The RFL Fiber Service Unit (FSU) provides an interface between synchronous electrical signals and optical fiber. It can be used with the RFL 9300, RFL 9745, RFL IMUX 2000 or other types of multiplexers. It can also be used with any other C37.94 compliant, end device. There are a total of five varieties of FSUs using both single and multimode fiber heads. They use RS-449, V.35, G.703, X.21 and E1 as inputs and outputs on the non-fiber side of the connection. Note that there is a modification allowing the unit to be mounted into a 1U Chassis. The FSU is a stand-alone device, which is essentially a translator to and from data sent using these five interface standards in accordance with the IEEE C37.94 fiber protocol. The G.703 is 64,000 bps only and thus it has N fixed at 1. The other four versions use a DIP switch to set the value of N.