ADM (switched lambdas). Naturally, there is also keen interest in reducing ser- vice provisioning time, if possible. In addition to technological changes, observers also anticipate architec- tural changes. The architecture of evolving optical networks could increas- ingly be based on mesh configurations rather than cascaded rings. Figure 7-3 depicts a hypothetical transition to a mesh architecture from a ring- based baseline. Keep in mind that the architecture shown on the right is more characteristic of a carrier's physical infrastructure than a user's over- lay logic in the United States, where a low-competition scenario means that only a handful of megacarriers provide the end-to-end set of services. The architecture is nearly perfect for the needs of these supercarriers. It is rem- iniscent of the predivestiture environment or perhaps of the Postal, Tele- graph, and Telephone (PTT) model of "one carrier has it all." The more complex architecture shown at the bottom left of Figure 7-3 is in reality more amenable to and representative of a multicarrier, multiplatform, mul- tispace, and multipurpose competitive environment. Mesh networks are often implied by simplified diagrams from equipment vendors and consul- tants to have abstract appeal, but such presentations fail to take into account the economic and business realities of networking in the United States. Assuming a best-in-breed stance, we can agree that a mesh network is generally more suited to long-haul networks, whereas a cascaded set of rings hanging off this mesh is more suited for metro applications. See Fig- ure 7-4 for an elaboration of this viewpoint. SONET Ring 2 SONET SONET Ring 3 Ring 1 SAN JOSE BOSTON Simple Cascade of Rings Long-haul National Metro Regional Regional Metro Metro Access Metro Access SAN JOSE BOSTON X = OXC A = ADM Meshed Network BOSTON SAN JOSE National Cascade of Rings Figure 7-3 Potential transition to meshed networks. All-Optical Networks Long-haul Figure 7-4 Metro Metro Metro Metro Hybrid architectures Access Access for t