A simple rule is that each device needs two cores—one for sending and one for receiving data. Two popular types of optical fiber cables are 8-core optical cable and 12-core single-mode indoor fiber optic cable. Of course, this is a general situation, and specific words may consider according to the following criteria. Number of wiring points and switches. The total number of cores for a 1pc fiber patch cable is calculated as the number of branches multiplied by the number of cores per branch (if there are no branches, the number of branches = 1). First, clearly understand the number of wiring points, and calculate. Single-mode fiber optic cables single-mode fiber optic cables 1 have a small core, typically around 9µm, and are designed to carry signals over long distances at higher bandwidths. They use OS1 or OS2 OS1 or OS2 classifications to.