Abstract:
Any or unique VLAN ID is dynamically assigned to a user terminal connected to a network, and communication by the assigned VLAN ID is enabled. A connection request from a user terminal is directed to L2GWs by a tagged VLAN frame having a common VLAN ID on the network. The L2GWs determine whether the connection request can be met, obtain a VLAN ID that can be assigned to the user terminal from a VLAN ID management server, configure themselves to communicate by the assigned VLAN ID, and report the VLAN ID to the user terminal. The user terminal performs subsequent communication by the reported VLAN ID. L2SWs monitor communication between the user terminal and the L2GWs and configure themselves to allow communication between the user terminal and the L2GWs by the VLAN ID assigned to the user terminal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to user terminals, Layer 2 switches (L2SWs), and Layer 2 gateways (L2GWs) to which VLAN IDs can be dynamically assigned in network systems that can be connected to an Ethernet (registered trademark) network.  
         [0003]     2. Description of the Related Art  
         [0004]     In recent years, corporate LANs and other networks have a virtual group of certain terminals built as a virtual LAN (VLAN), independently of the physical structures of the networks. This technology allows a network to be built, irrespective of a change in terminal location or a change in network configuration caused by an organizational change. The network management cost can be reduced, and the network load can be reduced due to a broadcast packet limitation.  
         [0005]     One method of building a VLAN is to identify a VLAN by adding a VLAN tag to an Ethernet (registered trademark) frame header. This tag VLAN method allows a plurality of VLAN connections to be specified among apparatuses, giving flexibility to network configurations.  
         [0006]     When a user terminal is connected to an existing VLAN, the connection information must be specified to each apparatus on the VLAN, such as a hub. The generic attribute registration protocol (GARP) VLAN registration protocol (GVRP) (non-patent document  1 ) enables a dynamic connection of a terminal to a VLAN when the terminal is connected. This protocol broadcasts a connection request from the terminal to the VLAN, and the apparatuses in the VLAN configure the VLAN setting sequentially according to the information.  
         [0007]     A “Switching Hub with Default VLAN Configuration Function and VLAN Server” (patent document 1) has a function to connect a terminal which has not yet been registered to a system to a particular VLAN through a switching hub and to transfer the connection information to another switching hub.  
         [0008]     Non-patent document 1: IEEE std802. 1Q-1998 (chapter 11, pp.77-92)  
         [0009]     Patent document 1: Japanese Unexamined Patent Application Publication No. Hei-11-215152  
       SUMMARY OF THE INVENTION  
       [0010]     With the prior art, networks which provide a certain service, such as an access network, can accept a connection request to a VLAN network from particular user terminals or any number of unspecific user terminals after VLAN IDs are assigned to the user terminals, and work such as specifying MAC addresses and paths of the Layer 2 switches (L2SWs), routers, and other network apparatuses is also performed. Even when the GVRP can be used, advance VLAN ID assignment to user terminals is necessary, and an apparatus to which a user terminal is connected requires a configuration operation to enable communication by the VLAN ID assigned to the user terminal to be performed. The VLAN setting information is also required to be transferred to the other apparatuses. These configuration operations are carried out each time a maintenance cost. The VLAN ID assignment to user terminals requires the management of association between the user terminals and VLAN IDs, but the association information cannot be automatically specified in the individual user terminals. When a large number of user terminals are configured, a multiple specification of a VLAN ID and other errors can occur. The cost of the work including a configuration check will become enormous, and poor communication or a wrong connection, if any, will increase the network load.  
         [0011]     The known example described above is implemented just by switching hubs, and it is difficult to apply this example to a large system such as an inter-site VLAN.  
         [0012]     Accordingly, the present invention specifies a common VLAN ID of an entire network for connection from a user terminal to a VLAN and uses the common ID as a default VLAN ID in a VLAN ID assignment request. A user terminal configured to be able to execute connection processing on the default VLAN ID, a Layer 2 switch (L2SW) to serve the user terminal, and a Layer 2 gateway (L2GW) to serve the L2SW are provided. The L2GW or a management server provided on the network includes a management table for managing VLAN IDs that can be assigned. The L2GW includes a decision table indicating whether a service requested by the user terminal can be connected. The L2GW has a function to report an assigned VLAN ID to the user terminal and enables communication by the assigned VLAN ID. The L2SW can be configured to communicate by the VLAN ID to be reported, and the user terminal can be configured to communicate by the reported VLAN ID. request from a user terminal, on the default VLAN by a connection sequence of the Point-to-Point Protocol over Ethernet (PPPoE, registered trademark) protocol. The PPPoE connection sequence exchanges the following packets between the user terminal and the L2GW through the L2SW in a PPPoE discover session, or a series of protocol processing for establishing a connection session: PPPoE Active Discovery Initiation (PADI) packet, PPPoE Active Discovery Offer (PADO) packet, PPPoE Active Discovery Request (PADR) packet, and PPPoE Active Discovery Session-conformation (PADS) packet. The L2GW has a function to judge whether a connection can be made by the Service Name and can select the service requested by the user terminal or assign it to another L2GW. Of course, an authentication system outside the L2GW can judge whether a service can be connected. When a connection request to a user terminal can be accepted, the L2GW assigns a VLAN ID to the user terminal in accordance with the VLAN ID management table on the network or in the apparatus. A VLAN ID other than the default VLAN ID can be assigned by any rule: A unique ID is assigned or any ID is assigned within a certain range in accordance with the terminal MAC address, Service Name, user ID, and other information; or an unused ID is assigned at random. The L2GW is configured to communicate by the VLAN ID assigned to the physical port used by the connection request, and the assigned VLAN ID is reported to the user terminal as a session ID distributed to the user terminal by a PPPoE connection sequence. The L2SW monitors the PPPoE connection sequence, extracts a VLAN ID from the session ID when the reception of a PADS packet is found, enables communication by connection sequence, and transfers the PADS packet to the user terminal. The user terminal extracts a session ID from the received PADS packet and regards this ID as a VLAN ID. The subsequent communication is performed on the VLAN having the assigned VLAN ID. When an IP connection is made, for instance, an IP address and the like can be distributed through the use of DHCP, Radius, or another authentication system. A disconnection can be made by sending a PPPoE Active Discovery Terminate (PADT) packet from the user terminal or L2GW and canceling all the settings related to the assigned VLAN ID of the user terminal, L2SW, and L2GW.  
