city is expanded several dozen times. It should be noted immediately, however, that the cost of DWDM gear is not trivial (it could be $120,000 or more per node, with the cost being a function of the number of wavelengths supported). Therefore, although it is easily justifiable at the long-haul level, it remains a design cost issue for metro access networks and to some extent for metro core networks as well. Second-generation equipment spanned the 1995 to 2000 time frame. Figure 3-2 Second-Generation Optical Network Second-generation optical network. SONET switch SONET Dense Wave Division Multiplexing System SONET Amplifier switch SONET Chapter 3 Typically, for each DWDM channel added, a SONET device needs to be stacked in front of the DWDM terminal to provide the wavelength source. Also, the additional capacity drives a proliferation of DXCs as more elec- tronic traffic needs to be routed and groomed. Because of cost, the ideal application for this technology is long haul. The second generation has been described as "pushing SONET to the edge of the network." This refers to the fact that SONET is no longer connected directly to the fiber ring itself, but is connected to the DWDM terminal instead. This idea of pushing SONET to the edge of the network has further implications for the third generation of optical networking, which is described next. 3.1.3 Third-Generation Optical Networks The third generation of optical networking has evolved to deal with the cost/performance issues associated with SONET and digital crossconnect system (DCS) deployments in second-generation systems. Third-generation equipment also brought a greater level of sophistication to optical net- working. Third-generation equipment spans the 2000+ time frame. At a high level, this equipment Incorporates the SONET, DWDM, and crossconnect functions into a fewer number of discrete, cost-reduced devices. Adds more intelligence to optical networking, specifically by enabling routing/switching at the wavelength level. (This is also often referred t