interfaces in order to meet a wide range of end-user requirements. Occa- sionally, user information rates may need to be assigned in increments of 10 Mbps for flexible service level agreements (SLAs) and additional scalability. However, as bandwidth becomes a commodity, the precise (perhaps rationed) amount of bandwidth on a link becomes less of a differentiating factor for various providers. Value-added solutions will be of increased interest to the end user compared to just pure bandwidth solutions. Frankly, there is relatively little incentive for a provider that has just Chapter 4 incurred a nontrivial expense bringing a building online to fine-tune the billing in order to distinguish, for example, between a customer's needs requiring 58 Mbps today, 59 Mbps tomorrow, and 57 Mbps the day after tomorrow. It appears at the practitioner's level that customers are more likely to be interested in 10 Mbps on a 10-Mbps interface; 50 Mbps or 100 Mbps on a 100-Mbps interface; and 50 Mbps, 100 Mbps, 200 Mbps, 500 Mbps, or 1,000 Mbps on a 1,000-Mbps interface. The fine-grain 1-Mbps granularity that some equipment vendors are bringing out appears to have rather limited commercial value. After all, if bandwidth is expected to be SO abundant in the future, why be so precise about the amount of the com- modity delivered? Next-generation SONET technologies leverage virtual concatenation in order to right-size the bandwidth of the data-centric connection. We dis- cussed in Chapter 2, "Optics Primer," the existence of a mechanism (VT) to map DS1 and DS2 signals onto the SONET payload in an efficient manner. Some people argue that there is a further need to define VTs that are data oriented-for example, 10 and 100 Mbps (and combinations thereof). For example, a 10Base-T interface could be mapped to 7 SONET VT1.5s, resulting in an increase of approximately 95 percent in transport effi- ciency. Vendors leveraging virtual concatenation typically provide a soft- ware-based approach to the creation, deletion, and modification of thes