Transmission in modern telecommunication networks is increasingly digital in nature, and the preferred transmission medium of choice is fiber optic. SONET standards are expected to provide transport infrastructure for global telecommunications for at least two or three decades. We most often hear about SONET rings, in which strands of fibers are stretched around a megalopolis in a ring configuration. The information is formatted into fixedlength cells. An asymmetric digital subscriber line (ADSL) is, in fact, a modem that uses a complex encoding scheme. This coding scheme permits transmission over copper wires pair at high speed. Currently, LEC uses ADSL as an access technology for their television business and for Internet access. 6
