A simple rule is that each device needs two cores—one for sending and one for receiving data. Fiber cores are the heart of fiber optic cables, transmitting light signals that carry data. Of course, this is a general situation, and specific words may consider according to the following criteria. Number of wiring points and switches. In terminal boxes and closures, core count is directly related to: Common configurations include: These configurations do not represent performance differences, but rather. Common fiber cores include 1 core, 2 cores, 6 cores, 8 cores, etc.