Abstract:
Each access point determines the LAN cable insertion status and acts as the master access point if a cable is inserted, or as the slave access point if no cable is connected. Of the two access points receiving a “connection instruction,” the master access point or a upper access point connected directly or indirectly to the master access point sends a “connection advice message” from the higher level, the lower access point not connected to the master access point sends a “connection request message” from the lower level, and then a “connection response message” is sent from the higher level, and through this procedure the lower access point is added to a new service area.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a wireless LAN system used for extending the communication area and increasing the handover speed.  
         [0003]     2. Description of the Related Art  
         [0004]     To extend the communication area of a local area network (LAN), a wireless LAN access point is installed in the current communication area as well as in the new area to establish communication with. Then, by setting the MAC address of each access point in the other access point, communication between the two access points via a wireless LAN becomes possible. When a mobile station is installed in the new communication area and registered to the access point in the new area, the mobile station can communicate with the current communication area via the two access points ( FIG. 1 ). This method using a wireless LAN is generally referred to as the access point interconnection system or WDS (Wireless Distribution System) (refer to IEEE Standard 802.11, 1999 Edition).  
       SUMMARY OF THE INVENTION  
       [0005]     When a wireless LAN is used, there is no risk of LAN cables increasing to make the network configuration complex. However, the settings required in the introduction stage are cumbersome and give significant burdens to the installation manager.  
         [0006]     Additionally, allowing multiple access points to interconnect with one other forms loops in the network, which interferes with the determination of unique communication paths. To prevent loops from forming, a technology called spanning tree must be incorporated into the network equipment. However, this technology sends information packets into the network on a regular basis and thereby consumes the bandwidth of the wireless LAN network.  
         [0007]     If multiple access points are installed and mobile stations are provided to move between the access points (handover), information regarding the mobile stations as well as security information must be set in all access points. A method to centrally control the mobile stations is available, but it requires a new server to be installed in the network independent of the access points.  
         [0008]     Also, a mobile station performs registration processing (handover processing) at each new access point to which it moves, so movement of the mobile station during communication may temporarily disconnect the communication.  
         [0009]     The present invention realizes a wireless LAN area extension method that can extend the service area through a simple procedure by solving these drawbacks associated with the conventional technologies.  
         [0010]     To solve the above problems, the present invention utilizes the functions specified below.  
         [0000]     (Means 1) Starting of Access Point Interconnection  
         [0011]     Each access point automatically initiates an access point interconnection operation upon detection of a change in the environment such as pressing of the connection instruction button, sending of a connection instruction message, input of power or other external “connection instruction,” stopping of the connection destination access point or connection of a cable, to realize simple area extension ( FIG. 2 ( a )).  
         [0000]     (Means 2) Automation of Access Point Interconnection  
         [0012]     In the present invention, each access point determines the LAN cable insertion status and acts as the master access point if a cable is inserted, or as the slave access point if no cable is connected.  
         [0013]     Of the two access points receiving a “connection instruction,” the master access point or a upper access point connected directly or indirectly to the master access point sends a “connection advice message” ( FIG. 2 ( b )). Of the two access points receiving a “connection instruction,” the lower access point not connected to the master access point receives the connection advice message and then sends a “connection request message” to the access point sending the “connection advice message” ( FIG. 2 ( c )). The upper access point receiving the “connection request message” notifies a “connection response message” to the lower access point ( FIG. 2 ( c )). Each of the two access points sets the other access point as its connection destination. Furthermore, the upper access point notifies other access point in the network of the addition of a new access point ( FIG. 2 ( d )). The above procedure is automated to reduce the workload of the person installing access points and thereby realize a function for simple area extension.  
         [0000]     (Means 3) Limitation of Candidate Connection Destination Access Points  
         [0014]     Each access point retains, as the connection relationship information of an access point directly or indirectly connected to itself, the MAC address, hop number, station MAC address and other information regarding that access point. The hop number is 1 for the master access point, 2 for the slave access point connected to the master access point, 3 for the slave access point connected to the slave access point with hop number 2, and increases to 4, 5, . . . , thereafter in the same manner.  
         [0015]     At the upper access point receiving a “connection request message,” judgment of whether the connection is to be permitted or refused is made using the connection relationship information. For example, the access point references its connection relationship information and if the hop number from the master access number is equal to or greater than the set value, it refuses connection with the lower access point sending the “connection request message” ( FIG. 3 ). Alternatively, the access point references its connection relationship information and if the number of lower access points already connected to itself exceeds the set value, it refuses connection with the access point sending the “connection request message” ( FIG. 4 ).  
         [0016]     As explained above, automatic connection permission/refusal judgment prevents loads from concentrating on a certain access point and at the same time reduces the workload of the person installing access points.  
         [0000]     (Means 4) Prevention of Network Loops  
         [0017]     The connection relationship information of each access point is investigated and if a loop will be formed in the network as a result of connecting the access point issuing a “connection request message,” the connection is refused or the loop connection is deleted ( FIG. 5 ).  
         [0018]     The above automatically realizes connection among access points with one master access point set as the base and multiple slave access points arranged in a tree shape, thereby preventing loops from forming. As a result, the spanning tree function becomes no longer necessary.  
