 days of data net- working, dedicated facilities were created by manually patching the end points of a circuit at a patch panel, thus creating a complete four-wire cir- cuit. Beginning in the 1980s, digital cross-connect devices such as AT&T's Digital Access and Cross-Connect (DACS) became common, replacing the time-consuming, expensive, and error-prone manual Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Chapter 7 process. The digital cross-connect is really a simple switch, designed to establish "long-term temporary" circuits quickly, accurately, and inex- pensively. Enter the world of optical networking Traditional cross-connect sys- tems worked fine in the optical domain, provided there was no problem going through the O-E-O conversion process. This, however, was one of the aspects of optical networking that network designers wanted to erad- icate from their functional requirements. Thus was born the optical cross-connect switch. The first of these to arrive on the scene was Lucent Technologies' LambdaRouter. Based on a switching technology called Micro Electrical Mechanical System (MEMS), the LambdaRouter was the world's first all-optical cross-connect device. The product has since been discontinued, but the technology remains a good illustration of optical switching. MEMS relies on micro-mirrors, an array of which is shown in Figure 7-25. The mirrors can be configured at various angles to ensure that an incoming lambda strikes one mirror, reflects off a fixed mirrored surface, strikes another movable mirror, and is then reflected out an egress fiber. The LambdaRouter and other devices like it offered switching speed, a relatively small footprint, bit rate and protocol transparency, nonblock- ing architecture, and highly developed database management. Funda- mentally, these devices are very high-speed, high-capa