 be mapped into traditional leased- or private-line circuits, these solutions are often costly and ineffi- cient from both the carrier and customer's point of view. Poor bandwidth utilization, lack of scalability, large numbers of hard-to-manage dedicated connections in mesh networks, and limited end-to-end management strate- gies are just a few of the many drawbacks. With these hybrid systems, transport bandwidth is provisionable from 50 Mbps up to 10 Gbps, enabling a carrier to add more users or increase sub- scriber bandwidth without reengineering the network. Traffic from differ- ent locations or customers along the ring is statistically multiplexed onto a shared pool of transport bandwidth, thus achieving bandwidth usage effi- ciency. These systems are pre-RPR (IEEE 802.17) technologies, but incor- porate many of the principles and ideas of the RPR philosophy. To ensure service continuity in the event of a network fault, Layer 2 automatic pro- tection switching (APS) reroutes traffic, typically in about 50 ms. A self- healing ring architecture provides the geographic diversity needed to ensure the survivability of critical data services. A connectionless packet data backbone ring with distributed Layer 2 switching inherently supports Next-Generation SONET and Optical Architectures the full/partial mesh traffic patterns typical of MAN/WAN applications. There is no need to provision and maintain large numbers of dedicated point-to-point connections on the backbone for mesh traffic. All fiber pairs and transport channels are available for data traffic without the require- ment to reserve capacity for protection (as in circuit-based transport appli- cations); this provides for backbone bandwidth doubling. A typical system may support an OC3/12 line rate with available tribu- taries including up to 84 DS1s, 4 DS3s/EC1s, 4 OC-3s/3cs, 8 100Base-T Eth- ernet, or mixed. Some of the benefits might include A 50 to 70 percent reduction in capital cost from present methods of operation due to the elimination of unnecessa