Simplex vs. duplex fibre patch cable.
Multimode and single-mode patch cables can be simplex or duplex.
Simplex has one fibre, while duplex zipcord has two fibres joined with a thin web. Simplex (also known as single strand) and duplex zipcord cables are tight-buffered and jacketed, with Kevlar® strength members. Because simplex fibre optic cable consists of only one fibre link, you should use it for applications that only require one-way data transfer. For instance, an interstate trucking scale that sends the weight of the truck to a monitoring station or an oil line monitor that sends data about oil flow to a central location.
Use duplex multimode or single-mode fibre optic cable for applications that require simultaneous, bidirectional data transfer. Workstations, fibre switches and servers, Ethernet switches, backbone ports, and similar hardware require duplex cable.