than the light that escapes into and trav- els in the cladding. This results in a dispersion effect that can be cor- rected by transmitting at specific wavelengths where material and waveguide dispersion actually occur at minimums. Putting It All Together So what does all of this have to do with the high-speed transmission of voice, video, and data? A lot, as it turns out. Understanding where atten- uation and dispersion problems occur helps optical design engineers determine the best wavelengths at which to transmit information, taking into account distance, type of fiber, and other factors that can potentially affect the integrity of the transmitted signal. Consider the graph shown in Figure 7-21. It depicts the optical transmission domain, as well as the areas where problems arise. Attenuation (dB/km) is shown on the Y-axis; Wavelength (nm) is shown on the X-axis. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Transport Technologies Figure 7-21 OH Absorption Peak First Second The optical Window Window transmission Total domain Rayleigh Scattering Wavelength (nm) First of all, note that there are four transmission windows in the dia- gram. The first one is at approximately 850 nm, the second at 1,310 nm, the third at 1,550 nm, and the fourth at 1,625 nm; the last two are labeled "C" and "L" band, respectively. The 850 nm band was the first to be used because of its adherence to the wavelength at which the original LED technology operated. The second window at 1,310 nm enjoys low dispersion; this is where dispersion effects are minimized. At 1,550 nm, the so-called C-Band, emerges as the ideal wavelength at which to oper- ate long-haul systems and systems upon which dense wavelength divi- sion multiplexing (DWDM) has been deployed because (1) loss is minimized in this region, and (2) dispersion minimums can be shifte