         [0000]     (Means 5) Automatic Selection of Connection Destination Access Point  
         [0019]     A “connection instruction” is issued to multiple access points ( FIG. 6 ). Of the multiple access points receiving the “connection instruction,” the master access point or an upper access point connected directly or indirectly to the master access point sends a “connection advice message.” Of the multiple access points receiving the “connection instruction,” a lower access point not connected to the master access point receives the “connection advice message ( FIG. 7 ).  
         [0020]     The lower access point receiving the “connection advice messages” sent from multiple access points references the connection relationship information included in each “connection request message,” selects the access point to become its connection destination, and then notifies a “connection request message” to the selected access point ( FIG. 8 ). The access point receiving the “connection request message” from the lower access point sends a “connection response message” ( FIG. 9 ). At the same time, each of these two access points sets the other access point as its connection destination. Thereafter, each access point updates the connection relationship information held by itself and sends the new connection relationship information to other access point in the group. The access point in the group receiving the new connection relationship information updates the connection relationship information held by itself ( FIG. 10 ).  
         [0021]     If a connection destination access point is to be selected, (Means 3) can be used to limit the candidate connection destination access points. Also, the total number of access points in the connection relationship information can be used to select connection to a tree having a fewer number of access points ( FIG. 11 ). Also, the hop number can be used to select an access point closer to the master access point ( FIG. 12 ). Also, the number of lower access points can be used to connect to an access point having a fewer number of lower access points ( FIG. 13 ).  
         [0022]     Furthermore, the hop number can be used to select an access point farther away from the master access point. Alternatively, (Means 3) can be used to limit the number of lower access points to 1 and thereby prevent branching of the tree ( FIG. 14 ). These methods allow for automatic identification of and connection to an access point appropriate as the connection destination to realize simple area extension.  
         [0000]     (Means 6) Central Station Control  
         [0023]     When a station sends a “registration request message” to a slave access point, the slave access point uses its own function to transfer the “registration request message” to the master access point. The master access point determines if the station can be registered, and then transfers a permission or refusal response to the slave access point via a “registration response message,” and the slave access point notifies the “registration response message” to the station ( FIG. 15 ).  
         [0024]     If the station sends a “registration request message” to the master access point, normal station registration processing is performed in accordance with the IEEE802.11 standard.  
         [0025]     Through the above operations, the stations are centrally controlled by the master access point to simplify the station control.  
         [0000]     (Means 7) Distribution of Station Information  
         [0026]     When registration of a station is permitted via the aforementioned central station control or station registration processing in accordance with the IEEE802.11 standard, the access point connecting to the station notifies other access point of the registration of the station. The notified access point then updates the connection relationship information held by itself and also transfers the notification to other access point. The access point connected to the station may notify the connection relationship information held by itself to the station ( FIG. 16 ).  
         [0027]     Through the above operations, station information can be shared within the same tree for use in packet transfer or reduction of handover time.  
         [0000]     (Means 8) High-Speed Handover  
         [0028]     If an access point exists that offers a better communication environment than the access point currently connected, the station may change the connection destination access point (handover). Determination of the handover destination is implemented by means of comparison of the beacon information sent by each access point (passive probing), comparison of probe response information returned to a probe request (active probing), and so on.  
         [0029]     As shown in  FIG. 17 , the station determines the access point to become the handover destination based on beacon information (or probe response information). The station sends a data packet to the handover destination access point. The access point receiving the data packet references the connection relationship information held by itself and if the station is registered, changes the connection relationship information, sends a “movement notification message” for the station to other access point, and then transfers the data packet sent from the station. The access point receiving the data packet references the connection relationship information held by itself and if the station is not registered, sends a “movement refusal message” to the station.  
         [0030]     Upon receiving the “movement notification message,” other access point updates the connection relationship information and changes the transfer destination access point for the message addressed to the station.  
         [0031]     When handing over to an access point not registered in the connection relationship information held by itself or access point from which a movement refusal has been notified, the station performs handover processing in accordance with the IEEE802.11 standard.  
         [0000]     (Means 9) Data Packet Transfer Processing  
         [0032]     As shown in  FIG. 18 , after receiving a message not addressed to itself the access point transfers the message to other access point or station connected to itself. At this time, the access point references the connection relationship information held by itself and determines the transfer destination of the message or destroys the message.  
         [0033]     The present invention allows for extension of the service area of a wireless LAN through a simple procedure, thereby providing a very effective means for building an economical, easy-to-use wireless LAN. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]      FIG. 1  is a block diagram for explaining the procedure of communication area extension in a wireless LAN;  
         [0035]      FIG. 2  is a layout drawing for explaining the procedure of access point connection in the present invention;  
         [0036]      FIG. 3  is a layout drawing for explaining the hop number used to limit the access point connection in the present invention;  
         [0037]      FIG. 4  is a layout drawing for explaining the lower access number used to limit the access point connection in the present invention;  
         [0038]      FIG. 5  is a layout drawing for explaining the loop limitation in access point connection in the present invention;  
         [0039]      FIG. 6  is a layout drawing for explaining the initiation request for access point connection in the present invention;  
