e right-sized SONET connections. Such technology enables new services such as user-based subscription and bandwidth on demand.¹ Although bandwidth efficiency is important, we have noted several times in this book that transport bandwidth efficiency is not the linchpin that will make or break the deployment of broadband to the enterprise level. Enterprise locations primarily need affordable, timely, reliable, broadband connectiv- ity; efficiency of the payload is just an element of the overall desiderata. ATM was the multiplexing (read-efficient payload) par excellence. Once the cell tax was paid, near-perfect packing of any bursty stream can be achieved, typically with overall overbooking ratios of 5 or 10 (which more than compensate for the 20 percent or so of tax overhead). Yet ATM did not see major deployment just on the basis of bandwidth efficiency and QoS. 11 The main reason was the operational cost for both the user and the carrier; both the user and the carrier had to deploy completely new equipment and establish new procedures (at both ends) for fault management, capacity management, accounting management, performance management, and security management. The overall operational cost proved to be too high in spite of the major bandwidth efficiency achieved with overbooking ratios of 5 to 10 times. Next-Generation SONET and Optical Architectures 4.5 Implementation Example As noted previously, next-generation SONET products take one of three forms, as shown in Table 4-3. In this section, we look at one possible implementation philosophy for a hybrid solution. The following list briefly describes an example of a next- generation SONET product family (from the Nortel Networks application brief, "Optical Internet Cable Solutions") and Figure 4-11 describes topo- logical deployment. Nortel OPTera Metro 3100 Compact for small business, this offers an OC-3 line rate with available tributaries, including 8 DS1s plus 12 DS1s, 1 DS3/EC1, or 1 OC-3/3c. Figure 4-11 Typical topological Optical Metro Backbone deployment