Multiplexers make one line carry many conversations: fiber multiplexers that combine several data streams onto a single strand, wavelength-division systems that multiply the capacity of fiber already in the ground, and the managed chassis units that aggregate serial and Ethernet feeds across campuses and between buildings. When pulling new fiber is the expensive option, a multiplexer is usually the cheaper one.
Design from the circuit inward: what the two ends must exchange, over what distance, on what fiber type - single-mode and multimode are different worlds, and optics are distance-rated. Multiplexers deploy in matched pairs or as modules in a compatible chassis, so both ends belong on one order. Managed models earn their premium on links that matter, since a dark unmanaged box tells no one why the building dropped. COLAMCO quotes multiplexers and optical transport for business, government, and education networks, matched to the fiber plant they will ride.