Communication system linking between user terminals, and user terminal connecting unit and communication method used in same communication system

A user terminal connecting unit for transmitting and receiving communication data to/from directed user terminals among a plurality of user terminals and for transmitting and receiving communication data among a user terminal connecting unit and all of other user terminal connecting units via a communication line:

• wherein the user terminal connecting unit converts the communication data from the directed user terminals into a signal light to be transmitted having a wavelength unique to each of the user terminal connecting units and transmits the signal light to all of other user terminal connecting units via the communication line;
• and while converting transmission/reception information showing a transmission/reception status of the communication data in the user terminal connecting unit into a control light having a predetermined wavelength different from a wavelength of the signal light to be transmitted and transmitting the control light to all of other user terminal connecting units via the communication line at a predetermined timing set uniquely to the user terminal connecting unit, receives the signal light and the control light via the communication line, converts the control light into the transmission/reception information directed to each of the user terminal connecting units, selects each of the signal lights based on the transmission/reception information and converts the selected signal light into communication data, transmits the communication data to a corresponding user terminal, and controls transmission of the signal light based on the transmission/reception information.

A communication method used in a communication system linking between user terminals comprising a plurality of user terminal connecting units for transmitting and receiving communication data to/from directed user terminals among a plurality of user terminals and for transmitting and receiving the communication data between one user terminal connecting unit and all of other user terminal connecting units and a communication line for transmitting and receiving the communication data between the user terminal connecting units:

• wherein each of the user terminal connecting units converts the communication data from the directed user terminals into a signal light to be transmitted having a wavelength unique to each of the user terminal connecting units and transmits the signal light to all of other user terminal connecting units via the communication line;
• and while converting transmission/reception information showing a transmission/reception status of the communication data in the user terminal connecting unit into a control light having a predetermined wavelength different from a wavelength of the signal light to be transmitted and transmitting the control light to all of other user terminal connecting units via the communication line at a predetermined timing set uniquely to each of the user terminal connecting units, receives the signal light and the control light from another user terminal connecting unit via the communication line, converts the control light into the transmission/reception information directed to each of the user terminal connecting units, selects each of the signal lights based on the transmission/reception information and converts the selected signal light into the communication data, transmits the communication data to a corresponding user terminal, and controls transmission of the signal light based on the transmission/reception information.