  located within this area and a destination terminal device on a wired LAN. The access point devices  14 ,  16  and  18  have the function of relaying MAC frames received. The access point devices  14 ,  16 , and  18  each include the same components. Particularly, the components comprised in the access point devices  14  and  16  are shown in  FIG. 1 . The access point device  14  includes a wired-LAN interface  40 , a controller  42 , a wireless LAN interface  44 , and a proxy ARP table  46 , which are interconnected as illustrated. The access point device  16  comprises a wired-LAN interface  48 , a controller  50 , a wireless LAN interface  52 , and a proxy ARP table  54 , which are interconnected as illustrated. The access point device  18  likewise comprises a wired-LAN interface, a controller, a wireless LAN interface, and a proxy ARP table, although not shown. 
     Now, the major components of the access point device  14  will be described. The wired-LAN interface  40  has the function of interfacing with a wired LAN. The wired LAN in the preferred embodiment is constructed to establish communication according to Ethernet (trademark) standards. The wired-LAN interface  40  communicates with the controller  42 . 
     As shown in  FIG. 2 , the controller  42  includes a communication control functional block  42 A, a proxy address resolution protocol (ARP) functional block  42 B, an address generation functional block  42 C, a registration functional block  42 D, a retrieval functional block  42 E, and a deletion functional block  42 F. The communication control functional block  42 A has a function which, according to a result of being contained or listed in the proxy ARP table  54  of the handover destination, sets the corresponding data of the table  54  so that the wireless terminal device  20  is a destination, and transmits the set data frame to the handover source, and which, according to a result of not being contained in the proxy ARP table  54 , discards the supplied data frame. The communication control functional block  42 A not only has the function of controlling wire and wireless communications in the access point device  14  mutually, but also controls transmission and reception, discarding of data, as described above. 
     The replay function, the proxy ARP functional block  42 B, of the controller  42  has a function which, in response to the transmission of a data frame from the access point device  16  of the handover destination to the access point device  14  of the handover source, sends a request for the MAC address of the wireless terminal device  20  from the handover source to the access point device  16  of the handover destination having an IP address, references information stored in the proxy ARP table  54  in response to this request with the access point device  16  of the handover destination, and sends back the MAC address of the wireless terminal device  20  to the handover source. The address generation functional block  42 C has the function of generating a data frame which contains the MAC address of the wireless LAN terminal device  20  inserted in the source address field, a broadcast address inserted in the destination address field, and its own address. 
     The registration functional block  42 D has the function of receiving a data frame at a handover destination, and adding and registering the received data. Specifically, the registration functional block  42 D is the function of registering the generated MAC address and broadcast address in the proxy ARP table  46  as a set of data related to each other. 
     The retrieval functional block  42 E has the function which, in response to reception of a data frame generated, retrieves whether the MAC address in the source address field contained in the received data frame is contained in the proxy ARP table. That data frame is referred to as a proxy ARP request frame. More specifically, if the wireless LAN terminal device  20  moves from the side of the access point device  14  to the side of the access point device  16  of the handover destination, and the access point device  16  recognizes a connection with the wireless LAN terminal device  20 , a data frame is made so that the MAC address of the wireless LAN terminal device  20  is inserted in the source address and a broadcast address is inserted in the destination address field. The data frame thus made is broadcast to all ports, i.e. all access point devices. 
     In the case where the wireless LAN terminal device  20  is not in radio communications with the access point device  14 , the controller  42  receives a proxy ARP request frame through the network switcher  12 . The controller  42  determines by the retrieval functional block  42 E whether or not data corresponding to the MAC address, inserted in the source address field, in the proxy ARP request frame is present in the proxy ARP table  46 . The corresponding data is referred to as proxy ARP data. When the corresponding data is present in the proxy ARP table  46 , the controller  42  sends back the corresponding proxy ARP data by the proxy ARP functional block  42 B. 
     The deletion functional block  42 F implements a function which, when a reply is received at a handover source, determines that the wireless terminal device  20  is in connection with a handover destination, and deletes information stored in the proxy ARP table which corresponds to information whose completion of registration has been confirmed. If completion of registration is confirmed, it is determined that the handover is successful, and the controller  42  deletes the corresponding information which is old in the proxy ARP table  46  of the handover source. 
     The proxy ARP table  46  is memory, and is constructed to store proxy ARP data in which the MAC address in the source address field of the IP packet of the wireless LAN terminal device  20  in radio communication therewith is related to the IP address. Specifically, the proxy ARP table  46  stores a plurality of combined data in which an MAC address and a broadcast address are related to each other. In the proxy ARP table  46 , registration, retrieval, and deletion of data are controlled by the controller  42 . The wireless LAN interface  44  has the function of interfacing with a wireless LAN including wireless LAN terminal devices, or interfacing with radio  56 . 
