p is required, then the "call" is handed up to IP, which takes whatever steps are required to perform the lookup (a DNS request, for example). Once it has the information, it hands it down to ATM, which proceeds to set up the call. The next time the two need to communicate, ATM will be able to handle the connection. There are other services looming on the horizon in which ATM plays a key role, including wireless ATM and video-on-demand for the deliv- ery of interactive content such as videoconferencing and television. This leads to what I often refer to as "the great triumvirate": ATM, SONET or SDH, and broadband services. By combining the powerful switching and multiplexing fabric of ATM with the limitless transport capabilities of SONET or SDH, true broadband services can be achieved, and the idea of creating a network that can be all things to all services can finally be realized. Optical Networking Optical networking is often viewed as a point-to-point technology. It has achieved such a position of prominence in the last 2 years, however, that it qualifies as a transport option in its own right. Furthermore, optical 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 Figure 7-14 photophone transmitter switching is fast becoming real and optical routing is not far behind. In this next section, we discuss the development of optical networking, the various technologies that it employs, and the direction it seems to be going in this fast-paced market. Early Optical Technology Breakthroughs In 1878, 2 years after perfecting his speaking telegraph (which became the telephone), Alexander Graham Bell created a device that transmitted the human voice through the air for distances up to 200 meters. The device, which he called the photophone, used carefully angled mirrors to reflect sunlight onto a diaphragm that was at