etwork (MAN) of up to 100 km. When single-mode fiber is used, it has a core diameter of 8 to 10 um and a cladding diameter of 125 um. Thus, FDDI single-mode fiber is commonly specified as 8/125, 9/125, and 10/125. OPTICAL TRANSMITTER Available transmitters and receivers operate at 850, 1300, and 1550 nm; the 1300 nm wavelength is most com- monly used. Transmission at 850 and 1300 nm is designed for use over multimode fiber. Single-mode fiber that can support FDDI for greater transmission distances operate at 1300 and 1500 nm. Both lasers and laser diodes are used with multimode fiber; however, when single-mode fiber is used, the transmitter must be a laser diode since it has the narrow wavelength required to transmit optical signals into the narrow core of the fiber. ATTENUATION For multimode fiber the FDDI PMD standard speci- fies a power budget of 11.0 dB. Because the power budget of a system represents the minimum transmitter power and the minimum receiver sensitivity, this means that up to 11 dB of the optical signal can be lost. Fiber in the LAN In addition, the maximum cable attenuation is 1.5 dB/km at 1300 nm. When single-mode fiber is used, the PMD specifies a range of power budgets. The specified range depends on the types of transmitters used and extends from 10 to 32 dB (maximum). Media Interface and ST Connectors One of the well-thought-out portions of the ANSI standard is represent- ed by the FDDI Media Interface Connector (MIC). This connector, which is used to connect multimode fiber to an FDDI station, consists of a keyed plug and a keyed receptacle and is polarized to ensure that an appropri- ate transmitter/receiver-to-fiber association occurs, representing perhaps the first "dummyproof" optical connection. FDDI also supports ST-type connectors to physically connect optical fiber to an FDDI station. Although ST connectors provide a lower-cost alternative for connecting optical fiber to an FDDI station, they do not provide a polarized receptacle. Thus, when using an ST-type connector, you must en