         [0013]     If the network allows the transfer of an untagged frame, when a PPPoE connection request is made by an untagged frame, without using the default VLAN, the L2GW determines whether the connection can be made in accordance with the terminal MAC address, Service Name, and other user information, and sends a VLAN ID, instead of the session ID, to the user terminal, and the user terminal performs communication by a tagged VLAN frame with the assigned VLAN ID, in the same way as for a normal PPPoE connection request.  
         [0014]     According to the present invention, a VLAN ID can be automatically assigned to each user terminal at random or uniquely just by specifying a common VLAN ID in the network to a user terminal that can be connected to the network, eliminating the need for specifying a VLAN ID to each user terminal. The VLAN configuration of each apparatus in the network is also automatically performed, and the network management including the VLAN ID management is facilitated. Because broadcast from the user terminal is allowed only on PPPoE connection request is made by an untagged frame, VLAN ID can be distributed by permitting untagged frame transfer on the network, and the subsequent communication is performed on the VLAN, making it possible to reduce the network load. The VLAN ID can be embedded in the session ID of the PPPoE protocol, and the distinction of service and the selection of L2GW can be made in accordance with the Service Name tag. These functions can be implemented without changing the PPPoE protocol. The user terminal, L2SW, and L2GW do not require any modification, except for modifications to software including the addition of a management table. Accordingly, the present invention can be implemented at a low cost. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows a network configuration according to a first embodiment of the present invention.  
         [0016]      FIGS. 2-1  to  2 - 3  are block diagrams showing the configurations of a terminal  101 , an L2SW  102 , and an L2GW  103  according to the first embodiment.  
         [0017]      FIGS. 3-1  and  3 - 2  are views showing the configuration of a VLAN frame  106  according to the first embodiment.  
         [0018]      FIGS. 4-1  and  4 - 2  are system sequence diagrams according to the first embodiment.  
         [0019]      FIGS. 5-1  to  5 - 5  are flow charts showing the operation of the terminal  101  according to the first embodiment.  
         [0020]      FIGS. 6-1  to  6 - 6  are flow charts showing the operation of the L2SW  102  according to the first embodiment.  
         [0021]      FIGS. 7-1  to  7 - 4  are flow charts showing the operation of  FIGS. 8-1  to  8 - 10  show management tables according to the first embodiment.  
         [0022]      FIGS. 9-1  to  9 - 26  show state changes in the management tables according to the first embodiment.  
         [0023]      FIG. 10  shows a network configuration according to a second embodiment of the present invention.  
         [0024]      FIG. 11  is a block diagram showing the configuration of an L2GW  103  according to the second embodiment.  
         [0025]      FIG. 12  shows a management table according to the second embodiment.  
         [0026]      FIGS. 13-1  and  13 - 2  are system sequence diagrams according to the second embodiment.  
         [0027]      FIGS. 14-1  to  14 - 3  are flow charts showing the operation of the L2GW  103  according to the second embodiment.  
         [0028]      FIGS. 15-1  to  15 - 3  show state changes in the management table according to the second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     A. First Embodiment  
       [0029]     A first embodiment of the present invention will be described below with reference to the drawings. In the following description of the first embodiment, a default VLAN ID is specified. The same processing is performed for an untagged VLAN frame containing a PPPoE connection request, which will be described later.  
         [0000]      1 . System Configuration  
         [0030]      FIG. 1  shows a network configuration of the first embodiment. The network shown in  FIG. 1  includes user terminal units  100 - 1  to  100 - n  and  101 - 1  to  101 -n, L2SWs  102 - 1  to  102 - x  which serve the terminal units, L2GWs  103 - 1  to  103 - y  which serve the L2SWs, a host network  104  connected to the L2GWs, and a VLAN ID management server  105  connected to the network. Communication from the terminal units  100 - 1  to  100 - n  and  101 - 1  to  101 - n  to the host network  104  is performed by a tagged VLAN frame  106 . An IP packet and other data are transferred in the tagged VLAN frame.  
         [0031]      FIG. 2-1  shows the configuration of the terminal units  100 - 1  to  100 - n  and  101 - 1  to  101 - n . The terminal units  101 - 1  to  100 - n  and  101 - 1  to  101 - n  include a processor  202  for controlling a terminal and performing a variety of processing, a memory  224  for storing processing and statuses of the terminal, a protocol processing processor  221  for managing protocol processing and other processing, a buffer  222  for buffering a frame processed by the protocol processing processor  221 , and a channel interface  223  for performing transmission and reception of frame information. The processor  220  handles a communication request from a user in accordance with connection-disconnection processing  2241 , timer processing  2242 , and a connection management table  2243  on the memory  224 , gives an instruction to the protocol processing processor  221 , and monitors the status of the protocol processing processor  221 . The protocol processing processor  221  monitors the status of the buffer  222 , handles a frame received by the channel interface  223 , and reports the status to the processor  220 . The processor  220  or the protocol processing processor  221  performs processing as illustrated in flow charts and sequence diagrams below.  
         [0032]      FIG. 2-2  shows the configuration of the L2SWs  102 - 1  to  102 - x . The L2SWs  102 - 1  to  102 - x  include a plurality of input-output channel interfaces  2001  to  2003 ,  2041 , and  2042 , buffers  2011  to  2013 ,  2031 , and  2032  for buffering frame information sent and received by the channel interfaces  2001  to  2003 ,  2041 , and  2042 , a switch (SW)  202  for exchanging or transferring frames between the channel interfaces  2001  to  2003 ,  2041 , and  2042 , a processor  205  for controlling the components mentioned above, and a memory  206  for holding the status of the L2SW. The processor  205  monitors the statuses of the channel interfaces  2001  to  2003 ,  2041 , and  2042  and the buffers  2011  to  2013 ,  2031 , and  2032 , and sets the status of the SW  202  for the frame arriving at the channel interfaces  2001  to  2003 ,  2041 , and  2042 , in accordance with connection-disconnection processing  2061 , port processing  2062 , timer processing  2063 , a connection management table  2064 , and a port management table  2065  on the memory  206 . The processor  205  performs processing as illustrated in flow charts and sequence diagrams below.  
