 fibers in the cable. The meaning of the S field is discussed next. S defines the mode of the fiber and wavelength at which the attenuation is specified, as shown in Table 2-3. Character S2 defines the transmission performance of the cable. S2, in conjunction with S1,7 indicates the maximum attenuation or the minimum bandwidth (in MHzXkm) of several different fibers, as indicated in Table 2-4. The objective for the average attenuation coefficient of all fibers in a cable should be no greater than 80 percent of the maximum coefficient given in the table. Table 2-2 Application Wavelength Distance Distances Sup- ported by Multi- 10-Mbps Ethernet, 10Base-FL 850-nm MM 2,000 m mode Fiber 100-Mbps Fast Ethernet, 100Base-FX 1,310-nm MM 2,000 m 100-Mbps Fast Ethernet, 100Base-SX 850-nm MM 300 m GbE, 1000Base-SX 850-nm MM 220 m/550 m* GbE, 1000Base-LX 1,310-nm SM 550 m *62.5um/50um fiber Chapter 2 Table 2-3 Usable Wavelengths (um) Fiber Mode and 0.85 and 1.30 and Attenuation Fiber Type Wavelength Defined by S Single mode 2 or 3 Dispersion shifted 50/125 multimode 62.5/125 multimode 85/125 multimode Power P = iV = i°R = V2/R Decibel This standard unit is used to express transmission gain or loss, and relative power level. One decibel (dB) is 1/10 of a bel. It is used to describe the ratio of the power at any point in the transmission line to a reference of 1 milliwatt of input. (The ratio expresses decibels above or below this reference level of 1 milliwatt.) DBM is used when a power of 1 milliwatt is the reference level. dB indicates the ratio of power output to power input: dB = 10 log10 (P/P) (Transmission) System Power In Power Out Optics Primer Table 2-4 Character S2 for Conventional Single-Mode Fiber Character S2 Character 1.30 um Attenuation (dB/km) Character S2 for DSF Character 1.30 um Attenuation (dB/km) Character S2 for DSF Character 1.55 um Attenuation (dB/km) Character S2 for Multimode Fiber, 50/125 Minimum Maximum Attenuation (dB/km) Bandwidth (MHzxkm) 0.85 um 1.30 um 1,000 1,200 1,500 Character S2 for 62.5/12