         [0040]      FIG. 7  is a layout drawing for explaining the information advice at access point connection in the present invention;  
         [0041]      FIG. 8  is a layout drawing for explaining the selection of connection destination and sending of connection request at access point connection in the present invention;  
         [0042]      FIG. 9  is a layout drawing for explaining the connection judgment and sending of connection permission at access point connection in the present invention;  
         [0043]      FIG. 10  is a layout drawing for explaining the connection setting and updating of connection relationship information at access point connection in the present invention;  
         [0044]      FIG. 11  is a layout drawing for explaining the selection based on total number of access points at access point connection in the present invention;  
         [0045]      FIG. 12  is a layout drawing for explaining the selection based on hop number at access point connection in the present invention;  
         [0046]      FIG. 13  is a layout drawing for explaining the selection based on number of lower access points at access point connection in the present invention;  
         [0047]      FIG. 14  is a layout drawing for explaining a non-branching configuration when implementing access point connection in the present invention;  
         [0048]      FIG. 15  is a layout drawing for explaining the station registration at access point connection in the present invention;  
         [0049]      FIG. 16  is a layout drawing for explaining the notification and updating of connection relationship information at access point connection in the present invention;  
         [0050]      FIG. 17  is a layout drawing for explaining the high-speed handover at access point connection in the present invention;  
         [0051]      FIG. 18  is a layout drawing for explaining the packet transfer in a wireless LAN based on the present invention;  
         [0052]      FIG. 19  is a block diagram showing an example of access point configuration used in the present invention;  
         [0053]      FIG. 20  is a layout drawing showing a network configuration before connection of an access point (AP 5 ) in the present invention;  
         [0054]      FIG. 21  is a drawing showing an example of access point connection sequence in the present invention;  
         [0055]      FIG. 22  is a flowchart showing the access point connection operation in the present invention;  
         [0056]      FIG. 23  is a layout drawing showing a network configuration after connection of an access point (AP 5 ) in the present invention;  
         [0057]      FIG. 24  is a layout drawing showing a network configuration before movement of an access point (AP 6 ) in the present invention;  
         [0058]      FIG. 25  is a drawing showing an example of sequence for selecting the connection destination from multiple access points in the present invention;  
         [0059]      FIG. 26  is a flowchart showing the connection operation upon reception of an advice instruction packet (b) and pressing of the connection instruction switch (a) at an access point in the present invention;  
         [0060]      FIG. 27  is a flowchart showing the operation of upper access point selection in the present invention;  
         [0061]      FIG. 28  is a layout drawing showing a network configuration after movement of an access point (AP 6 ) in the present invention;  
         [0062]      FIG. 29  is a layout drawing for explaining the station registration in the present invention;  
         [0063]      FIG. 30  is a drawing showing an example of station registration sequence in the present invention;  
         [0064]      FIG. 31  is a layout drawing for explaining the packet transfer in a wireless LAN based on the present invention;  
         [0065]      FIG. 32  is a drawing showing an operation sequence of the packet transfer illustrated in  FIG. 31 ;  
         [0066]      FIG. 33  is a block diagram showing an example of station supporting high-speed handover in the present invention;  
         [0067]      FIG. 34  is a drawing showing an example of handover sequence in the present invention; and  
         [0068]      FIG. 35  is a layout drawing showing an example of network for explaining the handover in the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0069]      FIG. 19  shows a block diagram of an access point in which the aforementioned functions are installed. The access point comprises the access point control unit ( 4 ), memory ( 5 ), send/receive unit ( 2 ), wireless LAN port ( 1 ), wired LAN port ( 3 ) and switch ( 6 ). The wireless LAN port ( 1 ) receives the packets sent to the wireless LAN network and sends the packets from the send/receive unit to the wireless LAN network. The wired LAN port ( 3 ) receives the packets sent to the wired network and sends the packets from the send/receive unit to the wired network. The send/receive unit ( 2 ) transfers to the wireless LAN port ( 1 )/wired LAN port ( 3 ) or access point control unit ( 4 ), in accordance with the instruction by the access point control unit ( 4 ), the packets transferred from the access point control unit ( 4 ) or wireless LAN port ( 1 )/wired LAN port ( 3 ). The access point control unit ( 4 ) references the “connection relationship information” in the memory ( 5 ) and performs connection control of other access points, controls station registration and handover (station movement) and instructs packet transfer. It also updates the “connection relationship information.” 
         [0000]     (Access Point Interconnection Function)  
         [0000]     (Example of One-to-One Access Point Connection)  
         [0070]     As shown in  FIG. 20 , an example where new access point AP 5  is connected to access point AP 3  in a network that already has access points AP 1 , AP 2 , AP 3  and AP 4  is used to explain the access point interconnection operation.  
         [0071]     Each access point has the configuration shown in  FIG. 19 . The memory ( 5 ) of each access point stores the “connection relationship information” specified in each line of Table 1. The MAC column of Table 1 stores the MAC address of each access point. The hop column stores the hop number from the master access point. The higher MAC column stores the MAC address of the upper access point connected to the applicable access point. The lower number column stores the number of lower access points connected to the applicable access point. The lower MAC column stores the MAC address of each lower access point connected to the applicable access point.  
                                                                       TABLE 1                           Connection Relationship Information in Each Access Point       before Connection of AP5                        Higher   Lower               MAC   Hop   MAC   number   Lower MAC                        Connection   ADR1   1   —   2   ADR2   ADR3       relationship       information in       AP1&#39;s memory       Connection   ADR2   2   ADR1   0   —   —       relationship       information in       AP2&#39;s memory       Connection   ADR3   2   ADR1   1   ADR4       relationship       information in       AP3&#39;s memory       Connection   ADR4   3   ADR3   0   —   —       relationship       information in       AP4&#39;s memory       Connection   ADR5   —   —   0   —   —       relationship       information in       AP5&#39;s memory                  
 
