SONET is a high-speed fiber-optic
wide area network
. On the OSI
model, it is part of the physical layer. Bell Labs developed the American
version of SONET, which incorporated the ITU standard Synchronous Digital Hierarchy
(SDH). In the United States, the system is called SDH-SONET, in Europe it ia called SDH-Europe, and in Japan it is called SDH-Japan. The differences arise out of the configuration and implementation of local telephone services.
SONET can work with mesh or ring network topologies. It provides point-to-point communications similar to FDDI. To increase the bandwidth of the system, Time Domain Multiplexing (TDM) is used.
Starting rates for SONET begin at 51.84Mbps and go up in multiples of this speed. Speed ratings for SONET are expressed on the OC scale. The higher the rating, the more optical channels are available. With such a wide bandwidth and high speed, large city-wide SONET rings can be constructed to transport video, movies, sound and imaging. SONET can carry data more efficiently than tradition broadband cable installations. The initial construction costs and equipment can be daunting, but institutions may save money in the future by expanding resources. An example of this is the SONET ring being developed for the colleges of Colorado. Full-motion video-on-demand can broadcast classes and on-line courses. Libraries can share multiple copies of books. Radio stations can broadcast perfect digital audio.