e adaptive nature of this approach, which is man- aged at the physical layer, circumvents the need for complex traffic engi- neering on access rings. According to these same proponents, the service provider's SONET access rings leveraging this mechanism can be consid- ered future-proofed against new and unforeseen application traffic that may adversely impact network loading. Finally, this real-time approach to virtual concatenation not only achieves new levels of efficiency in access- Allocated STS-1 Figure 4-14 Regular DBA approach. STS-1 DBA Pool OC-48 Next-Generation SONET and Optical Architectures ring utilization, but it also enables new services such as usage-based billing. In the past, a multiservice operator had only two choices for metro delivery and transport: using an overlayed, routed IP network or mapping Ethernet into SONET frames. Because the first solution is built for data and there- fore not optimized for multiservice, we must analyze the second SONET solution. With each 10-Mbps LAN service requiring an STS-1 bandwidth, an OC-48 (2.5 Gbps) metro ring has the capacity to carry 48 individual LAN circuits with approximately 1.9 Gbps of stranded bandwidth. This is not very efficient and it is one of the major reasons why incumbent service providers are not able to offer cost-effective LAN service over existing SONET networks. Virtual concatenation would enable the service provider to offer significantly more 10-Mbps LAN circuits. Given that a OC-48 metro ring has 1,344 VT1.5s, with each 10-Mbps circuit requiring 7 VT1.5s, the service providers can now deliver 192 LAN circuits in the same amount of bandwidth-an increase of more than 300 percent. It must be further understood that because each circuit is rarely operating anywhere near 10 Mbps, DBA can also be implemented. It is conceivable that an oversub- scription of 4 could be engineered, meaning at any given time, 4 users could share an equivalent 10 Mbps of bandwidth. This results in an additional 576 10-Mbps LAN services, bringing the total to 