er with wavelength di- vision multiplexing (WDM) techniques will find fiber optics competing with microwave for high-bandwidth, long-distance trans- mission applications. WDM especially will come into play as com- munications suppliers continue to lean towards supplying broadband THE MEDIUM AND THE MARKET 13 services to subscribers, such as video and data. With WDM, multiple optical signals may be transmitted over different wavelengths within a single optical fiber. WDM is accomplished by optically combining outputs of several light sources, each operating at a different wavelength or color, and coupling the composite signal into an optical fiber. An optical split- ter, or demultiplexer, at the receiving end of the link separates the various wavelengths or colors and channels them into separate re- ceivers. Because the different color light signals travel through the fiber independently, each represents a high-bandwidth transmission channel. WDM is expected to be used on a regular commercial basis by the mid-1980's. 1.4 A VIEW FROM THE BUSINESS SIDE The telecommunications market is an eight billion dollar market with expected growth to thirteen billion dollars by 1985. The protion of the communication market composed of large (Fortune 500/50) companies represents 40% of the total business communications market. This large company market is changing at a higher rate than most other major segments of the communication market. These changes include high growth in some segments of the market as well as high levels of equipment upgrades in other segments. Within this market, significant business opportunities are created. The primary key to the market is providing user controls. The driving force behind most of the network changes is the users' desire for control. Control includes network management, maintenance, and user access control. A major result of these changes is that the fastest-selling products in the market incorporate network control capabilities. These include call detail recording systems in voice net- 