Patent ID: 7171504

Claim:
A transmission unit for use in a network where the transmission unit is connected with a peer transmission unit by at least first and second lines, the transmission unit comprising: a first layer- 2 bridge having at least a first bridge port; a second layer- 2 bridge having at least a second bridge port; first and second physical ports for sending and receiving frames via the first and second lines, respectively; a bridge port state monitoring section monitoring at least the first bridge port; a switching section providing cross connections between the first and second physical ports and the first and second bridge ports; a port correspondence table defining the cross connections in the switching section; a port correspondence table managing section that initially configures the port correspondence table so as to connect the first and second physical ports respectively to the first and second bridge ports, and reconfigures the port correspondence table so as to remove the connection between the first physical port and the first bridge port and add a connection between the first physical port and the second bridge port when the bridge port state monitoring section detects a transition of the first bridge port from a non-blocked state to a blocked state as a result of spanning-tree protocol processing in the second layer- 2 bridge.