Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) The synchronous hierarchy digital (SDH) is emergingthe as universal technology for transmission telecommunications in networks. the publication Since first of international standards by ITU-T in 1989, SDH equipment has been rapidly developedand deployed across the world,andisrapidlytakingoverfromitspredecessor,thePlesiochronousDigitalHierarchy (PDH).ThischapterdescribesSDHandtheNorthAmericanequivalentofSDH,SONET (SynchronousOpticalNetwork),fromwhichitgrew. | Networks and Telecommunications Design and Operation Second Edition. Martin P. Clark Copyright 1991 1997 John Wiley Sons Ltd ISBNs 0-471-97346-7 Hardback 0-470-84158-3 Electronic 13 Synchronous Digital Hierarchy SDH and Synchronous Optical Network SONET The synchronous digital hierarchy SDH is emerging as the universal technology for transmission in telecommunications networks. Since the first publication of international standards by ITU-T in 1989 SDH equipment has been rapidly developed and deployed across the world and is rapidly taking over from its predecessor the Plesiochronous Digital Hierarchy PDH . This chapter describes SDH and the North American equivalent of SDH SONET Synchronous Optical Network from which it grew. In particular the chapter describes the features of SDH which characterize its advantages over PDH. HISTORY OF THE SYNCHRONOUS DIGITAL HIERARCHY SDH The synchronous digital hierarchy SDH was developed from its North American forerunner SONET synchronous optical network . SDH is the most modern type of transmission technology and as its name suggests it is based on a synchronous multiplexing technology. The fact that SDH is synchronous adds greatly to the efficiency of the transmission network and makes the network much easier to manage. THE PROBLEMS OF PDH TRANSMISSION Historically digital telephone networks modern data networks and the transmission infrastructures serving them have been based on a technology called PDH Plesiochronous Digital Hierarchy as we discussed in Chapter 5. As we also discussed three distinct PDH hierarchies evolved as we summarize in Figure . They share three common attributes. 267 268 SYNCHRONOUS DIGITAL HIERARCHY AND SYNCHRONOUS OPTICAL NETWORK a Europe 64 2048 8448 34368 139264 564992 kbit s E1 E2 E3 hierarchy level 0 1 2 3 4 5 b North America 64 1544 6312 44 736 274176 kbit s DSO DS1 or T1 DS2 or T2 DS3 or T3 hierarchy level 0 12 3 4 c Japan 64 1544 6312 32 064 97 728 kbit s 1 hierarchy level 0 .