         [0033]      FIG. 2-3  shows the configuration of the L2GWs  103 - 1  to  103 - y . The L2GWs  103 - 1  to  103 - y  include a plurality of input-output channel interfaces  2101  and  2102 , a channel interface  2103  connected to the host network  104 , a protocol processing block  211 , and a control block  212  for controlling the protocol processing block  211 . The control block  212  monitors the status of the protocol processing block  211 , reports the status to a control terminal  213 , specifies control parameters of the protocol processing block  211  in accordance with an instruction from the control terminal  213 , and transfers a frame received from the protocol processing block  211  to channel interfaces  2101  to  2103  having an output port.  
         [0034]     The protocol processing block  211  includes buffers  2111  to  2113  for buffering frames processed by the channel interfaces  2101  to  2103 , a protocol processing processor  2121  for executing protocol processing, and a processor-to-processor interface  2123  for communicating with the control block  212 . The protocol processing block  211  controls the L2GW  103 - 1  or  103 - y  as instructed by the control block  212 , in accordance with connection-disconnection processing  21221 , Service Name decision processing  21222 , port processing  21223 , timer processing  21224 , a terminal management table  21225 , a port management table  21226 , and a Service Name decision table  21227  on the memory  2122 . The protocol processing block  211  performs processing as illustrated in flow charts and sequence diagrams below.  
         [0035]      FIG. 3-1  shows a VLAN frame format used in the present embodiment. The VLAN frame includes an Ethernet (registered trademark) header  308  and a payload  309 . The Ethernet (registered trademark) header  308  includes a transmission destination MAC address  301 , a transmission source MAC address  302 , a first protocol type VLAN  303 , a priority level  304 , a VLAN ID  305 , and a second protocol type PPPoE  306  (PADI, PADO, or the like). The priority level  304 , the VLAN ID  305 , and the second protocol type PPPoE  306  are referred to as VLAN tag information  310 .  
         [0036]      FIG. 3-2  shows the format of a PPPoE packet  307  contained in the payload  309  of the VLAN frame shown in  FIG. 3-1 . The PPPoE packet  307  includes a version (Ver)  311 , a type  312 , a code  313 , a session ID  314 , a length  315 , a tag type  316 , a specified, for instance, the tag type  316  is set to “0X0101”, and the Service Name is specified in the tag value field  318 .  
         [0037]      FIG. 8-1  shows the connection management table  2243  of the terminal units  100 - 1  to  100 - n  and  101 - 1  to  101 - n . The management table includes a VLAN ID 801801 being connected, the MAC address 801802 of the L2GW  103 - 1  to  103 - y  being connected, a Service Name 801803 being connected, a connection status 801804, and a timer status 801805. Sample settings are shown in the table.  
         [0038]      FIG. 8-2  shows the connection management table  2064  of the L2SWs  102 - 1  and  102 - x . The connection management table includes a VLAN ID 801806, a terminal-side physical port number 801807, a terminal MAC address 801808, an L2GW-side physical port number 801809, an L2GW MAC address (801810), a connection status 801811, and a timer status 801812.  FIG. 8-3  shows the port management table  2065  of the L2SWs. The port management table includes a physical port number 801813 and a VLAN ID 801814. The figure shows sample settings.  
         [0039]      FIG. 8-7  shows the connection management table  21225  of the L2GWs  103 - 1  and  103 - y . The connection management table includes a VLAN ID 801815, a terminal MAC address 801816, an L2GW physical port number 801817, a connection status 801818, and a timer status 801819.  FIG. 8-8  shows the port management table 21226 of the L2GWs. The management table includes a physical port number 801820 and a VLAN ID 801821.  FIG. 8-9  shows the Service Name decision table 21227 of the L2GW. The decision table includes a Service Name 801822. The figures show sample settings.  
         [0040]      FIG. 8-10  shows the VLAN ID management table provided in includes a VLAN ID 801825, a usage state 801826, and a registered L2GW 801827. The figure shows sample settings.  
         [0000]      2 . Connection Sequence  
         [0041]      FIG. 4-1  is a connection sequence diagram according to the present invention. The sequence will be described with reference to the sequence diagram.  
         [0000]     (1) Initialization  
         [0042]     When the system starts up, the apparatuses are initialized.  
         [0043]     In the terminals  100 - 1  to  100 - n  and  101 - 1  to  101 - n , the connection management table is initialized, as shown in  FIG. 9-1 . The VLAN ID 901911 is set to the default VLAN ID shared in the system, which is VLAN 1 , in this embodiment. The L2GW MAC address 9019021 is set to a broadcast address. Nothing is specified as the Service Name 9019031. The connection status 9019041 is set to “DISCONNECTED”, and the timer status 9019051 is set to “STOP”.  
         [0044]     In the L2SWs  102 - 1  to  102 - x , the connection management table and the port management table are initialized as shown in  FIGS. 9-7  and  9 - 14 . In the connection management table, the VLAN ID 9019061 is set to the default VLAN ID “VLAN1”; the terminal-side physical port number 9019071, the terminal MAC address 9019081, the L2GW-side physical port number 9019091, and the L2GW MAC address 9019101 are left unregistered; the connection status 9019111 is set to “DISCONNECTED”; and the timer status 90199112 is set to “STOP”. In the port management table, the default VLAN ID “VLAN1” is specified for each physical port is specified in accordance with the port management table, so that a VLAN frame can be exchanged. An item broadcast to VLAN 1  is output to all the ports, but the L2SW is configured to inhibit broadcast from the terminal  101 - 1  to anything other than the L2GWs  103 - 1  to  103 - y , as shown in  FIG. 8-4 . For instance, just broadcast to an upper port can be allowed while broadcast to lower physical ports on the side of the terminal units is inhibited. This configuration suppresses unnecessary broadcast to a user terminal or something other than a specified port and reduces traffic.  
