The number of optical cores in an optical fiber is the total number of equipment interfaces multiplied by 2, plus 10% to 20% of the spare quantity, and if the communication mode of the equipment has serial communication and equipment multiplexing, you can reduce the number of cores. To see how many fibers there are, multiply the number of fibers by the multiple of the fibers. For example, 12 core fibers, 12*2=24 cores, 12 cores at the beginning and 12 cores at the end; 2. See link that shows top speeds per pair for fiber and Ethernet copper. Understanding Fiber Cores: Core: The central glass fiber that transmits light signals.