 or writing about the subject. The confusion is not SO much a matter of the function as it is the nature and character of what is actually being switched and the mechanics of the switching process taking place. Fundamentally, switching enables a full or part-time fixed bit rate transmission facility to be shared. CROSS-CONNECT SWITCHING Cross-connect switching is almost exclusively a telephone company term and function. It's nothing more than an electronic version of a manual patch panel. It is used to groom bandwidth and provide private or leased-line facilities. Its formal name is digital access and cross connect switch (it is also referred to as digital access and cross- connect system) and, as you might guess, it has been given acronyms: DCS and DACS. There are several types of DCS. The earliest DCS simply enabled connection of a DS-0 segment of bandwidth or time slot from one DS-1 facility to another inside wire centers and central offices. As higher order multiplexing equipment became available, more DCS functionality appeared and enabled switching of not only DS-0 level circuits, but also whole DS-1 circuits across multiple DS-2 or DS-3 facilities. SONET/SDH DCS has several capabilities, including grooming band- width at DSO (64 Kbs) up through all the VT levels and the STS level (51 Mbs). For instance, it is possible to cross-connect a 64 Kbs segment from one VT into another VT on a different STS in the same or another 4 NETWORK TECHNOLOGY AND METHODOLOGY OC level. It is also possible to cross-connect an entire 51 Mbs STS in one lambda to a different lambda on another path or route. CIRCUIT SWITCHING Circuit switching and routing is the basis for all domestic and inter- national telephone or voice grade, dial-up traffic. The circuit switch- ing function is distributed between end-office switching systems and network switching systems. End office switching systems may be a private branch exchange (PBX) physically located on subscriber premises, or a partition in the telephone company's nearest office, comm