Design of DS 1 Transport Device in SDH Network ∗
نویسنده
چکیده
Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) are the standards for lightwave transmission systems, which can accommodate various existing signal types via Tributary Units (TUs) or Virtual Tributaries (VTs). In the SDH standards, Tributary Unit-11 (TU-11) is used to transport the DS1 signal with payload pointer and path overheads. In this paper, asynchronous floating mode TU11 Mapper is designed by FPGAs for transmit and receive devices. The DS1 signal is mapped into TU-11 frame, and through 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 direction, a synchronizer with efficient stuffing algorithm is designed to minimize the waiting time jitter and absorb the frequency offset, the instantaneous jitter, the wander, and the gap of TU-11 data payload. In the drop direction, a desynchronizer implemented by a novel all digital phase locked loop 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 embedded in an STM-1 ADM system for long term testing. key words: SDH, SONET, DS1, TU-11 mapper, FPGA
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