A review of the four major SONET/SDH rings

With ever increasing bandwidths being transported over fiber optic cables, both buried and suspended from poles, rings have become the principal means of providing self healing transport networks. A review is given of the four major ring types that are currently deployed, under development, being defined, or are for further study. These ring types are the unidirectional path switched ring, four-fiber bidirectional line switched ring, two-fiber bidirectional line switched ring, and the unidirectional line switched ring.<>