rriers to End-to-End Optical Networking expand the capacity of their long-haul pipes. The response was to deploy those point-to-point links with DWDM. This resolved the bandwidth problem, but it nothing to address the routing issues. WDM and DWDM currently lack the intelli- gence required to really deliver meshed network configurations, and thus we have a need for optical switches. The main benefit of DWDM in the core is that it reduces deployment costs by eliminating the need for expensive amplifiers. Current DWDM products can operate successfully over about 300 to 450 miles (480 to 725 km), and there are examples of successful transmission up to 4,000 miles (6,400 km) without signal boosting. As mentioned earlier in this chapter, the process of regenerating signals represents as much as half of the overall cost of an optical deployment. Therefore, developments in extending distances are very promising. In the quest for expanding the capacity of WDM systems, in addition to employing new generations of amplifiers, such as Raman amplifiers, another strat- egy is to pack channels together more closely. This applies primarily to long-haul systems. Current DWDM systems space channels at 50GHz, but tighter spacing is also possible, including 25GHz and 12.5GHz spacing. Tighter spacing requires pre- cise lasers and channel separators. A vital application for WDM is in metropolitan area networks (MANs). MANs are becoming saturated, and network expansion is costly: Pulling fiber along existing conduits costs about US$30,000 per mile. But traditional DWDM systems are not well suited to MANs. For one thing, they were designed to work well on point-to- point links, but MAN traffic must be dropped and added frequently. DWDM does not present the same cost justifications in the MAN as it does in the core. The great savings that can come with DWDM in the MAN are due to the reduc- tion in the need for expensive amplifiers because, by definition, a MAN spans a fairly short distance. You can spend US$20,000 to US$30,000 or more for