Figure 3-20 Switching Node Switching Node Typical metro-level network. SONET SONET Switching Node Survivable Switching OAM&P Switching Node Survivable Mid-Span Switching Figure 3-21 Expansion of SONET to a greater Add/Drop metropolitan area. Add/Drop Hub Topology in Suburban and Rural Areas Mesh Topology in Metropolitan Core for Potential Restoration Routes Traditional SONET Architectures Figure 3-22 Regional or national SONET network. SONET Terminal SONET Hub SONET Add/Drop Mux used in Repeater Configuration 3.2.7 Synchronous Digital Hierarchy (SDH) Outside of North America, carriers adhere to SDH standards. 11 TDM sys- tems in North America combine 24 DSOs into one 1.54-Mbps DS1 signal. European TDM multiplexes 32 E0s into one 2.048-Mbps E1 signal. (The European standard has become common in many parts of the world.) Table 3-1 compares the North American and European traditional transmission hierarchies. The original goal of the standardization effort was to efficiently accommodate both the 1.5- and 2-Mbps nonsynchronous hierarchies in a single synchronization standard. The agreement that was eventually Chapter 3 Digital Figure 3-23 Point-to-point use of Users Carrier SONET for traditional Switching Node services and SONET SONET ring/mesh use for Swich Switch Terminal new services (such as Interface or SONET transparent LAN Cross- service [TLS]). connect Consolidation of Services at Hub DS3 or DS1 Customer Premises T1 Mux DS3 or DS1 Special Services DS3/OC-3c/OC-12c Router Device Ethernet DS3/OC-3c/OC-12c Router Table 3-1 North American Rate European Rate Comparison of Signal Speed Channels Signal Speed Channels DSx/Ex Hierarchy 64 Kbps 1 DSO 64 Kbps 1.54 Mbps 24 DSOs 2.048 Mbps 32 E0s 6.3 Mbps 96 DSOs 8.45 Mbps 128 E0s 44.8 Mbps 28 DS1s 34 Mbps 16 E1s Not defined 140 Mbps 64 E1s Traditional SONET Architectures Table 3-2 SONET Bit Rate SONET/SDH Convergence STS-1/OC-1 51.84 Mbps STS-3/OC-3 155.52 Mbps STM-1 STS-12/OC-12 622.08 Mbps STM-4 STS-24/OC-24 1,244.16 Mbps STS-48/OC-48 2,488.32 Mbps STM-16 STS-192/OC-19