         [0072]      FIG. 21  shows a messaging sequence between access points, while  FIG. 22  shows the operation of the access point connection function ( 4 - 1 ). If AP 5  is to be connected as the lower access point of AP 3 , the connection instruction switch ( 6 ) is pressed on both AP 3  and AP 5 . When the switch ( 6 ) is pressed, the access point connection function ( 4 - 1 ) in the access point control unit ( 4 ) is activated.  
         [0073]     The access point connection function ( 4 - 1 ) in AP 3  references the connection relationship information in the memory ( 5 ) and detects that it is already connected to a upper access point, and then instructs the send/receive unit ( 2 ) to send a “connection advice packet” including its own MAC address (ADR3) at a constant frequency during a predetermined time (T seconds). According to the instruction, the send/receive unit ( 2 ) sends a “connection advice packet” via the wireless LAN port and waits for a “connection request packet” from AP 5 .  
         [0074]     The access point connection function ( 4 - 1 ) in AP 5  references the connection relationship information in the memory ( 5 ) and detects that it is not already connected to an upper access point, and then instructs the send/receive unit ( 2 ) to receive a “connection advice packet” during a predetermined time (T seconds). After being notified of the reception of a “connection advice packet” from the send/receive unit ( 2 ), the access point connection function ( 4 - 1 ) in AP 5  instructs the send/receive unit ( 2 ) to send a “connection request packet” to the MAC address included in the packet.  
         [0075]     After receiving the “connection request packet” from AP 5 , the access point connection function ( 4 - 1 ) in AP 3  checks its hop number and lower number in the “connection relationship information” in the memory ( 5 ) and if the values are equal to or below the respective thresholds, instructs the send/receive unit ( 2 ) to send a “connection permission packet.” If the values exceed the respective thresholds, the access point connection function ( 4 - 1 ) in AP 3  instructs sending a “connection refusal packet.” If the access point connection function ( 4 - 1 ) in AP 3  instructs sending a “connection permission packet,” it then connects AP 5  as the lower access point.  
         [0076]     After being notified of the reception of a “connection permission packet” from the send/receive unit ( 2 ), the access point connection function ( 4 - 1 ) in AP 5  connects AP 4  as the upper access point.  
         [0077]     Finally, the access point connection function ( 4 - 1 ) in AP 3  updates the “connection relationship information” in the memory ( 5 ) and instructs the send/receive unit ( 2 ) to send a “connection notification packet” to the MAC addresses of higher and lower access points stored in the “connection relationship information” in order to notify the connection of AP 5 .  
         [0078]     The access point control unit ( 4 ) of the access point receiving the “connection notification packet” updates the “connection relationship information” in the memory ( 5 ) and instructs the send/receive unit ( 2 ) to send the “connection notification packet” to the MAC addresses of higher and lower access points stored in the “connection relationship information” (excluding the address from which the “connection notification packet” was received).  
         [0079]      FIG. 22  shows a flow of connection operation that takes place at the access point. Each operation step is explained below. 
    S 0 : The access point initiates connection operation when the switch is pressed.     S 1 : The access point references the “connection relationship information” to check if its hop number is registered.     S 2 : If the hop number is not yet registered, the access point performs a “connection advice packet” receive operation to connect as the lower access point.     S 3 : When a “connection advice packet” is received, the access point sends a “connection request packet.”    S 4 : The access point waits for reception of a “connection permission packet.” If a “connection refusal packet” is received or “connection permission packet” cannot be received within a specified time, the access point ends the processing (S 14 ).     S 5 : When a “connection permission packet” is received, the access point performs “connection setting.”    S 6 : If the hop number is registered in S 1 , the access point performs a “connection advice packet” send operation to connect as the upper access point.     S 7 : The access point waits for reception of a “connection request packet.”    S 8 : When a “connection request packet” is received, the access point investigates the “connection relationship information.”    S 9 : The access point determines if accommodation is permitted based on the investigation result of the “connection relationship information.”    S 10 : If accommodation is permitted, the access point performs “connection setting.”    S 11 : The access point sends a “connection permission packet” to the sender of the “connection request packet.”    S 12 : The access point sends a “connection notification packet” to the connection destination access point to notify the connection of a new access point, and then ends the processing (S 14 ).     S 13 : If accommodation is refused, the access point sends a “connection refusal packet” to the sender of the “connection request packet,” and then ends the processing.     S 14 : End      
         [0095]      FIG. 23  shows the network configuration after connection of AP 5 . Table 2 lists the “connection relationship information” in the memory ( 5 ) of each access point after connection of AP 5 .  
                                                                       TABLE 2                           Connection Relationship Information in Each Access Point       after Connection of AP5                        Higher   Lower               MAC   Hop   MAC   number   Lower MAC                        Connection   ADR1   1   —   2   ADR2   ADR3       relationship       information in       AP1&#39;s memory       Connection   ADR2   2   ADR1   0   —   —       relationship       information in       AP2&#39;s memory       Connection   ADR3   2   ADR1   2   ADR4   ADR5       relationship       information in       AP3&#39;s memory       Connection   ADR4   3   ADR3   0   —   —       relationship       information in       AP4&#39;s memory       Connection   ADR5   3   ADR3   0   —   —       relationship       information in       AP5&#39;s memory                    
 (Example of Many-to-One Access Point Connection) 
 
