ew of Wireless Personal Com- munications," IEEE Communications Magazine, Jan. 1995. 19. R. L. Freeman, "Telecommunication System Engineering,' 4th ed, Wiley, Hoboken, NJ, 2004. ADVANCED BROADBAND DIGITAL TRANSPORT FORMATS 19.1 OBJECTIVE AND SCOPE In the early 1980s, fiber-optic transmission links burst upon the telecommunication trans- port scene. The potential bit rate capacity of these new systems was SO great that there was no underlying digital format to accommodate such transmission rates. The maximum bit rate in the DS1 family of digital formats was DS4 at 274 Mbps; and for the E1 family, E4 at 139 Mbps. These data rates satisfied the requirements of the metallic transmission plant, but the evolving fiber-optic plant had the promise of much greater capacity, in the multigigabit region. In the mid-1980s ANSI and Bellcore began to develop a new digital format standard specifically designed for the potential bit rates of fiber optics. The name of this structure is SONET, standing for Synchronous Optical Network. As the development of SONET was proceeding, CEPT¹ showed interest in the devel- opment of a European standard. In 1986 CCITT stepped in proposing a singular standard that would accommodate U.S., European, and Japanese hierarchies. This unfortunately was not achieved due more to time constraints on the part of U.S. interests. As a result, there are two digital format standards: SONET and the synchronous digital hierarchy (SDH) espoused by CCITT. It should be pointed out that these formats are optimized for voice operation with 125-usec frames. Both types commonly carry plesiochronous digital hierarchy (PDH) formats such as DS1 and E1, as well as ATM cells.2 In the general scheme of things, the interface from one to the other will take place at North American gateways. In other words, international trunks are SDH-equipped, not SONET-equipped. The objective of this chapter is to provide a brief overview of both SONET and SDH standards. 1 CEPT stands for Conference European Post & Telegraph, a European tel