riers. Primarily because of the physical properties of embedded fiber, today there is a practical ceil- ing of 2.5 Gbps on many fiber networks, although there are instances where STM-64/OC-192 is also being deployed. Surprisingly, however, the time- division multiplexing (TDM) equipment installed today utilizes only a frac- tion of the intrinsic capacity of the fiber. Dense wavelength division multiplexing (DWDM) techniques were developed to address these issues. DWDM started to gain commercial success in the mid-1990s and achieved major deployment in the late 1990s. Up to now, the industry has focused to a large degree on the long-haul aspect of the business. However, metro edge and metro core needs have also arisen of late and are ill served by long-haul-retroftted solutions, which are too expensive for metro edge/metro access applications. Metro optical net- works and providers need to focus in another direction-namely, access. They need to capitalize on solutions (for example, coarse WDM [CWDM]) that are more cost effective in this space, where typical distances are one to four miles. Approximately 95 percent of the office buildings in the United States, not to mention the millions of other commercial buildings, are cur- rently not on fiber-based systems. Part of the issue relates to the cost of the in-building equipment. No one is going to make any money, much less the ill-informed venture capitalists and their investors, by deploying $80,000 to $150,000 of equipment in a building. Per-building equipment costs need to be in the $8,000 to $25,000 range for carriers to be able to deploy sustain- able services. 3.1.1 First-Generation Optical Networks As illustrated in Figure 3-1, a first-generation optical network is based on a ring architecture and uses SONET/SDH devices to transmit information Chapter 3 Figure 3-1 First-Generation Optical Network First-generation optical network. SONET SONET SONET Growth SONET S[SONET switch switch SONET Working Fiber Ring [SONET SONET Protection Ring SONET SONET over fiber. 