     The wireless LAN terminal device  20  is a communication terminal device that enables a wireless network communication function. The wireless LAN terminal device  20  is connectable with the access point device  14 , for example, in an infrastructure mode of the networking method supported by the Institute of Electrical and Electronics Engineers (IEEE) 820.11 standard. The wireless LAN terminal device  20  can employ various terminal devices according to the manners in which wireless network communication is utilized. For instance, as a fixed terminal device, the wireless LAN terminal device  20  can employ a personal computer with a LAN board compatible with a wireless LAN function, a mobile IP telephone, wireless IP telephones including a soft phone, and so on. 
     It is to be noted that the wireless LAN terminal device  20  may be an existing terminal device. Because the internal configuration of the wireless LAN terminal device  20  does not form part of the present invention, a description of the internal construction will not be given. 
     Referring now to  FIG. 3 , there is exemplarily shown a proxy ARP request frame  58 . The proxy ARP request frame  58  contains a source address field  60 , a destination address field  62 , a type field  64 , a handover destination MAC address field  66 , and a frame check sequence (FCS) field  68 . Specifically, the source address field  60  includes the MAC address of the wireless LAN terminal device  20 . The destination address filed  62  includes a broadcast address (FF.FF.FF.FF.FF.FF in hexadecimal expression). In the type field  64 , information representing data type is stored. In the handover destination MAC address field  66 , the MAC address of the access point device  16  is stored. 
     Next, the operation after the handover in response to the wireless LAN terminal device  20  moving in the wireless communications system  10  will be described with reference to  FIG. 4 . 
     The wireless LAN terminal device  20  in radio communication with the access point device  14  moves into the administration area of the access point device  16  during communication. At this time, after the handover, the wireless LAN terminal device  20  sends a request for reconnection to the access point device  16  at time T 10  (CONNECTED 13 REQ  70 ). This connects the wireless LAN terminal device  20  to the access point device  16 . 
     Based on the information of the wireless LAN terminal device  20  handed over, the controller  50  in the access point device  16  generates a proxy ARP request frame in which the MAC address of the wireless LAN terminal device  20  is inserted in the source address field and a broadcast address is inserted in the destination address field. The access point device  16  transmits the proxy ARP request frame to the network switcher  12  through the wired-LAN interface  48  at time T 12  (PROXY_ARP_REQ  72 ). 
     The network switcher  12  receives the proxy ARP request frame in which the source address field is the MAC address of the wireless LAN terminal device  20 , through its physical port  26 . From this, the network switcher  12  recognizes that the wireless LAN terminal device  20  has been connected to the access point device  16 . In response to this recognition, at time T 14  the network switcher  12  updates the MAC address table  38  so that the physical port of the wireless LAN terminal device  20  is changed (UPDATE  74 ). In this manner, the physical port is replaced. 
     Next, the network switcher  12  sends the received proxy ARP request frame to all ports (all access point devices) (SEND  76 ). The access point devices  14  and  18  each receive the proxy ARP request frame and, based on the source address field in the proxy ARP request frame, reference the proxy ARP table  46  and proxy ARP table, not shown. The access point devices  14  and  18  each confirm the presence or absence of proxy ARP data that corresponds to the MAC address of the wireless LAN terminal device  20 . 
     In the access point device  14 , the proxy ARP data of the wireless LAN terminal device  20  is present because it is the handover source. In this case, the access point device  14  makes a data frame in which the destination address field is the access point device  16  and which contains the proxy ARP data of the wireless LAN terminal device  20 , and transmits the data frame to the network switcher  12  through its wired-LAN interface  40  at time T 18  (PROXY_ARP_DAT  78 ). On the other hand, in the access point device  18 , when the proxy ARP data of the wireless LAN terminal device  20  is not present, the received proxy ARP request frame is discarded. 
     The network switcher  12  receives the data frame having proxy ARP data  78  from the access point device  14 . Based on the destination address in the received data frame, the network switcher  12  transmits this data frame to the access point device  16  at time T 20  (PROXY_ARP_DAT  80 ). 
     The controller  50  in the access point device  16  receives proxy ARP data  80  and appends it to the proxy ARP table  54  at time T 22  (APPEND  82 ). After the network switcher  12  has transmitted the proxy ARP data  80  to the access point device  16 , the controller  42  in the access point device  14  transmits an ARP request  84  to the network switcher  12  through the wired-LAN interface  40  at time T 24  (ARP_REQ  84 ). The ARP request  84  to be generated in the controller  42  is generated using the proxy ARP function. The ARP request  84  is one which requests an MAC address corresponding to the IP address of the transmitted proxy ARP data  78 . 
