Use duplex multimode or singlemode fiber optic cable for applications that require simultaneous, bi-directional data transfer. Workstations, fiber switches and servers, fiber modems, and similar hardware require duplex cable. Duplex Duplex cable consists of two fibers, usually in a zipcord (side-by-side) style. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be. Simplex and duplex are different kinds of communication channels in telecommunications and computer networking, which provide pathways to convey information. One end is the. ISO/IEC 11801 defines the OM1, OM2, OM3, OM4, and OM5 types of multimode fiber.