         [0045]     In the L2GWs  103 - 1  to  103 - 7 , the connection management table, port management table, and Service Name decision table are initialized as shown in  FIGS. 9-17 ,  9 - 21 , and  8 - 9  respectively. In the connection management table, the VLAN ID 9019151 is set to the default VLAN ID “VLAN1”; the terminal MAC address 9019161 and the L2GW physical port number 9019171 are left unregistered; the connection status 9019181 is set to “DISCONNECTED”; and the timer status 9019191 is set to “STOP”. In the port management table, “VLAN1” 9019211 to 9019212 is specified for all the physical ports 9019201 and 9019202. In the Service Name decision table, serviceable service names 8018221 to 8018223 are registered.  
         [0046]     In the VLAN ID management server  105 , the VLAN ID management table is initialized as shown in  FIG. 9-24 . In the VLAN ID management table, a default VLAN ID flag is specified as the usage state 9019251 and “RESERVE” is specified as the registered L2GW 9019261, for the VLAN ID 9019241. For the other LAN IDs 9019242 and 9019243, the usage states 9019252 and 9019253 and the registered L2GWs 9019262 and 9019263 are  
         [0000]     (2) Terminal: PADI Transmission  
         [0047]     The terminal  101 - 1  starts a PADI transmission sequence S 101 . A flow chart of the processing is shown in  FIG. 5-1 . In this sequence, a PADI packet is generated in accordance with the connection management table shown in  FIG. 9-1 , and the PADI packet is encapsulated in a tagged VLAN frame having the VLAN ID “VLAN1” and broadcast. The PADI packet contains a VLAN ID, an L2GW MAC address, a Service Name, and others. In the connection management table, the connection status 9019041 is set to “PADO WAIT”, and the timer status 9019051 is set to “COUNTING”, as shown in  FIG. 9-2 . Then, the timer is activated, and a response from the L2GW is waited for.  
         [0000]     (3) L2SW: PADI Monitoring  
         [0048]     The broadcast frame reaches the L2SW  102 - 1 , and the PADI monitoring sequences S 102 - 1  and S 102 - y  start. A flow chart of the processing is shown in  FIG. 6-1 . If the received frame is a tagged VLAN frame which has the default VLAN ID “VLAN1” and contains a PADI packet, the VLAN frame is transferred to the L2GWs  103 - 1  to  103 - y . At the time of transfer, the number of the physical port where the frame is received “P01” and the transmission source MAC address “0×000000001001” are specified as the terminal-side physical port number 9019071 and the terminal MAC address 9019081, in the connection management table, as shown in  FIG. 9-8 . The connection status is set to “PADO WAIT”, and the timer status is set to “COUNTING”. Then, the timer is activated, and the L2SW starts monitoring a PADO from the L2GWs. A VLAN ID frame which is being connected but doesnot meet the conditions given above is handled as a normal VLAN frame in step  610 . A default VLAN ID frame containing a PADR packet is handled in PADR monitoring in step  639 . The other frames are discarded in step  611 , and the PADI monitoring sequence ends. In the VLAN frame transfer to the L2GW, the port management table as shown in  FIG. 8-3  is referenced, and the frame can be transferred only to a physical port having the default VLAN ID, as shown in  FIG. 8-4 . For instance, the frame can be transferred to an upstream L2GW and not to a downstream physical port on the side of the terminal units.  
         [0000]     (4) L2GW: PADI Reception  
         [0049]     The broadcast frame reaches the L2GWs  103 - 1  to  103 - y , which individually start the PADI reception sequences S 103 - 1  and S 103 - y . A flow chart of the processing is shown in  FIG. 7-1 . If the received frame is a tagged VLAN frame which has the default VLAN ID “VLAN1” and contains a PADI packet, a Service Name match decision  706  is made in this sequence. “NONE” in  FIG. 8-9  means that at least a connection is identified.  
         [0050]     If the Service Name extracted from the PADI packet does not match any data stored in the service decision table shown in  FIG. 8-9 , the frame is discarded in step  712 , and the PADI reception sequence ends. If the Service Name matches any data, the number of the physical port where the frame is received “P21” and the transmission source MAC address “0×000000001001” are specified as the L2GW physical port number 9019171 and the terminal MAC address 9019161 in the connection management table, as shown in  FIG. 9-18 . In addition, the connection status is set to “PADR WAIT” and the timer status is set to “COUNTING”, and the PADO packet transmission of step  708  is performed. The timer is activated, and the L2GW waits for a PADR response from the terminal. An example for the L2GW  103 - y  has been described here, and the same processing is performed for the L2GW  103 - 1 . A VLAN frame which does not meet the conditions given above and has a VLAN ID being connected is handled as a normal VLAN frame in step  711 . The other frames are discarded in step  712 , and the PADI reception sequence ends.  
         [0000]     (5) L2SW: PADO Monitoring  
         [0051]     When default VLAN frames containing PADO from the L2GWs  103 - 1  and  103 - y  reach the L2SW  102 - 1 , the PADO monitoring sequences S 104 - 1  and S 104 - y  start. A flow chart of the processing is shown in  FIG. 6-2 . If the received frame is a tagged VLAN frame which has the default VLAN ID and contains a PADO packet and if the transmission destination MAC address extracted in step  619  is contained in the terminal MAC address 9019081 and the connection status is “PADO WAIT” 9019111 in the connection management table, as shown in  FIG. 9-8 , the number of the physical port where the frame is received “Ply” and the transmission source MAC address “0×000000001032”, and “PADR wait” are specified respectively as the L2GW-side physical port number 9019091, the L2GW MAC address 9019101, and the connection status 9019111, as shown in  FIG. 9-9 , and the frame transfer to the terminal is performed in step  629 . When a default VLAN frame containing PADO is received from the L2GW  103 - 1 , if the extracted transmission destination MAC address is included in the connection management table, and if the connection status is “PADR WAIT”, in step  631 , the connection information 9019062 to 9019122 of the L2GW  103 - 1  is added to the connection management table, as shown in  FIG. 9-10 . The VLAN ID, terminal-side physical port number, terminal MAC address, connection information, and timer status are taken from the connection information which includes the extracted transmission destination MAC address and the connection status “PADR WAIT”. The L2GW-side physical port number and the L2GW MAC address are set to the physical port number and the MAC address to which the L2GW  103 - 1  is connected. Then, the frame transfer to the terminal is performed. Each time a default VLAN frame containing PADO is received and it is checked that the extracted transmission destination MAC address is included in the connection management table and that the connection status is “PADR WAIT”, the sequence described above is repeated. A VLAN ID frame which does not meet the conditions described above and is being connected is handled as a normal VLAN frame in step  622 . A default VLAN ID frame containing a PADS packet is handled in a PADS monitoring sequence of step  653 . The other frames are discarded in step  633 , and the PADI monitoring sequence ends.  
