The present invention relates to an improved communications protocol which increases the efficiency of transmission in return channels on a multi-channel slotted Alohas system by incorporating advanced error correction algorithms, selective retransmission protocols and the use of reserved channels to satisfy the retransmission requests. Each of the central conductors includes a grounded leg portion which extends upward from a ground plate provided at the bottom surface of the ferrite along a side surface of the ferrite, which is bent at an upper ridge portion of the ferrite, and which extends on the top surface of the ferrite. The optical fiber means comprises either at least two single core optical fibers or a multicore optical fiber having at least two fiber cores. A program control reads the status byte from the memory and outputs a program enable signal in response thereto causing the clock generator to output the address latch in response to the program enable signal.