     Referring now to  FIG. 5 , there is shown an ARP request  84 . The ARP request  84  contains a destination MAC address field  86 , a source MAC address field  88 , a source IP address field  90 , a source MAC address field  92 , a request destination IP address field  94 , and a request destination MAC address field  96 . These address fields are the same as general address fields. In the preferred embodiment, the destination MAC address  86  is set to a broadcast address (FF.FF.FF.FF.FF), the source MAC address  88  to the MAC address of the access point device  14 , the source IP address  90  to the IP address of the access point device  14 , the source MAC address  92  to the MAC address of the access point device  14 , the request destination IP address  94  to the IP address of the wireless LAN terminal device  20 , and the request destination MAC address  96  to zeros. 
     Returning  FIG. 4 , after receiving the ARP request  84  from the access point device  14 , the network switcher  12  transmits the received ARP request  84  to all ports (access point devices) as an ARP request  98  at time T 26  (ARP_REQ  98 ). In response to the ARP request from the access point device  14 , the controller  50  in the access point device  16  generates an ARP reply using the proxy ARP function and transmits the generated ARP reply  100  to the network switcher  12  through its wired-LAN interface  48  at time T 28  (ARP_REPLY  100 ). The ARP reply  100  is a packet which carries the MAC address of the wireless LAN terminal device  20  and in which the destination address is the access point device  14 . 
     After receiving the ARP reply  100  from the access point device  16 , the network switcher  12  transmits it to the access point device  14  as an ARP reply  102  at time T  30 , based on the destination address in the packet (ARP_REPLY  102 ). After receiving the ARP reply  102  supplied from the access point device  16 , the controller  42  in the access point device  14  determines that the handover of the proxy ARP data in the access point device  16  is successful (DETERMINE). When the handover is successful on the basis of the determination, the controller  42  deletes that proxy ARP data stored in the proxy ARP table  46  at time T 32  (DELETE  104 ). 
     According to the system configuration described above, immediately after the wireless LAN terminal device  20  has been handed over, if the access point device  16  transmits to the network switcher  12  a data frame in which the MAC address of the wireless LAN terminal device  20  is inserted in the source address field and a broadcast address is inserted in the destination address field, the MAC address table  38  of the network switcher  12  can be updated. This makes it possible to correctly relay a data frame addressed to the wireless LAN terminal device  20  received immediately after it has been handed over. 
     According to the preferred embodiment, the access point device  14  of the handover source can send back proxy ARP data in response to a proxy ARP frame received, and the access point device  16  of the handover destination can register the proxy ARP data received. More specifically, in the prior art, the access point device  16  could not execute the proxy ARP function unless it receives an IP packet from the wireless LAN terminal device  20  in radio communication therewith. According to the present invention, however, the access point device  16  is able to operate the proxy ARP function even when it does not receive an IP packet from the wireless LAN terminal device  20 . 
     Furthermore, the access point device  14  of the handover source confirms the movement of proxy ARP data to the handover destination using the proxy ARP function, and deletes old proxy ARP data. This can prevent the proxy ARP function from operating in the access point device  14 , resulting in the prevention of a network malfunction due to the malfunction of the proxy ARP function. 
     While the preferred embodiment is applied to the LAN which includes the network switcher  12  of one stage, the present invention is also applicable to a LAN which includes network switchers of multiple stages, as shown in  FIG. 6 . For example, even in the case of a multiple-stage configuration comprising a first stage network switcher  12  and a second stage network switcher  106 , a data frame in which a broadcast address is incorporated in the destination address field is transmitted, so that MAC address tables  38  and  108  in all the network switchers  12  and  106  can be updated. In the multiple-stage configuration, the physical port  30  of the first stage network switcher  12  and the physical port  110  of the second stage network switcher  106  are connected together by a signal line  112 . 
     While the present invention has been described with reference to the particular illustrative embodiments, the invention is not to be restricted to the embodiments. For example, the number of network switchers, the number of network switcher ports, the number of access point devices, and the number of wireless LAN terminal devices in the communications system of the present invention are not limited to the embodiments. 
     The entire disclosure of Japanese patent application No. 2005-314810 filed on Oct. 28, 2005, including the specification, claims, accompanying drawings and abstract of the disclosure is incorporated herein by reference in its entirety. 
     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.