         [0096]     As shown in  FIG. 24 , AP 6  is connected to AP 5  as the lower access point in a network that has access points AP 1  to AP 6 . Here, an example where AP 6  is moved and connected as the lower access point of one of AP 1  to AP 5 , whichever offers a better communication environment, is used to explain the access point interconnection operation.  
         [0097]     Each access point has the configuration shown in  FIG. 19 . The memory ( 5 ) of each access point in the group where AP 1  is the master access point stores the same “connection relationship information” specified in Table 3. The memory ( 5 ) of each access point in the group where AP 5  is the master access point stores the same “connection relationship information” specified in Table 4. Here, the MAC address column stores the MAC addresses of all access points in the applicable group. The higher MAC column stores the MAC address of the upper access point connected to the access point having each address in the MAC address column. The hop column stores the hop number of the access point having each address in the MAC address column.  
                                 TABLE 3                           Connection Relationship Information of Group Having AP1 as       Master Access Point before Movement of AP6                MAC address   Higher MAC   Hop                       ADR1   —   1           ADR2   ADR1   2           ADR3   ADR1   2           ADR4   ADR3   3                      
 
         [0098]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                   
               
               
                 Connection Relationship Information of Group Having AP5 as 
               
               
                 Master Access Point before Movement of AP6 
               
             
          
           
               
                   
                 MAC address 
                 Higher MAC 
                 Hop 
               
               
                   
                   
               
               
                   
                 ADR5 
                 — 
                 1 
               
               
                   
                 ADR6 
                 ADR5 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0099]      FIG. 25  shows a messaging sequence between access points, while  FIG. 26  illustrates the operation at the access point. An “advice instruction packet” is sent from the PC via the wired network to accommodate AP 6 . After being informed of the reception of an advice instruction packet from the send/receive unit ( 2 ), the access point connection functions of maser access point AP 1  and AP 5  instruct the send/receive unit ( 2 ) to transfer the “advice instruction packet” to the lower access point. After being informed of the reception of an “advice instruction packet” from the send/receive unit ( 2 ), the access point connection function ( 4 - 1 ) in the slave access point instructs the send/receive unit ( 2 ) to transfer the “advice instruction packet” to the lower access point. The connection switch ( 6 ) is pressed on AP 6  to select the connection destination.  
         [0100]     After being informed of the reception of an “advice instruction packet” from the send/receive unit ( 2 ), the access point connection functions ( 4 - 1 ) in AP 1  to AP 5  issue an instruction to the send/receive unit ( 2 ) to send a “connection advice packet” repeatedly for a specified time (T seconds). The send/receive unit ( 2 ) sends a “connection advice packet” to the wireless LAN port.  
         [0101]     The “connection advice packet” stores the information shown in Table 5, which was created from the connection relationship information. “MAC” indicates the MAC address of the access point sending the “advice packet.” “Hop” indicates the hop number of the access point sending the “advice packet.” “Lower number” indicates the number of lower access points connected to the access point sending the “advice packet.” “H1” indicates the total number of access points under the access point having hop number 1. “H2” indicates the total number of access points under the access point having hop number 2, being located between the master access point and the applicable access point. Similarly, “H3” indicates the total number of access points under the access point having hop number 3, being located between the master access point and the applicable access point. As an example, line 2 in Table 5 shows the content of the “connection advice packet” sent from access point AP 2 . It indicates that the MAC address of AP 2  is ADR2 and the hop number of AP 2  is 2. The lower number column shows that the number of lower access points for AP 2  is 0. The H1 column indicates that the total number of access points under master access point AP 1  is 3, while the H2 column indicates that the total number of access points under slave access point AP 2  is 0. Since AP 2  has hop number 2, it does not have any H3 information.  
                                                                           TABLE 5                           Content of Connection Advice Packet                        Lower                       MAC   Hop   number   H1   H2   H3                        Advice information   ADR1   1   2   3               sent from AP1       Advice information   ADR2   2   0   3   0       sent from AP2       Advice information   ADR3   2   1   3   1       sent from AP3       Advice information   ADR4   3   0   3   1   0       sent from AP4       Advice information   ADR5   1   1   1       sent from AP5                  
 
         [0102]      FIG. 26  shows a flow of connection operation that takes place at the access point. Each operation step is explained below.  
         [0103]     (a) Press the connection instruction switch 
    S 20 : When the switch is pressed, the access point initiates connection operation.     S 21 : The access point performs a “connection advice packet” receive operation.     S 22 : The access point selects the connection destination access point according to the flowchart in  FIG. 27  provided later.     S 23 : The access point sends a “connection request packet” to the selected access point.     S 24 : The access point waits for reception of a “connection permission packet.” If a “connection refusal packet” is received or “connection permission packet” cannot be received within a specified time, the access point ends the processing.     S 25 : When a “connection permission packet” is received, the access point updates the “connection relationship information” (connection setting).     S 26 : End    
 
