ansmit all 32 volumes of the Encyclo- pedia Britannica in 1/10 second-the blink of an eye. That is an incredible speed. Not many people have a computer capable of capturing 10Gbps. Keep in mind that underlying all the various changes in telecommunications tech- nologies and infrastructures, a larger shift is also occurring-the shift from the electronic to the optical, or photonic, era. To extract and make use of the inherent capacity that fiber optics affords, we need an entirely new generation of devices that are optical at heart. Otherwise, we need to stop a signal, convert it back into an electrical form to pro- cess it through the network node, and then convert it back into optics to pass it along. (Conversion is discussed later in this chapter.) Consider a fax between Steve in the United States and his friend in Singapore. It begins as a piece of paper (analog). Steve's fax machine scans it (to digital). The modem in Steve's machine converts it (to analog). The Class 5 switch at Steve's local exchange converts it (to digital). The Class 4 switch in the United States converts it (to analog). The receiving Class 4 switch in Singapore converts it (to digital). The Class 5 switch at Steve's friend's local exchange converts it (to analog). The modem in the friend's fax machine converts it (to digital), and his fax machine prints it on paper (analog). That's eight conversions! Needing to make so many conversions will not allow us to exercise the high data rates we're beginning to envision. Given today's environment, for wireline facilities, it may be more appropriate to think of broadband as starting where the optical network infrastructure starts. Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) are part of the second generation of digital hierarchy, which is based on fiber optics as the physical infrastructure. (SDH and SONET are discussed in detail in Chapter 4.) The starting rate (i.e., the lowest data rate supported) on SDH/SONET is roughly 51Mbps. For the wireline technologies-thos