The Synchronous Digital Hierarchy (SDH)

Publisher Summary The synchronous digital hierarchy (SDH) is a new standard for multiplexing together many low rate digital traffic channels into higher rate channels in order that these low rate channels may be more efficiently transported around a telecommunications network. Due to the business pressures confronting the world's public telecommunications operators, SDH has developed into a comprehensive set of standards which address all aspects of a telecommunications transport network. As with plesiochronous digital hierarchy (PDH), SDH is designed to transport isochronous traffic channels and is focused very much on layer one of the well known ISO seven layer OSI protocol hierarchy. Again, like PDH, SDH is based on a hierarchy of continuously repeating, fixed length frames. The effects of the full range of SDH standards will probably be felt over a much wider area of telecommunications because of their general applicability. For example, the mere existence of the SDH optical interface specifications will probably lead to their use in a variety of non-SDH applications, simply because there is a dearth of competing standards.