         [0000]     (6) Terminal: PADO Reception  
         [0052]     The frame reaches the terminal  101 - 1 , and a PADO reception sequence S 105  starts. A flow chart of the processing is shown in  FIG. 5-2 . This sequence checks if the received frame is a tagged VLAN frame, if the frame has the default VLAN ID, if the frame contains a PADO packet, if the connection status in the connection management table is “PADO WAIT” 9019041, as shown in  FIG. 9-2 , and if the Service Name extracted from the PADO packet in step  512  is registered. Then, the L2GW MAC address 9019021 is set to the transmission source MAC address “0×000000001032” in step  514 , as shown in  FIG. 9-3 ; the “PADS wait” flag 9019041 is set in step  515 , as shown in  FIG. 9-4 ; a PADR packet corresponding to the transmission source address is generated in step  516 ; and the packet is contained in a tagged VLAN frame having the default VLAN ID and sent to the L2GW  103 - y . If the frame has a VLAN ID being connected, the frame is received in step  520 . The other frames are discarded in step  521 . If the Service Name does not match, the next frame will be processed. When the terminal enters the PADS wait state next or when a timeout of the PADO wait timer occurs next, the PADO reception sequence ends. The L2GW  103 - 1  also sends a PADO packet, but the corresponding frame will be discarded when the terminal enters the PADS wait state.  
         [0000]     (7) L2SW: PADR Monitoring  
         [0053]     The frame reaches the L2SW  102 - 1 , and a PADR monitoring sequence S 106 - y  starts. A flow chart of the processing is shown in  FIG. 6-3 . This sequence checks if the received frame is a tagged VLAN frame having a default VLAN ID, if the frame contains a PADR packet, and if the transmission source MAC address and the transmission destination MAC address extracted from the PADR packet in step  639  match the terminal MAC address 901907 and the L2GW MAC address 901910 respectively in the connection management table as shown in  FIG. 9-11 . Then, the corresponding connection status 9019111 is set to “PADS WAIT” in step  643 ; the PADR wait timer is stopped; a PADS wait timer is activated to bring the connection into the PADS wait state; and the rifle is transferred to the L2GW  103 - y  in step  645 . If the transmission source MAC address extracted from the PADR packet matches the terminal MAC address 9019072 in the connection management table, as shown in  FIG. 9-11 , and if the transmission destination MAC address extracted from the PADR packet does not match the L2GW MAC address 9019102 in the connection management table, as shown in  FIG. 9-11 , the connection information is deleted in step  644 . A VLAN ID frame which does not meet the conditions given above and is being connected is handled as a normal VLAN frame in step  648 . A default VLAN ID frame containing a PADI packet is handled in a PADI monitoring sequence of step  605 . The other frames are discarded in step  651 , and the PADR monitoring sequence ends.  
         [0000]     (8) L2GW: PADR Reception  
         [0054]     The frame reaches the L2GW  103 - y , and a PADR reception sequence S 107 - y  starts. A flow chart of the processing is shown in  FIG. 7-2 . This sequence checks if the received frame is a tagged VLAN frame having a default VLAN ID, if the frame contains a PADR packet, and if the transmission source MAC address extracted from the PADR packet matches the terminal MAC address 901916 in the connection management table, as shown in  FIG. 9-19 . Then, a request for a VLAN ID is made to the VLAN ID management server  105  in sequence S 1061 - y.    
         [0000]     (9) VLAN ID Management Server: ID Assignment  
         [0055]     The VLAN ID management server  105  chooses any ID 9019242 from unused IDs in the VLAN ID management table, as shown in  FIG. 9-24 ; sets an “OCCUPIED” flag as the usage state 9019252 in the VLAN ID management table, as shown in  FIG. 9-25 ; sets the assigned L2GW  103 - y  as the registered L2GW 9019262, as shown in  FIG. 9-25 ; and reports the assigned VLAN ID to the L2GW  103 - y  in sequence S 1062 - y . In this embodiment, the assigned VLAN ID is VLAN 2 .  
         [0000]     (10) L2GW: Registration  
         [0056]     The L2GW  103 - y  opens a VLAN port for the physical port of the L2GW physical port number “P21” in the connection management table as shown in  FIG. 9-19 , and adds the VLAN ID “VLAN2” as the corresponding physical port number in the L2GW port management table, as shown in  FIG. 9-22 . The VLAN ID 9019151 is set to the assigned VLAN ID “VLAN2”, and the connection status 9019181 is set to “CONNECTING”, in the connection management table, as shown in  FIG. 9-19 . A PADS packet having the VLAN ID “VLAN2” as a session ID is generated, encapsulated in a default VLAN frame, and transferred to the terminal  101 - 1 . If the VLAN port cannot be successfully opened, the corresponding connection information is deleted from the connection management table in step  728 . If a timeout of the PADR wait timer occurs, the corresponding connection information is deleted. A VLAN ID frame which does not meet the conditions given above and is being connected is processed as a normal VLAN frame in step  730 . The other frames are discarded in step  727 , and the PADR reception sequence ends.  
