t. DWDM increases the capacity of the embedded optical fiber base by adding pair- gain methods to the transmission channel. A DWDM optical backbone gives carriers the flexibility to expand capacity in any portion of their network, thus addressing specific problem areas that are congested due to high band- width demands. However, any network planner knows that as you move closer to the core, the need becomes more intensive and concentrated, whereas at the edges of the network, the need is less intensive and concen- trated. Therefore, the long-haul core is a more natural habitat for DWDM technology than the metro access and metro core space. In long-haul networks, the primary value provided by DWDM in com- bination with OLAs is the cost-effective transmission of high-aggregate bit rates over large distances on a single fiber pair. The large distances in long-haul networks make deploying new fiber challenging. Long-haul carriers have traditionally been the first to embrace advances in trans- mission technologies to gain additional capacity while leveraging their existing equipment.13 The versatile nature of DWDM technology enables Asynchronous Trans- fer Mode (ATM), Internet Protocol (IP), and SONET networks to share the same optical core (see Figure 5-12), but possibly with some bandwidth inef- ficiencies. (For example, yes, you can map a GbE link directly over a lambda, but you will be dedicating a channel to support 1 Gbps where you could otherwise derive 2.5 Gbps/OC-48 or 10 Gbps/OC-192.) DWDM pro- vides a means for carriers to integrate diverse technologies of their existing networks onto one physical infrastructure. DWDM systems are bit-rate and format independent and can accept any combination of interface rates and formats, although SONET tributaries are the most common. DWDM pro- vides a grow-as-you-go infrastructure that allows for a 10- to 100-fold capacity expansion as new services increase demand for bandwidth. The grow-as-you-go approach is implemented by adding the lambda plug-ins Dense Wavelength Div