         [0111]     (b) Receive an advice instruction packet 
    S 30 : The access point receiving an “advice instruction packet” initiates connection operation.     S 31 : The access point sends a “connection advice packet” for a specified time, while performing a “connection request packet” receive operation at the same time.     S 32 : The access point checks if a “connection request packet” was received from multiple access points.     S 33 : If a “connection request packet” was received only from one access point, the access point investigates the “connection relationship information.”    S 34 : The access point determines if accommodation is permitted based on the investigation result of the “connection relationship information.”    S 35 : If accommodation is permitted, the access point sends a “connection permission packet.”    S 36 : The access point sends a “connection notification packet” to the connection destination access point to notify the connection of a new access point.     S 37 : The access point updates the “connection relationship information” (connection setting) to end the processing.     S 38 : If it determines that a “connection request packet” was received from multiple access points based on the check result in S 32 , or that accommodation is not permitted as a result of S 34 , the access point sends a “connection refusal packet.”    S 39 : End    
 
         [0122]      FIG. 27  shows an upper access point selection flow. Each operation step is explained below. 
    S 41 : The access point excludes from the candidates those access points from which a “connection advice packet” was received in S 21  whose signal intensity is equal to or below the threshold.     S 42 : The access point excludes from the candidates those access points from which a “connection advice packet” was received in S 21  whose hop number is equal to or above the threshold.     S 43 : The access point excludes from the candidates those access points from which a “connection advice packet” was received in S 21  whose number of lower access points is equal to or above the threshold.     S 44 : The access point checks if a candidate access point exists as a result of S 41  to S 43 .     S 46 : If no candidate exists, the access point determines whether or not to change any of the thresholds.     S 47 : If the thresholds are not changed, the access point ends the processing.     S 45 : If any of the thresholds was changed, the access point returns to S 41  and selects again.     S 48 : If a candidate access point exists in S 44 , the access point sets the investigation hop to 1.     S 49 : The “connection advice packet” from each access point records the hop number of the access point sending the “connection advice packet,” the number of lower access points directly connected to the access point sending the “connection advice packet” (lower number), and the total number of lower access points directly or indirectly connected to the access points having hop numbers 1 to 3 being located between the applicable access point and master access point (H1: hop 1, H2: hop 2, H3: hop 3), as shown in each line of Table 5. Of the candidate access points, the “connection advice packet” sender access point having the least number of total lower access points (number of access points indirectly accommodated), as revealed by the investigation hop, is selected as the candidate (there may be more than one candidate), and other access points are excluded.     S 50 : The access point compares the investigation hop and the hop column in Table 5 and checks if any access point equivalent to the investigation hop exists (there may be more than one such access point).     S 51 : If no access point exists that has the investigation hop, the “connection advice packet” sender access point selected as the candidate in S 49  is an access point connected at a lower position than the investigation hop. Therefore, the access point increases the investigation hop number by 1 and repeats S 49 .     S 52 : If an access point having the investigation hop exists as a result of S 50 , this access point is located closer to the master access point (hop 1) connected to the wired LAN network and has a fewer number of total lower access points connected directly or indirectly. Therefore, such access point is subject to less traffic and therefore suitable as the connection destination access point. 
 
 The access point selects as the candidate the access point having the smallest number of access points directly accommodated (lower number in Table 5) from all such access points (there may be more than one candidate). 
    S 53 : The access point investigates if there are multiple candidate access points.     S 54 : If there is only one access point, the access point selects it as the connection destination and proceeds to S 56 .     S 55 : If there are multiple candidate access points, the access point selects the one with the greatest signal intensity, and then proceeds to S 56 .      
         [0138]     After elapse of T seconds, the access point connection function ( 4 - 1 ) of AP 6  determines the connection destination using the information in the “information advice packet” received by the send/receive unit ( 2 ), and instructs the send/receive unit ( 2 ) to send a “connection request packet.” In the example, it is assumed that “information advice packets” are received from nearby access points AP 2 , AP 3  and AP 4 , and that AP 2  is selected according to the flowchart in  FIG. 27 , as shown in  FIG. 28 .  
         [0139]     The access point connection function ( 4 - 1 ) of AP 2  is notified of the reception of a “connection request packet” from the send/receive unit ( 2 ), and checks its hop number and number of connected lower access points in the memory. If they are equal to or below the specified values, the access point connection function ( 4 - 1 ) of AP 2  instructs the send/receive unit ( 2 ) to send a “connection permission packet.” 
         [0140]     When notified of the reception of a “connection permission packet” from the send/receive unit ( 2 ), the access point control unit ( 4 ) of AP 6  sets the MAC address of AP 2  as the MAC address of upper access point. The access point control unit ( 4 ) of AP 2  updates the “connection relationship information,” and then notifies the new “connection relationship information” to the MAC addresses of higher and lower access points. The new “connection relationship information” is shown in Tables 6 and 7.  
                                 TABLE 6                           Connection Relationship Information of AP1 Group after       Movement of AP6                MAC address   Higher MAC   Hop                       ADR1   —   1           ADR2   ADR1   2           ADR3   ADR1   2           ADR4   ADR3   3           ADR6   ADR2   3                      
 
         [0141]                                      TABLE 7                           Connection Relationship Information of AP5 Group after       Movement of AP6                MAC address   Higher MAC   Hop                       ADR5   —   1                        
 (Station Connection Function) 
 
