With the emergence of high-speed optical transmission, the pre-existing plesiochronous digital hierarchy (PDH) appeared unsuitable for achieving network synchronization, leading to the development of the synchronous optical network (SONET) and synchronous digital hierarchy (SDH) as the two equivalent standards for circuit-switched optical networks. Several bandwidth-efficient techniques were also developed to carry packet-switched data traffic over SONET/SDH networks, offering some useful data-over-SONET/SDH architectures. Subsequently, with the increasing transmission rates for SONET/SDH and Ethernet-based LANs, a convergent networking platform called optical transport network (OTN), was developed. With the ever-increasing volume of bursty data traffic, a standard for packet-switched ring networks, called resilient packet ring (RPR), was also developed for better bandwidth realization in optical fibers. In this chapter, we first present the SONET/SDH networks and the techniques for supporting the data traffic therein, followed by a description of the basic concepts and salient features of the OTN and RPR networks. (147 words)