         [0000]     (11) L2SW: PADS Monitoring  
         [0057]     The frame reaches the L2SW  102 - 1 , and a PADS monitoring sequence S 108 - y  starts. A flow chart of the processing is shown in  FIG. 6-4 . This sequence checks if the received frame is a tagged VLAN frame having a default VLAN ID, if the frame contains a PADS packet, if the transmission source MAC address and transmission destination MAC address extracted from the PADS packet match the L2GW MAC address 901910 and the terminal MAC address 901908 in the connection management table, as shown in  FIG. 9-11 , and if the corresponding connection is in the PADS wait state. Then, the session ID “VLAN2” is extracted from the PADS packet; the VLAN ports of the assigned VLAN ID are opened for the physical ports of the terminal-side physical port number 901907 and the L2GW-side physical port number 901909 of the connection management table, as shown in  FIG. 9-12 , in step  659 . The VLAN ID 9019061 is set to the assigned VLAN ID “VLAN2”; the connection status 9019111 is set to “CONNECTING”; and the timer status 9019121 is set to “HALT”, in step  661 . The assigned VLAN ID “VLAN2” is set to the physical ports 9019141 and 9019145 for which the VLAN ports of the port management table shown in  FIG. 9-15  have been opened. The received frame is transferred to the terminal side in step  662 . If any of the VLAN ports cannot be successfully opened, the corresponding connection information is deleted from the connection management table. A VLAN ID frame which does not meet the conditions given above and is being connected is handled as a normal VLAN frame in step  665 . A tagged VLAN frame which has the default VLAN ID and contains a PADO packet is handled in a PADO monitoring sequence of step  619 . The other frames are discarded in step  668 . If a timeout of the PADS wait timer occurs, the corresponding connection information is deleted. Then, the PADR reception sequence ends.  
         [0000]     (12) Terminal: PADS Reception  
         [0058]     The frame reaches the terminal  101 - 1 , and a PADS reception sequence of S 109  starts. A flow chart of the processing is shown in  FIG. 5-3 . This sequence checks if the received frame is a tagged VLAN frame having the default VLAN ID, if the frame contains a PADS packet, and if the extracted transmission source MAC address matches an L2GW MAC address in the connection management table, as shown in  FIG. 9-4 . Then, the VLAN ID “VLAN2” assigned from the session ID extracted from the PADS packet is specified as the VLAN ID 9019011 of the corresponding connection information in the connection management table, as shown in  FIG. 9-5 ; the connection status 9019041 is set to “CONNECTING”; the timer status 9019051 is set to “STOP”; and the sequence ends. If a timeout of the PADS wait timer occurs, the corresponding connection information is deleted from the connection management table.  
         [0000]     ( 13 ) Communication  
         [0059]     Now, the terminal  101 - 1  and the -L2GW  103 - y  communicate through the L2SW  102 - 1 , using the assigned VLAN ID on the VLAN network. Any protocol using the Ethernet (registered trademark) frame can be used for the communication. If IP is used, an IP address is obtained by DHCP, and an authentication system such as Radius can be combined to provide a variety of services. The user terminal belongs to a unique VLAN network, and broadcast to a port outside VLAN 2  is suppressed, as shown in  FIGS. 8-5  and  8 - 6 , so that the network load can be reduced. With Service Name, the connection destination and connection route of each service can be limited, and the network can be effectively used.  
         [0000]     3. Disconnection Sequence  
         [0060]     Disconnection processing will be described. A PADT packet of the PPPoE protocol is used in the disconnection processing. The processing can be started from either the terminal or the L2GW.  
         [0000]     3-1. Disconnection from the L2GW  
         [0000]     (1) L2GW: PADT Transmission  
         [0061]     If a disconnection is made from the L2GW, the L2GW  103 - y  starts a PADT transmission sequence S 109 - y . A flow chart of the processing is shown in  FIG. 7-3 . The VLAN ID and terminal MAC address of the terminal  101 - 1  to be disconnected are selected from the connection management table, as shown in  FIG. 9-19 ; a PADT packet is generated with the session ID set to the VLAN ID to be disconnected “VLAN2”, the transmission destination MAC address set to the terminal MAC address, and the transmission source MAC address set to the MAC address corresponding to the L2GW physical port number associated with the terminal; and the packet is encapsulated in a tagged VLAN frame having the VLAN ID “VLAN2” to be disconnected and sent to the terminal  101 - 1 . After the frame is sent, the VLAN port to which “VLAN2” is assigned is closed, and the VLAN ID management server is requested to delete the VLAN ID, in a sequence S 1091 - y . The L2GW  103 - y  also initializes the connection information corresponding to the VLAN ID to be disconnected in the connection management table, as shown in  FIG. 9-20 , and the VLAN ID is deleted from the physical port management table, as shown in  FIG. 9-23 .  
         [0062]     The VLAN ID management server deletes the specified VLAN ID from the VLAN ID management table, as shown in  FIG. 9-26 .  
         [0000]     (3) L2SW: PADT Monitoring  
         [0063]     The L2SW  102 - 1  receives the frame and starts a PADT monitoring sequence of S 110 - y . A flow chart of the processing is shown in  FIG. 6-5 . This sequence checks if the received frame is a tagged VLAN frame having a VLAN ID being connected and if the frame contains a PADT packet. Then, the received frame is transferred to the terminal  101 - 1 . In the connection management table, the VLAN ID 9019061 is set to the default VLAN ID; the terminal-side physical port number 9019071, the terminal MAC address 9019081, the L2GW-side physical port number 9019091, and the L2GW MAC address 9019101 are set to “NOT REGISTERED”, and the connection status 9019111 is set to “NOT CONNECTED”, as shown in  FIG. 9-13 . Another frame having a VLAN ID being connected is received in step  692 . A frame having the default VLAN ID is subjected to connection processing in step  691 . The other frames are discarded in step  693 .  
         [0000]     (4) Terminal: PADT Reception  
         [0064]     The terminal  101 - 1  receives the frame and starts a PADT reception sequence. A flow chart of the processing is shown in  FIG. 5-4 . This sequence checks if the received frame is a tagged VLAN frame having VLAN ID “VLAN2” being connected and if the frame contains a PADT packet. Then, the VLAN port is closed, and the connection information is deleted from the connection management table, as shown in  FIG. 9-6 . In this If the received frame is a tagged VLAN frame which has a VLAN ID being connected and something other than a PADT packet, the frame is received in step  542 . If the frame has the default VLAN ID, the frame is subjected to connection processing in step  541 . The other frames are discarded in step  543 .  