         [0142]     A station must be registered to the access point first in order to establish communication. An example where station STA 1  is registered via access point AP 6 , as shown in  FIG. 29 , is explained.  
         [0143]      FIG. 30  shows a messaging sequence between access points at the time of station registration. First, station STA 1  broadcasts a probe request (P request). When informed of the reception of a probe request from the send/receive unit ( 2 ), the station registration processing function of the access point instructs the send/receive unit ( 2 ) to send a probe response (P response). In  FIG. 30 , AP 2  and AP 6  receive a probe request and send a probe response.  
         [0144]     After receiving the probe response, station STA 1  selects, from among the access points that sent a probe response (AP 2 , AP 6 ), AP 6  as an appropriate access point to communicate with, and then sends an authentication request (Au request).  
         [0145]     When informed of the reception of an authentication request from the send/receive unit ( 2 ), the station registration processing function ( 4 - 2 ) of access point AP 6  searches the connection relationship information and instructs the send/receive unit ( 2 ) to transfer the authentication request to upper access point AP 2 .  
         [0146]     Similarly, when informed of the reception of an authentication request from the send/receive unit ( 2 ), the station registration processing function ( 4 - 2 ) of access point AP 2  searches the connection relationship information and instructs the send/receive unit ( 2 ) to transfer the authentication request to upper access point AP 1 .  
         [0147]     When informed of the reception of an authentication request from the send/receive unit ( 2 ), the station registration processing function ( 4 - 2 ) of access point AP 1  instructs the send/receive unit ( 2 ) to transfer the authentication response (Au response) to lower access point AP 2 .  
         [0148]     When informed of the reception of an authentication response from the send/receive unit ( 2 ), the station registration processing function ( 4 - 2 ) of access point AP 2  instructs the send/receive unit ( 2 ) to transfer the authentication response to lower access point AP 6 .  
         [0149]     When informed of the reception of an authentication response from the send/receive unit ( 2 ), the station registration processing function ( 4 - 2 ) of access point AP 6  instructs the send/receive unit ( 2 ) to transfer the authentication response to station STA 1 .  
         [0150]     After receiving the authentication response, station STA 1  sends an association request (As request) to access point AP 6 . This request is also transferred to access point AP 1 , and an association response (As response) is returned from access point AP 1 .  
         [0151]     The station registration processing function ( 4 - 2 ) of access point AP 6  registers station STA 1  in the connection relationship information in the memory. At the same time, access point AP 6  sends a registration of station STA 1  to access point AP 2 , and access point AP 2  sends it to access point AP 1 . Each access point thus registers the station information. AP 6  also sends the connection relationship information (Table 6) to station STA 2 .  
         [0152]     Table 8 shows an example of station information registration in the connection relationship information of access point AP 6 . The access point MAC column indicates the MAC address of the applicable access point as well as the MAC addresses of higher/lower access points. Here, the MAC address of access point AP 6  (ADR6) and that of AP 2  (ADR2) being the upper access point of AP 6  are stored. The station MAC address column stores the MAC address of each station registered in the group. Here, the address of station STA 1  (ADRS1) is stored in the MAC address line of ADR6 corresponding to access point AP 6 .  
                             TABLE 8                           Station Information in AP6                Access point   Station           MAC   MAC                       ADR2               ADR6   ADRS1                      
 
         [0153]     Table 9 shows the connection relationship information (station information) of access point AP 1 . The access point MAC column shows the MAC address of access point AP 1  (ADR1) and those of AP 2  (ADR2) and AP 3  (ADR3) being the lower access points of AP 1 . The station MAC address column stores the address of station STA 1  in the MAC address line of ADR2 corresponding to access point AP 2 , indicating that packets addressed to STA1 will be transferred to AP 2 . Similarly, Table 10 shows the connection relationship information (station information) of access point AP 3 .  
                             TABLE 9                           Station Information in AP1                Access point   Station           MAC   MAC                       ADR1               ADR2   STA1           ADR3                      
 
         [0154]                                  TABLE 10                           Station Information in AP3                Access point   Station           MAC   MAC                       ADR1   STA1           ADR3           ADR4                        
 (STA Handover Processing) 
 
