NZDSF which can support OC-192 at 10 Gbits/s, the higher operating rate requires optical regenerators at approxi- mately every 40 km. Thus, although four fiber pairs could support the 40 Gbit/s rate obtained from DWDM, the number of regenerators would grow to 100. WDM and DWDM Developments In much the same way as the evolution of a 1908 baseball play was referred to as "Tinker to Evers to Chance," which referred to the key infield players on the Cubs, we can use the acronyms WDM to DWDM to UDWDM to denote the evolution of wavelength division multiplex- ing. During the late 1990s systems with 32 to 64 channels operating at OC-48 data transmission rates resulted in the ability of a single optical fiber to support a composite transmission rate between 32 X 2.5 Gbits/s or 80 Gbits/s and 64 X 2.5 Gbits/s or 160 Gbits/s. Because OC-48 operating rates permitted the use of a wide range of optical fiber, most WDM systems, which were soon referred to as DWDM, operated their individual wavelengths at 2.5 Gbits/s. However, by the new millennium, the low-dispersion fiber being installed by many relatively recently formed telecommunications companies permitted OC-192 at 10 Gbits/s to become a reality. In competition, well-established communications carriers added new optical fiber to their infrastructure, which enabled them to upgrade to OC-192. Although migration from OC-48 to OC-192 may appear to permit a composite increase by a factor of 4 in the data transmission rate capabil- Fiber in the WAN ity of a fiber, the actual gain is more complex. This is because in an OC- 48-based DWDM system signals are separated from one another by 0.4 nm (50 GHz), but in OC-192 signals are commonly allocated 0.8-nm slots. Thus, upgrading to an OC-192 DWDM system could result in a quadru- pling of the transmission rate on half the number of channels, resulting in a doubling of the composite rate carried by an optical fiber. However, before we put down our pencils, a few words about evolving systems are in order. Nortel has introduced an OC-19