. There are both traditional-but-fast-advancing solutions and new-but-not-yet-large-scale- tested solutions. This book is part of a two-volume set on this topic. This book examines traditional-but-fast-advancing architectures and technolo- gies; the companion book3 examines the new-but-not-yet-large-scale-tested solutions, which promise to alter the landscape of the metro access/metro Advances and Opportunities in Next-Generation SONET core environment. There is virtually no overlap between the two books, except for the few introductory concepts in the following subsection. Currently, service providers, enterprise network planners, and technol- ogy developers are being forced to rethink transport, routing, switching, and traffic management for the networks now in the process of being planned and/or deployed. Changes in architectures and infrastructures for broad- band deployment could be far reaching. These implications are discussed in the material that follows. 1.1 Background Industry observers have called 2001 a watershed year in the telecommuni- cations and data communications industry. Five factors have relevance to a discourse on the new-generation networks that planners may consider deploying in the near future: (1) the recent passing away of many legacy narrowband service providers such as Competitive Local Exchange Carri- ers (CLECs), Digital Subscriber Line LECs (DLECs), Building LECs (BLECs), Radio LECs (RLECs), Ethernet LECs (ELECs), and Internet ser- vice providers (ISPs); (2) the need for cost-effective, but financially sound broadband service delivery; (3) the major recent advances in optical tech- nologies; (4) the apparent glut of fiber facilities in the long-haul portion of the network, but the absolute dearth of such facilities for the use of broad- band services in the local metro access/metro core segment of the network; and (5) the emergence of new access and backbone architectures, in partic- ular Ethernet-based WAN approaches. A sixth factor has also become per- tinent of late: the need to