nsparency, end- user protocol support, speed of provisioning, and end-to-end connectivity. During the 1990s, the metro network was primarily concerned with the transport of voice-based TDM circuits (DS1 and DS3) for private-line ser- vices. Recently, the issues related to the metro network are how to support the emergence of data services based on IP and lambdas, as well as how to support the continued growth of legacy TDM. Another related issue is how to build the metro network to support the shift from legacy TDM to a data- centric network based on IP. Metro access and core networks have to carry many different types of traffic over an optical channel, regardless of the protocol (Ethernet, ATM, SONET, and so on) or bit rate (10 Mbps, 2.5 Gbps, and so on). Figure 5-31 Dense Wavelength Division Multiplexing (DWDM) Systems 100 Mbps Ethernet, Figure 5-31 Gigabit Ethernet, Metro DWDM Multitenant Office Tower ATM, SONET, etc. Carrier Central Office applications example. Carrier Other Service Devices Customer- Building Network Interface Interoffice Access Ring Network Devices Other Building typifies an access network with protocol and bit-rate independence. Native data interfaces, such as Ethernet at various speeds, can be connected directly to the transport platform without additional adaptation. As we dis- cussed in the Chapter 4, "Next-Generation SONET and Optical Architec- tures," next-generation SONET targets precisely this segment. For Figure 5-31 to be more than just a picture, the cost per building for the DWDM needs to be $10,000 to $20,000 for GbE and 10 GbE applications and $5,000 to $10,000 for 10-Mbps and 100-Mbps transparent LAN service (TLS). Nearly all enterprise data traffic now originates in Ethernet format (10 Mbps/100 Mbps/GbE), while the backbone is built on optical rates of 2.5 and 10 Gbps with STS-1 granularity. This is why it is important for metro WDM devices to support the data-oriented interfaces; this would not be a requirement for long-haul DWDM. On the other hand, a tradi- tional (telco) 