1 channel pure video optical end machine (pair) 1 channel video optical end machine 1 channel 485 reverse data(pair) 2 channel pure video optical end machine(pair) 2 channel video optical end machine 1 channel 485 reverse data (pair) 2 channel pure video optical end machine (pair) 2 channel video optical end machine 1 channel 485 reverse data (pair) 2 channel pure video optical end machine (pair) 2 channel video optical end machine