Patent ID: 8139584

Claim:
A frame transmission device having a port to transmit and receive a frame and a learning table to store a transmission source address included in the frame received at the port and the receiving port in association with each other, comprising: a port detector to detect whether learning data coincident with the transmission source address included in the frame received at the port is stored in the learning table; a port judging unit to compare a port learned in the learning data and detected by the port detector to the receiving port; a loop judging unit to judge on a basis of a time lapse from the storage of the learning data whether the frame is in a loop or not when the port learned in the learning data is not coincident with the receiving port as a comparison result of the port judging unit, wherein when the time lapse is less than a given value, the loop judging unit judges that the frame is in a loop, and discards the frame a discard table storage unit to store a transmission source address corresponding to a frame, ID information of the port receiving the frame, and a time at which the frame is discarded by the loop judging unit; and a discard judging unit to judge on the basis of the transmission source address of the received frame, the port receiving the frame, and the discard table whether the frame should be discarded; and a loop eliminating judging unit to detect a transmission source address in which a transmission source address stored in the learning table is coincident with a transmission source address stored in the discard table, and judging whether the loop of the frame is eliminated, on the basis of a time at which the detected transmission source address is stored in the discard table and a time at which the transmission source address is stored in the learning table.