Network relay system and control method thereof

Abstract

The network relay device of the invention makes a pair with at least a specific network device to relay data in a network. The network relay device includes: a control module that sends and receives a control frame signal to and from the specific network device, selects either of a master mode and a backup mode based on at least the control frame signal sent from the specific network device, and changes a working state according to a result of the selection; and a communication module that is under control of the control module to open a port and enable data transmission via a line linked to the port in the case of setting a master state to the working state, and to block off the port and disconnect the line linked to the port in the case of setting a backup state or another non-master state to the working state. The control module changes the working state from the backup state to a first intermediate state in response to selection of the master mode, determines whether the specific network device is in the backup state, based on the control frame signal sent from the specific network device, and changes the working state from the first intermediate state to the master state after confirmation that the specific network is in the backup state.

1 . A network relay device that makes a pair with at least a specific network device to relay data in a network, the network relay device comprising: 
 a control module that sends and receives a control frame signal to and from the specific network device, selects either of a master mode and a backup mode based on at least the control frame signal sent from the specific network device, and changes a working state according to a result of the selection; and    a communication module that is under control of the control module to open a port and enable data transmission via a line linked to the port in the case of setting a master state to the working state, and to block off the port and disconnect the line linked to the port in the case of setting a backup state or another non-master state to the working state,    the control module changing the working state from the backup state to a first intermediate state in response to selection of the master mode, determining whether the specific network device is in the backup state, based on the control frame signal sent from the specific network device, and changing the working state from the first intermediate state to the master state after confirmation that the specific network is in the backup state.    
   
   
       2 . A network relay device in accordance with  claim 1 , wherein the control module changes the working state from either of the backup state and the first intermediate state to a second intermediate state in the event of failed reception of the control frame signal from the specific network device for a preset time period, 
 in the case of subsequent resuming reception of the control frame signal from the specific network device, the control module selecting either of the master mode and the backup mode and changing the working state from the second intermediate state to the first intermediate state in response to selection of the master mode, while changing the working state from the second intermediate state to the backup state in response to selection of the backup mode.    
   
   
       3 . A network relay device in accordance with  claim 2 , wherein the control module changes the working state from the second intermediate state to the master state, in response to an externally given transition instruction to the master state.  
   
   
       4 . A network relay device in accordance with  claim 3 , wherein the network includes a large number of virtual LANs, which are divided into multiple groups, 
 the control module carries out selection of either of the master mode and the backup mode and management of the working state with regard to each of the multiple groups, and    the communication module under control opens and blocks off the port with regard to each of the multiple groups.    
   
   
       5 . A network relay device in accordance with  claim 1 , wherein the network includes a large number of virtual LANs, which are divided into multiple groups, 
 the control module carries out selection of either of the master mode and the backup mode and management of the working state with regard to each of the multiple groups, and    the communication module under control opens and blocks off the port with regard to each of the multiple groups.    
   
   
       6 . A network relay device in accordance with  claim 2 , wherein the network includes a large number of virtual LANs, which are divided into multiple groups, 
 the control module carries out selection of either of the master mode and the backup mode and management of the working state with regard to each of the multiple groups, and    the communication module under control opens and blocks off the port with regard to each of the multiple groups.    
   
   
       7 . A control method of controlling a network relay device that makes a pair with at least a specific network device to relay data in a network, the control method comprising the steps of: 
 (a) sending and receiving a control frame signal to and from the specific network device, selecting either of a master mode and a backup mode based on at least the control frame signal sent from the specific network device, and changing a working state according to a result of the selection; and    (b) opening a port and enabling data transmission via a line linked to the port in the case of setting a master state to the working state, while blocking off the port and disconnecting the line linked to the port in the case of setting a backup state or another non-master state to the working state,    the step (a) comprising the steps of:    (a-1) changing the working state from the backup state to a first intermediate state in response to selection of the master mode, and determining whether the specific network device is in the backup state, based on the control frame signal sent from the specific network device; and    (a-2) changing the working state from the first intermediate state to the master state after confirmation that the specific network is in the backup state.    
   
   
       8 . A control method in accordance with  claim 7 , wherein the step (a) further comprises the steps of: 
 (a-3) changing the working state from either of the backup state and the first intermediate state to a second intermediate state in the event of failed reception of the control frame signal from the specific network device for a preset time period,    (a-4) in the case of subsequent resuming reception of the control frame signal from the specific network device after the step (a-3), selecting either of the master mode and the backup mode and changing the working state from the second intermediate state to the first intermediate state in response to selection of the master mode, while changing the working state from the second intermediate state to the backup state in response to selection of the backup mode.    
   
   
       9 . A control method in accordance with  claim 8 , wherein the step (a) further comprises the step of: 
 (a-5) changing the working state from the second intermediate state to the master state, in response to an externally given transition instruction to the master state.