lse broadening or compression (depending on the dispersion profile of the fiber). This issue is also being studied with the goal of finding workable solutions. Four-wave mixing Limits multichannel transmission on DSF that has its zero dispersion in the EDFA bandwidth range. Monitoring input power levels into the EDFA can address this problem when conventional fiber is used for transmission. New fiber designs, including NZDSF, have been introduced to address the issue. The majority of embedded fiber in long-haul networks is standard, single-mode (G.562-defined) fiber with dispersion in the 1,550-nm window, which limits the distance for OC-192 transmission. The majority of the legacy fiber plant cannot support high-bit-rate TDM. Vintage fiber has some attributes that lead to significant dispersion and would therefore be incompatible with high-bit-rate TDM. State-of-the-art OC-192 SONET technology is a viable alternative for new fiber builds because the fiber parameters can be controlled through the placement of the appropriate fiber type and because new fiber-handling procedures can be accommodated. However, for existing fiber applications, the capability to install 10-Gbps TDM systems depends on fiber properties such as chromatic dispersion and PMD, which may differ from fiber span to fiber span. In addition, high-rate TDM systems require specialized fiber- handling and termination procedures when compared to lower-rate OC-48 systems. In contrast, current DWDM systems can transport up to 32 wave- lengths at OC-48 each, giving an aggregate capacity of 80 Gbps on one fiber pair. This means WDM technology surpasses TDM in terms of the aggre- gate capacity offered on a fiber pair while maintaining the same fiber- handling procedures developed for OC-48 TDM systems.13 13 SONET and WDM systems typically have built-in forward error correction (FEC) fea- tures that provide a 10-15 bit error rate (BER). Figure 5-25 depicts an exam- ple of typical interfaces supported by an OC-192 NE. DWDM has a number of advantages over ev