ht distribution in a fiber. Other topics covered in Chapter 3 include a brief introduction to the increased trans- mission capacity of a fiber through wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM). Light Sources and Detectors Like any type of transmission system, an optical transmission system requires a transmitter and a receiver. The transmitter is the light source; the receiver is an optical detector, also referred to as a photodetector. Thus, in Chapter 4 we will describe the operation of light-emitting diodes (LEDs) and lasers as well as different types of optical detectors. Fiber in the LAN Beginning in Chapter 5, we discuss applications that use optical transmis- sion systems. In that chapter we will examine the use of optical transmission in the local area network, investigating how one version of Fast Ethernet and several versions of Gigabit Ethernet are dependent on the use of fiber. In addition, we will also summarize the functions of the fiber channel, which enables high-speed access between computers and data storage and represents the cornerstone of storage area network communications. Fiber in the WAN Once we discuss the practical use of fiber in the local area network, we will focus on the wide area network. In Chapter 6 we will discuss and describe the Synchronous Optical Network (SONET) and its European counterpart, the Synchronous Digital Hierarchy (SDH). We will also examine WDM and DWDM in more detail and an evolving technology referred to as the Internet Protocol (IP) over SONET. Introduction Fiber in the Neighborhood The growth in the use of digital subscriber line (DSL) and cable modems requires telephone companies and cable operators to route fiber into neighborhoods to satisfy the increased transmission requirements of subscribers. Thus, in Chapter 7 we will examine the technology that we can collectively refer to as fiber to the neighborhood. Fiber in the Building No book covering optical transmission components would be complete without discus