PDHSONETSDH

PDHSONETSDH refers to the integration of Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SDH) technologies. PDH systems, originating in North America and Japan, use different framing structures and bit rates, making direct interworking challenging. SDH, on the other hand, developed in Europe and internationally, offers a standardized, hierarchical multiplexing scheme. The term PDHSONETSDH acknowledges the need to interface these two distinct but related digital transmission hierarchies.

SDH was designed to overcome the limitations of PDH, providing greater flexibility, efficiency, and management capabilities. It introduced standardized multiplexing structures and a common framing format, allowing for easier network upgrades and interconnections. However, many existing networks relied on PDH equipment. Therefore, interfaces and conversion mechanisms were developed to allow PDH signals to be transported over SDH networks and vice versa.

The SONET component of the term, Synchronous Optical NETworking, is the North American equivalent of SDH. While conceptually similar in their synchronous nature and hierarchical organization, SONET and SDH have differences in their overhead bytes and specific frame structures. Consequently, the term PDHSONETSDH also implicitly covers the need for interworking between PDH and SONET, as well as between SONET and SDH, and across all three. Network operators often had to manage environments containing a mix of these technologies, necessitating equipment and procedures for their seamless integration and interoperation.