The SONET standard will establish a digital hierarchical network with a consistent worldwide transport scheme. SONET has been designed to take advantage of fibre, in contrast to the plain old telephone system which was designed for copper wires.
SONET carries circuit-switched data in frames at speeds in multiples of 51.84 megabits per second (Mbps) up to 48 * 51.84 Mbps = 2.488 gigabits per second. Since SONET uses multiple channels to transmit data, each SONET frame can be considered to be a two-dimensional table of bytes that is 9 rows high and 90 columns deep. For every OC-n level, SONET can transmit n number of frames at a given time. Groups of frames are called superframes.
SONET is the American version of SDH.
[Wulf Losee; Corporate Computing 8.92; STACKS; LAN Magazine 10.93].