         [0155]     The access point references the connection relationship information and performs high-speed handover processing.  FIG. 33  shows a block diagram of a station supporting high-speed handover processing. The station comprises the station control unit ( 14 ), memory ( 15 ), send/receive unit ( 12 ), wireless LAN port ( 11 ) and application ( 13 ).  
         [0156]     The wireless LAN port ( 11 ) receives packets sent to the wireless LAN network and sends the packets from the send/receive unit to the wireless LAN network. The application ( 13 ) provides the voice communication function and other functions that use a wireless LAN to send/receive data. The send/receive unit ( 12 ) transfers to the wireless LAN port ( 11 )/application ( 13 ) or station control unit ( 14 ), according to the instruction by the station control unit ( 14 ), the packets transferred from the station control unit ( 14 ) or wireless LAN port ( 11 )/application ( 13 ). The station control unit ( 14 ) references the “connection relationship information” in the memory ( 15 ) and controls handover (station movement).  
         [0157]     As shown in  FIG. 35 , a case where station STA connected to AP 6  performs handover is explained. When notified from the send/receive unit ( 12 ) of the reception of a beacon sent from an access point (AP 1  to AP 6 ) operating in the same channel, the handover request function ( 14 - 2 ) of station STA 1  retrieves the MAC address (ADR1 to ADR6) and communication environment information (signal intensity and SN ratio) of the beacon sender and retains the information in the memory ( 15 ).  
         [0158]      FIG. 34  shows a handover sequence. The handover request function ( 14 - 2 ) of station STA 1  tabulates the communication environment information during a specified period and upon finding access point AP 3  a more appropriate communication target than the currently communicating access point AP 6 , it compares the MAC address of AP 3  (ADR3) against the MAC address in the connection relationship information (Table 6) stored in the memory. If a match is found, the handover request function ( 14 - 2 ) of station STAL instructs the send/receive unit ( 12 ) to send packets to AP 3  thereafter.  
         [0159]     When notified of the reception of a packet from the send/receive unit, the handover processing function ( 4 - 3 ) of access point AP 3  searches the connection relationship information and upon finding an address matching the MAC address of the packet sender, it instructs the send/receive unit to send a movement notification packet to notify other access points in the group that the station has moved. At the same time, the handover processing function ( 4 - 3 ) of access point AP 3  instructs the send/receive unit to transfer the packet.  
         [0160]     After receiving a movement notification packet, the handover processing function ( 4 - 3 ) of the applicable access point updates the connection relationship information (station information). Tables 14, 15, 16 and 17 show the updated connection relationship information (station information).  
                                     TABLE 14                           Connection Relationship Information in AP1 before Movement       of STA1                Access point   Station   Station   Station           MAC address   MAC   MAC   MAC                       ADR1                       ADR2   STA1           ADR3                      
 
         [0161]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 15 
               
             
             
               
                   
               
               
                   
               
               
                 Connection Relationship Information in AP6 before Movement 
               
               
                 of STA1 
               
             
          
           
               
                   
                 Access point 
                 Station 
                 Station 
                 Station 
               
               
                   
                 MAC address 
                 MAC 
                 MAC 
                 MAC 
               
               
                   
                   
               
               
                   
                 ADR2 
                   
                   
                   
               
               
                   
                 ADR6 
                 STA1 
               
               
                   
                   
               
             
          
         
       
     
         [0162]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 16 
               
             
             
               
                   
               
               
                   
               
               
                 Connection Relationship Information in AP1 after Movement 
               
               
                 of STA1 
               
             
          
           
               
                   
                 Access point 
                 Station 
                 Station 
                 Station 
               
               
                   
                 MAC address 
                 MAC 
                 MAC 
                 MAC 
               
               
                   
                   
               
               
                   
                 ADR1 
                   
                   
                   
               
               
                   
                 ADR2 
                 (Deleted) 
               
               
                   
                 ADR3 
                 STA1 
               
               
                   
                   
                 (Added) 
               
               
                   
                   
               
             
          
         
       
     
         [0163]                                          TABLE 17                           Connection Relationship Information in AP6 after Movement of STA1                Access point   Station   Station   Station           MAC address   MAC   MAC   MAC                       ADR2   STA1                       (Added)           ADR6   (Deleted)                        
 (Packet Transfer Function) 
 
         [0164]     The access point transfers packets sent from other access point or station. A case where packets are sent from STA 1  under AP 6  to STA 2  under AP 3  in the network shown in  FIG. 31  is explained.  
         [0165]      FIG. 32  shows a packet transfer sequence between access points. When sending a packet to STA 2 , STA 1  under AP 6  sends the packet to access point AP 6  to which it is connected.  
         [0166]     The packet transfer function in access point AP 6  compares the address of the packet sending destination (STA 2 ) against the connection relationship information (station information) in the memory as shown in Table 11, and determines the access point to transfer the packet to (AP 2 ), and then instructs the send/receive unit ( 2 ) to transfer the packet to AP 2 . The send/receive unit ( 2 ) sends the packet to access point AP 2  via the wireless LAN port.  
                                     TABLE 11                           Station Information in AP6                Access point   Station   Station   Station           MAC address   MAC   MAC   MAC                       ADR2   STA2                   ADR6   STA1                      
 
         [0167]     Similarly, the packet transfer function in access point AP 2  compares the address of the packet sending destination (STA 2 ) against the connection relationship information (station information) in the memory as shown in Table 12, and determines the access point to transfer the packet to (AP 1 ), and then instructs the send/receive unit ( 2 ) to transfer the packet to AP 1 . The send/receive unit ( 2 ) sends the packet to access point AP 1  via the wireless LAN port. Similarly, access point AP 1  sends the packet to access point AP 3 .  
                                     TABLE 12                           Station Information in AP2                Access point   Station   Station   Station           MAC address   MAC   MAC   MAC                       ADR1   STA2                   ADR2           ADR6   STA1                      
 
         [0168]     The packet transfer function in access point AP 3  compares the address of the packet sending destination (STA 2 ) against the station information in the memory as shown in Table 13, and confirms that station STA 2  is under access point AP 3 , and then instructs the send/receive unit ( 2 ) to transfer the packet to STA 2 . The send/receive unit ( 2 ) sends the packet to STA 2  via the wireless LAN port.  
                                     TABLE 13                           Station Information in AP3                Access point   Station   Station   Station           MAC address   MAC   MAC   MAC                       ADR1                       ADR2   STA1           ADR3   STA2                      
 
         [0169]     The present invention can be applied for the purpose of extending the communication area of a wireless LAN and increasing the handover speed.