         [0000]     3-2. Disconnection from the Terminal  
         [0000]     (1) Terminal: PADT Transmission  
         [0065]     If a disconnection is made from the terminal, the terminal  101 - 1  starts a PADT transmission sequence S 111 . A flow chart of the processing is shown in  FIG. 5-5 . This sequence determines the VLAN-ID or L2GW to be disconnected; obtains the VLAN ID 901901 and the L2GW MAC address 901902 from the connection management table as shown in  FIG. 9-5 ; generates a PADT packet with the session ID set to the VLAN ID “VLAN2” to be disconnected, the transmission destination MAC address set to the L2GW MAC address, the transmission source MAC address set to the terminal MAC address; encapsulates the packet in a tagged VLAN frame having the VLAN ID “VLAN2” and sends it to the L2GW  103 - y . After the frame is sent, the VLAN port to which “VLAN2” is assigned is closed, and the connection information corresponding to the VLAN ID to be disconnected is deleted from the connection management table, as shown in  FIG. 9-6 .  
         [0000]     (2) L2SW: PADT Monitoring  
         [0066]     The L2SW  102 - 1  receives the frame and starts a PADT monitoring sequence S 112 - y . A flow chart of the processing is shown in  FIG. 6-6 . This sequence checks if the received frame is a tagged VLAN frame having the VLAN ID “VLAN2” being connected and if the frame contains a PADT packet. Then, the received frame is transferred to the L2GW  103 - y . In the connection management table shown in  FIG. 9-13 , the VLAN ID 9019061 is set to the default VLAN ID; the terminal-side physical port number 9019071, the terminal MAC address 9019081, the L2GW-side physical port number 9019091, and the L2GW MAC address 9019101 are set to “NOT REGISTERED”, and the connection status 9019111 is set to “NOT CONNECTED”. Another frame having a VLAN ID being connected is received in step  680 . A frame having the default VLAN ID is subjected to connection processing in step  679 . The other frames are discarded in step  681 .  
         [0000]     (3) L2GW: PADT Reception  
         [0067]     The L2GW  103 - y  receives the frame and starts a PADT reception sequence. A flow chart of the processing is shown in  FIG. 7-4 . This sequence checks if the received frame is a tagged VLAN frame having a VLAN ID being connected and if the frame contains a PADT packet. Then, the VLAN ID is extracted from the received frame; the VLAN port of the physical port to which the VLAN ID is assigned in the connection management table is closed; and a request to delete the VLAN ID is made to the VLAN ID management server in sequence S 1121 - y . The L2GW  103 - y  also initializes the connection information corresponding to the VLAN ID to be disconnected in the connection management table, as shown in  FIG. 9-20 , and the VLAN ID to be disconnected is deleted from the physical port management table, as shown in  FIG. 9-23 .  
         [0000]     (4) VLAN ID Management Server: ID Deletion  
         [0068]     The VLAN ID management server deletes the specified VLAN ID from the VLAN ID management table.  
       B. Second Embodiment  
       [0069]     The VLAN ID management table of the first embodiment is on the VLAN ID management server while the VLAN ID management table of a second embodiment is in L2GWs.  
         [0070]      FIG. 10  shows a network configuration of the second embodiment. As shown in the figure, the network includes user terminal units  100 - 1  to  100 - n  and  101 - 1  to  101 - n , L2SWs  102 - 1  and  102 - x  for serving the terminal units, L2GWs  1003 - 1  and  1003 - y  for serving the L2SWs, a host network  104  connected to the L2GWs, and a control network  1005  for connecting the L2GWs. A tagged VLAN frame  106  is used for communication from the terminal units  100 - 1  to  100 - n  and  101 - 1  to  101 - n  to the host network  104 , and an IP packet and other data are transferred in the tagged VLAN frame. The L2GWs  1003 - 1  to  1003 - y  contain one VLAN ID management table each, and the VLAN ID management tables can be synchronized through the control network  1005  at any timing. The tables may also be synchronized through the host network.  
         [0071]      FIG. 11  shows the configuration of the L2GWs  1003 - 1  and  1003 - y  of the second embodiment. The L2GWs  1003 - 1  and  1003 - y  include a plurality of input-output channel interfaces  2101  and  2102 , a channel interface  2103  connected to the host network, a protocol processing block  211 , and a control block  212  for controlling the protocol processing block  211 . The control block  212  monitors the status of the protocol processing block  211 , reports the status to a control terminal  213 , sets control parameters of the protocol processing block  211  in response to an instruction from the control terminal  213 , and transfers a frame received from the protocol processing block  211  to the channel interfaces  2101  to  2103  containing output ports.  
         [0072]     The protocol processing block  211  contains buffers  2111  to  2113  for buffering frames to be processed by the channel interfaces  2101  to  2103 , a protocol processing processor  2121  for executing protocol processing, and a processor-to-processor interface  2123  for communicating with the control block  212 . The protocol processing block  211  controls the L2GW  103 - 1  or  103 - y  in accordance with connection-disconnection processing  21221 , Service Name decision processing  21222 , port processing  21223 , timer processing  21224 , a terminal management table  21225 , a port management table  21226 , a Service Name decision table  21227 , and a VLAN ID management table  1012201 , as instructed by the control block  212 . The control terminal  213  is connected to the control network  1005  and controls communication between the L2GWs  1003 - 1  and  1003 - y.    
         [0073]      FIG. 12  shows the VLAN ID management table  1012201  of the L2GWs  1003 - 1  to  1003 - y . The management table includes a usable VLAN ID 1201823 and a usage state thereof 1201824. The figure shows sample settings.  
         [0074]     The other part of the configuration is the same as in the first embodiment.  
         [0075]      FIGS. 13-1  and  13 - 2  show a connection sequence and a disconnection sequence of the second embodiment. Only differences from the first embodiment will be described with reference to the sequence diagrams  
         [0076]     When the apparatuses are initialized at system startup, the VLAN ID management tables of the L2GWs  1003 - 1  and  1003 - y  are initialized as shown in  FIG. 15-1 .  
         [0077]     In the connection sequence, frame reception sequences S 101 , S 102 - 1 , and S 102 - y  from the terminal unit  101 - 1  to the L2GWs  1003 - 1  and  1003 - y , frame reception sequences S 103 - y , S 103 - 1 , S 104 - y , and S 104 - 1  from the L2GWs  1003 - 1  and  1003 - y  to the terminal  101 - 1 , and frame reception sequences S 106  and S 106 - y  from the terminal  101 - 1  to the L2GWs  1003 - 1  and  1003 - y  are the same as in the first embodiment.  
