IBDN standard suggests using 12-core cables for communication rooms within buildings and 24-core cables for main distribution rooms, which can serve as a practical starting point for your selection. 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. This post will guide you through understanding fiber optic cores and selecting the perfect cable for your needs. Understanding Fiber Cores: Core: The central glass fiber that transmits light signals. Single-mode: A. Two popular types of optical fiber cables are 8-core optical cable and 12-core single-mode indoor fiber optic cable.