ision Multiplexing (DWDM) Systems Figure 5-12 SONET/SDH Service Terminating SONET versus SONET/SDH Network Element (OC-48/192/ optical plane. Layer STM-16/64) SONET/SDH Regenerator (OC-48/192/STM-16/64) Fiber DWDM Termination Site Fiber Fiber Optical Layer Fiber Optical Amplifier Optical Add/Drop Site over time. 14 High-end commercially available DWDMs can deliver up to 320 Gbps of capacity; these are 32-channel systems with each channel operat- ing at 10 Gbps (OC-192). Optical technology under development at the com- mercial level can currently provide 10 Gbps on a single lambda and 160 lambdas over a single fiber pair for long-distance networking services (more lambdas are achievable in laboratory systems). However, many observers now believe that there was an overestimation of the demand in the late 1990s and early 2000s, at least in the long-haul and Internet segments of the market, and that those very large systems will not be needed in the near future. 5.2.2 EDFA Role in DWDM In WDM, multiple wavelengths of light carry the data channels to an opti- cal multiplexer where they are combined for transport over a single fiber pair, as shown in Figure 5-13. Essential to WDM technology is the optical amplifier, particularly for long-haul applications because they usually don't have much applicability in the metro space (see Figure 5-14). Optical ampli- fiers maintain continuity by amplifying the multiple signals simultane- ously as they travel down the fiber. The initial amplifier technology has EDFA. Now new extended-band amplifiers are being studied and devel- oped. These amplifiers carry the signal to optical demultiplexers where they are split into the original channel. Semiconductor optical amplifiers have been proposed for use in optical crossconnects (OXCs) for wavelength con- version in the optical domain and the amplification of a large number of ports. Support technologies include optical components (mux/demux Chapter 5 OC-48/OC-192 Lambda 1 OC-48/OC-192 MC VA MC VA Multiplexer Figure 5-13 Multiplexer Ba