Design of DS1 transport device in SDH network

Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) are the standards for lightwave transmission systems, which can accommodat e Various existing signal types via Tributary Units (TUs) or Virtual Tribut aries (VTs). In the SDH standards, Tributary Unit-ii (TU-11) is used to tra nsport the DS1 signal with payload pointer and path overheads. In this pape r, asynchronous floating mode TU-11 Mapper is designed by FPGAs for transmi t and receive devices. The DS1 signal is mapped into TU-11 frame, and throu gh Combus interface, then directly added/dropped into/from the VC-4 payload by taking advantage of the byte order frame format of SDH. In the add dire ction, a synchronizer with efficient stuffing algorithm is designed to mini mize the waiting time jitter and absorb the frequency offset, the instantan eous jitter, the wander, and the gap of TU-11 data payload. In the drop dir ection, a desynchronizer implemented by a novel all digital phase locked lo op and FIFO is used to accommodate the effect of irregular spacing of frame format and jitters generated by the pointer movement and bit justification . A prototype circuit board is built with the designed TU-11 Mapper and emb edded in an STM-1 ADM system for long term testing.