and disadvantages associated with its use that are application-depen- dent. These features should be carefully considered if you are designing a system instead of purchasing an electricooptical system, as the latter includes light source, coupler, connector, and fiber as a single entity. CHAPTER Fiber in the LAN Chapter Five In this chapter we discuss the use of transmission over fiber-optic media in the local area network (LAN) environment. Because the use of optical fiber in a LAN dates to the early 1980s with the introduction of the Fiber Distributed Data Interface (FDDI) standard, we will begin our examination of fiber in the LAN with a brief examination of FDDI. Although FDDI is relatively expensive and is considered by many per- sons to be obsolete because of the low availability of low-cost Fast Ether- net and the reduced cost of Gigabit Ethernet, to paraphrase Mark Twain, rumors of its death have been greatly exaggerated. FDDI uses a token-passing scheme which provides a data transfer capability that approaches 90 percent of its 100-Mbits/s operating rate, while lower-cost Fast Ethernet in a shared media environment will have collisions because of its design, which reduces practical throughput considerably under 100 Mbits/s. Once we examine FDDI, we will turn our attention to Ethernet and Fast Ethernet, examining the use of fiber in both net- work environments. We will then conclude this chapter with a discus- sion of Gigabit Ethernet. Fiber Distributed Data Interface (FDDI) The FDDI standard dates to October 1982, when the American National Standards Institute (ANSI) Committee X3T9.5 was chartered to develop a high-speed data networking standard. The resulting effort was the devel- opment of a token-passing optical fiber media network based on the use of two fiber pairs, each operating at 100 Mbits/s. Position in the OSI Reference Model FDDI is defined as the two bottom layers of the seven-layer Internation- al Systems Organization (ISO) Open System Interconnection (OSI) Refer- ence Model: the physical a