ice (POTS) remains the cash cow in the industry. In these final sections we'll explain T- and E-Carrier, SONET, SDH, and voice digitization techniques. Conserving Bandwidth: Voice Transport The original voice network, including access, transmission facilities, and switching components, was exclusively analog until 1962 when T-carrier emerged as an intra-office trunking scheme. The technology was origi- nally introduced as a short-haul, four-wire facility to serve metropolitan areas and was a technology that customers would never have a reason to know about-after all, what customer could ever need a meg-and-a-half of bandwidth? Over the years, however, it evolved to include coaxial cable facilities, digital microwave systems, fiber, and satellite, and of course became a premier access technology that customers knew a great deal about. Consider the following scenario: A corporation builds a new head- quarters facility in a new area just outside the city limits. The building will provide office space for approximately 2,000 employees, a consider- able number. Those people will need telephones, computer data facilities, fax lines, videoconferencing circuits, and a variety of other forms of con- nectivity. The telephone company has two options that it can exercise to provide access to the building. It can make an assessment of the number of pairs of wire that the building will require and install them, or it can do the same assessment but provision the necessary bandwidth through carrier systems that transport multiple circuits over a shared facility. Obviously, this second option is the most cost-effective and is, in fact, the option that is most commonly used for these kinds of installations. This model should sound familiar: Earlier we discussed loop carrier systems and the fact that they reduce the cost of provisioning network access to far-flung neighborhoods. This is the same concept; instead of a residential neigh- borhood, we're provisioning a "corporate neighborhood." Downloaded from Digital Engineering Libra