 cost effective in this context. Having established a reality check on the baseline demand and market for this technology in both the long haul and metro space to address the industry hype, we can now proceed with a more technical discussion. Dense Wavelength Division Multiplexing (DWDM) Systems SONET SONET Figure 5-8 Optical Line Amplifier SONET SONET SONET SONET SONET SONET 5.2 Overview of Technology 5.2.1 TDM Evolution Going back at least half of a century, network designers have looked for sim- ple, straightforward methods for the migration of networks to higher per- formance levels. Throughout the 1950s and 1960s, first analog and then digital carrier systems of ever-increasing capacity were being developed. A carrier system is a multiplexed transmission system supporting multiple channels. Fiber-optic (lightwave) systems have been deployed since at least 1979 (one such system that operated at DS3 rates was deployed in Trum- bull, Connecticut, in October 1979). As early as 1983, 90-Mbps systems (FT3C) were deployed. In the mid to late 1980s, systems supporting 400 to 565 Mbps emerged, followed by systems operating at 800 to 1,100 Mbps. In the early 1990s, systems operating at 1,600 to 2,200 Mbps (1.6 to 2.2 Gbps) emerged. Finally, SONET/SDH systems emerged supporting up to 2.5 Gbps (OC-48); 10-Gbps (OC-192) systems have been introduced in the past cou- ple of years, and 40-Gbps systems are under development. These advances are based on TDM technologies, where the clock driving the on/off intensity modulation (IM) light process is driven at a higher pulse rate. At the limit of how short the light pulse can be made, there are at least two other methods to increase carrying capacity on the fiber waveguide: coherent transmission, which is a variant of full FDM, and WDM, which is in effect a space-division multiplexing method where distinct light beams are modulated with IM methods, as shown in Figure 5-9. Although coherent methods offer perhaps the best long-term opportunity for maximum Chapter 5 Expansion Port 