s at no more than $20,000 to have any chance of being profitable. Furthermore, the high building cost is multiplicative-every building in the ring would require the expensive optics. Although high-cost DWDM might be acceptable for point- to-point applications (not rings with 8, 16, or 32 buildings on them) and for long haul, it is completely unacceptable in the metro space. Observers cite the following drivers for the introduction of new metro optical architectures and technologies: End-user drivers/issues Increased capacity demand at the access level Demand for lower-cost, higher-reliability, and diversified facilities Fiber-based services available in more locations Decreased competition (fewer providers around) Service provider factors Need for decreased capex and opex, and requirement for improved bottom line Revenue opportunities in optical layer Network simplification and equipment consolidation Mesh network efficiency and flexibility New optical-networking technologies continually entering the market Shorter end-user service contracts, which implies the need for faster depreciation Table 1-1 depicts the typical end-user applications in terms of a number of key service parameters. The various metro architectures need to support Advances and Opportunities in Next-Generation SONET Table 1-1 Voice Video Typical End-User Applications Capacity Narrowband/ Narrowband Broadband traditional apps Broadband/new apps Bursty Tolerance for delay Medium or jitter Quality of service For some Deterministic Deterministic (QoS) applications always always Restoration Medium Medium requirements Fault tolerance Medium Low/medium some or possibly all of these requirements. Broadband user-level applica- tions include intranet data networking, storage and backup site connectiv- ity, high-speed Internet access, and multimedia applications (see Figure 1-4 for examples). In spite of recent advances in optical technologies, an intrinsic need to disruptively increase the available metro/WAN throughput remains. A trend is developing in 