 7 through 12 Service Endpoint A Service Endpoint Z OC-48 1 through 24 25 through 48 OC-192 1 through 96 97 through 192 Up to STS-24 Up to STS-24 Figure 3-48 Working Bandwidth Working Bandwidth Two-fiber BLSR dual- traffic routing-an OC-48 application is shown. OC-48 Two-Fiber BLSR Node Up to STS-48 Traffic-Termination Capacity Service Delivery via a Two-Fiber BLSR A service path is provisioned on a two-fiber BLSR by selecting endpoint network elements, tributary ports, and an STS-1 time slot linking the service entry and exit points. A service may reach its destination by traveling in either direction around the ring, as needed for optimum utilization of the available STS-1 channels. Intermediate nodes on the service path, if any, simply pass the service from east to west without modifying the STS-1 channel assignment. Chapter 3 The two-fiber BLSR architecture enables STS-1 channels to be reused as traffic is terminated at various locations around the ring-a feature that makes the architecture ideally suited for the distributed mesh and node-to- adjacent-node traffic patterns of interoffice networks. Reusable bandwidth also offers important synergies in ATM networks. Figure 3-49 illustrates how bandwidth can be reused on a two-fiber BLSR through application of STS-1 time slot assignment (TSA) technology. Note that Service A-B is routed from Node A to Node B around the east side of the ring using STS-1 channel 1. Because Service A-B terminates at Node B, STS-1 time slot 1 can be reused to transport Service B-C. The same chan- nel is reused again at Node C to transport Service A-D-C. Node D passes Service A-D-C through to Node A without modifying its time slot assign- ment. Thus, the sample two-fiber BLSR depicted in the figure is able to STS-1 Time Slot 1 Terminating Traffic STS-1 Time Slot 1 Figure 3-49 Service A-D-C Service A-B Reusing bandwidth in a two-fiber BLSR. Node A Two-Fiber BLSR Node OC-12/48/192 Bidirectional OC-12/48/192 Fiber Pair Bidirectional Fiber Pair Service A-B Node D Terminating Pass-Through 