         [0078]     The L2GW  103 - y  receives a frame containing PADR and starts a PADR reception sequence  107 - y . A flow chart of the processing is shown in  FIG. 14-1 . This sequence differs from that in the first embodiment in that the L2GW determines the VLAN ID to be assigned to the terminal in step  14720 . The VLAN ID to be used is determined, and an “OCCUPIED” flag  15019232  is set in the VLAN ID management table, as shown in  FIG. 15-2 . The VLAN ID can be determined by any rule. The L2GW  1003 - y  reports the occupied VLAN ID to another L2GW  1003 - 1 . The L2GW  1003 - 1  specifies in the internal VLAN ID management table that the reported VLAN ID is occupied  15019232 , as shown in  FIG. 15-2 . The other part of the processing is the same as in the first embodiment. A PADS packet is sent to the terminal unit  101 - 1 .  
         [0079]     The disconnection sequence will be described next. When the L2GW  1003 - y  starts a disconnection sequence, a PADT transmission sequence S 109 - y  starts. A flow chart of the processing is shown in  FIG. 14-2 . This sequence differs from that of the first embodiment in that the VLAN ID to be disconnected is deleted from the internal connection management table. The L2GW  1003 - y  specifies a “NOT USED” flag  15019232  for the VLAN ID to be disconnected in the connection management table, as shown in  FIG. 15-3 . The VLAN ID to be disconnected is reported to another L2GW  1003 - 1 . The L2GW  1003 - 1  specifies that the reported VLAN ID is not used  15019232 , in the internal VLAN ID management table, as shown in  FIG. 15-3 . The other part of the processing is the same as in the first embodiment, and a PADT packet is sent to the terminal unit  101 - 1 . When the terminal unit  101 - 1  starts disconnection, the L2GW  1003 - y  receives a frame containing PADT and starts a PADT reception sequence. A flow chart of the processing is shown in  FIG. 14-3 . This sequence differs from that in the first embodiment in that the VLAN ID to be disconnected is deleted from the internal connection management table. The L2GW  1003 - y  sets a “NOT USED” flag  15019232  for the VLAN ID to be disconnected, in the connection management table, as shown in  FIG. 15-3 . The L2GW reports the VLAN ID to be disconnected to another L2GW  1003 - 1 . The L2GW  1003 - 1  specifies in the internal VLAN ID management table that the reported VLAN ID is not used  15019232 , as shown in  FIG. 15-3 .  
       C. Third Embodiment  
       [0080]     The present invention can be applied when a PPPoE connection request is made by an untagged frame, without using the default VLAN, and when the network permits the transfer of the untagged VLAN frame, in the first or second embodiment. In that case, in the connection sequence, the PPPoE connection request is made by the untagged frame; the L2GW judges whether the connection can be made, in accordance with the terminal MAC address, Service Name, and other user information; not the session ID but the VLAN ID is sent to the user terminal; and the user terminal can communicate by a tagged VLAN frame having the assigned VLAN ID.  
         [0081]     For instance, the following processing is executed in a VLAN network system having a plurality of L2SWs serving a plurality of user terminals, a plurality of L2GWs serving the L2SWs, and a host network to which the L2GWs are connected.  
         [0082]     (1) The user terminal encapsulates a PADI packet in an untagged VLAN frame, broadcasts a connection request by the frame in accordance with the session establishment phase, and waits for a PADO packet.  
         [0083]     (2) When the untagged VLAN frame containing the PADI packet is received from the user terminal, the L2SW registers the user terminal address, waits for a PADO packet from an L2GW, and transfers the received tagged VLAN frame to an L2GW to which transmission is allowed.  
         [0084]     (3) When the untagged VLAN frame containing the PADI packet is received from the L2SW and when it is determined that the service name requested by the user terminal can be connected, the L2GW registers the transmission source user terminal address, waits for a PADR packet from the user terminal, and sends a tagged VLAN frame containing a PADO packet to the user terminal.  
         [0085]     (4) When the untagged VLAN frame received from the L2GW contains a PADO packet, when the transmission destination address is the user terminal address, and when a PADO packet has been waited for, the L2SW registers the transmission source L2GW address in association with the user terminal address, waits for a PADR packet, and transfers the received tagged VLAN frame to the user terminal.  
         [0086]     (5) When the untagged VLAN frame received from the L2SW contains a PADO packet, when the PADO packet has been waited for, and when the service name extracted from the packet has been registered, the user terminal registers the transmission source L2GW address, waits for a PADS packet, sends the tagged VLAN frame containing a PADR packet to the L2GW, and discards frames from another L2GW.  
         [0087]     (6) When the untagged VLAN frame received from the user terminal contains a PADR packet and when the transmission source address and transmission destination address extracted from the PADR packet match the registered addresses of the user terminal and L2GW, the L2SW waits for a PADS packet and transfers the received tagged VLAN frame to the L2GW.  
         [0088]     (7) When the untagged VLAN frame received from the L2SW contains a PADR packet and when the transmission source address extracted from the PADR packet matches the user terminal address in the PADR packet wait state, the L2GW obtains and registers the VLAN ID to be assigned to the user terminal, encapsulates a PADS packet having the assigned VLAN ID as a session ID in a tagged VLAN frame having the common VLAN ID, and sends the frame.  
         [0089]     (8) When the untagged VLAN frame received from the L2GW contains a PADS packet and when the transmission source address and transmission destination address extracted from the packet match the L2GW address and the user terminal address, the L2SW extracts the assigned VLAN from the PADS packet, enables transmission and reception of the tagged VLAN frame having the assigned VLAN ID with respect to the user terminal and L2GW, and transfers the received tagged VLAN frame to the user terminal.  
         [0090]     (9) When the untagged VLAN frame received from the L2SW contains a PADS packet and when the transmission source L2GW address is registered, the user terminal enables transmission and reception of a tagged VLAN frame having the assigned VLAN ID with respect to the L2GW and performs communication by using the assigned VLAN ID.  
         [0091]     According to the present invention, when a user terminal makes a connection request to a network, a variety of negotiation means such as the 802.1× protocol can be used, besides the PPPoE protocol.