(LTE) (LTE) (PTE) (PTE) (PTE) (PTE) (PTE) Local Network-Based Local Clock Stratum Clock Clock if correct, this analysis would drive the SONET metro market to flatten and, in a few short years, disappear completely. But that hasn't happened. Analysts are forecasting that the SONET metro market will grow from around $5 billion in 2001 to more than $9 billion by 2003. However, there is one major caveat: According to proponents, the SONET equipment of the early to mid-1990s is nothing like the next generation of sophisticated, mul- tiservice, metropolitan optical nodes that will dominate this space in the coming years. 33 SONET/SDH metro access architectures favor a collection of two node rings instead of multinode rings, as illustrated in Figure 1-18.35 SONET/ SDH rings are utilized because of the high-speed restoration in case of a fiber cut or other link anomalies. Two node rings are often used at the metro core level between POPs because of the capability to support maintenance on transmission systems without affecting more than one site. (Multinode rings are typically not used in local environments because any upgrade that is done to one access site requires an upgrade to all of the systems on the ring, instead of only the site that needs it.) SONET/SDH multinode rings are more often used in long-haul backbone transport infrastructure. Multinode rings cost more than mesh networks, but they provide faster restoration where traffic restoration over distances is more of an issue. For a typical regional architecture, see Figure 1-19. This topic will be treated at length in Chapter 3. Advances and Opportunities in Next-Generation SONET Figure 1-18 OC-12/48 Metro Typical SONET/SDH Access Rings local architecture. SONET Ring Metro POP & CO Sites Standard Circuits Provisioned over Metro Transmission Network Metro Backbone SONET Rings SONET Ring On-Fiber Customer Building Sites 1.4.2 DWDM Positioning DWDM systems are used to carry multiple signals on a single fiber simul- taneously. More than 16 million lambda miles of D