Transcription of SDH, SONET and PDH - 高雄應用科技大學
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SDH, SONET and PDH - 高雄應用科技大學
By Othmar KyasAn Agilent Technologies PublicationNetworkTroubleshootingAgilent TechnologiesSDH, SONET and PDH14 SDH, SONET and PDH14 Most problems are either unimportant or impossible to solve. VICTOR SDH, SONET and PDH:Specification and ImplementationBack in the late 70s, Bellcore (now Telecordia) saw the need to replace thePlesiochronous (near synchronous) Digital Hierarchy (PDH) in the North Ameri-can Bell System (as it was then known) with a new synchronous started work on what we now know as SONET , the Synchronous OpticalNETwork. PDH networks had evolved in a rather ad hoc manner and it was timeto improve on this. A transmission standard was needed that allowed higher ratetransmission, properly planned network management facilities and, most im-portantly, a means to time lock the digital channels being carried so thatindividual lower rate channels could be accessed directly without the need tobreak down the PDH signal by hierarchy level, taking into account the justifica-tion (stuffing) that had occurred at each level during signal construction.
487 SDH, SONET AND PDH 14 SECTION III TROUBLESHOOTING WIDE-AREA NETWORKS past few years. All PDH multiplex hierarchies can also be transmitted over the SDH/SONET network, so that the transition from PDH to SDH/SONET is smooth.
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