down a number of different pathways. Optical switching will become the foundation for building these types of integrated networks (see Figure 11.2). Network Reality Today Today's network reality involves a complex layering of many different architectures and their individual control planes. As shown in Figure 11.3, today's network has SDH/SONET Rings Long Distance SONET multiplexer Regional OC-192 (10Gbps) Data (DSL Local OC-48 or cable) OC-12 (2.5Gbps) (622Mbps) (T-1/E-1/J-1) Voice Figure 11.1 An example of today's optical networks Chapter 11 Optical Networking Optical Switch Voice and Data Figure 11.2 An example of tomorrow's optical networks Routing Network IP Transport Switching ATM, Frame Relay, Ethernet Restoration SDH/SONET Rings, ADMs, Digital Cross-Connects Bandwidth Point-to-Point, DWDM, Optical Links Figure 11.3 Network infrastructure today many layers of packet data networks-including IP, Frame Relay, ATM, and MPLS- all operating over mesh topologies. These packet networks sit on top of SDH/ SONET rings. The rings themselves are stacked, addressing the specific require- ments of access networks, metro networks, or core networks. They facilitate fast restoration in the event of failure, but adding capacity is an intensive manual pro- cess. The SDH/SONET rings further sit on top of DWDM networks, which are point-to-point systems that involve link-by-link management and massive traffic connections at the tandem offices. The management and traffic problems will get worse as systems grow in capacity. Today's systems carry 160 wavelengths or more, and at 10Gbps per wavelength, a 160-wavelength system offers 1.6Tbps of traffic; Optical Networking Today and Tomorrow the capacities-that is, the number of wavelengths and bits per second per wave- length-are increasing every year. Multiple packet data networks run over SDH/SONET, which runs DWDM. Packet networks are naturally resilient. Therefore, the cost of overbuild- ing SDH/SONET may not be justified. Some services still expect 50-millisecond restoration, bu