Patent ID: 7885196

Claim:
A loop communication system comprising: a plurality of communication devices, wherein each respective communication device of the plurality of the communication devices holds an identification data assigned to said respective communication device, and has a single port used for transmission and reception of a data packet, and which plurality of the communication devices are connected by using said single port of each of the plurality of the communication devices to constitute an IEEE-based port synchronization type network of a loop structure, and wherein said data packet from each of said plurality of communication devices is transferred on said network of said loop structure in one direction, wherein each of said plurality of communication devices comprises: a transmission/reception control circuit; a single connector connected to two of said plurality of communication devices through first and second cables; and a beta port connected between said transmission/reception control circuit and said connector and configured to transfer said data packet received through said first cable and said connector to said transmission/reception control circuit and to transfer said data packet received from said transmission/reception control circuit onto said second cable through said connector, wherein in said communication device, said transmission/reception control circuit receives said data packet from an upstream one of said plurality of communication devices through said first cable, said connector and said beta port, determines whether an identification data contained in said data packet is coincident with said held identification data and discards said data packet when the contained identification data is identical to said held identification data, wherein the identification data contained in said data packet is identification data of a transmitter of the data packet, wherein said communication device comprises: a link layer control circuit configured to generate and send a data prefix and a data end of the data packet to said transmission/reception control circuit when said data packet should be transmitted to a destination communication device; and an application/transaction control circuit configured to generate and send said data packet to said transmission/reception control circuit when said data packet should be transmitted to a destination communication device, and said transmission/reception control circuit adds said held identification data after said data prefix of said data packet and transmits the data prefix to which said held identification data is added, said data packet, and said data end sequentially to a downstream one of said plurality of communication devices through said beta port, said connector and said second cable.