DH and SONET, which are described in Chapter 10. Recently there have been a number of discussions about whether SDH/SONET deploy- ment is now in decline and soon to be phased out of operators' networks in favor of packet optical transport systems with Wavelength Division Multiplexed (WDM) interfaces. It is worth spending a few moments reflecting on this possibility by analyzing the market share and trend of packet- and circuit-switched optical equipment to put such comments into perspective. According to Infonetics Research, sales of optical network hardware increased consistently in the four years from 2003 to 2007 to a total worldwide market value of $13.9 billion-a 19 percent jump from 2006. Although a billion-dollar market, the packet optical transport systems market is growing because of the rapid increase in consumer and business packet-based services Chapter 11 Next Generation Synchronous Digital Hierarchy transporting voice, video, and data across converged IP infrastructures. The remaining $12.9 billion market share is in WDM and SDH/SONET transport equipment. Although the spending trend now appears to be shifting toward the area of WDM equipment (29 percent growth in 2007) compared with SDH/SONET (9 percent growth in 2007), SDH/ SONET accounts for 61 percent of worldwide optical equipment sales. Although it is anticipated that growth in sales of SDH/SONET will gradually decline in the next few years, the huge installed base of SONET/SDH equipment is not likely to be replaced in the foreseeable future. SDH is favored by network operators for its ability to offer resilient bandwidth and infrastructure scalability both nationally and internationally with proven Operation, Admin- istration, Management, and Provisioning (OAM&P) capabilities. The rise of the Internet and widespread adoption of Internet technologies deployed within corporate intranets has fueled the explosive growth of bursty IP traffic and subsequently the deployment of large IP/MPLS routers with large-capacity Wide Area Network (WAN) interfa