Use the calculations described in this section to determine the actual maximum for your network. If the distance between two connected stations exceeds this limit, transmission can become unreliable. Proper operation of an optical data link depends on modulated light reaching the receiver with enough power to be demodulated. If the power margin is zero or positive, the link should work. If it is negative, the signal may not arrive with enough power to operate the receiver.
Attenuation is significantly lower for optical fiber than for other media.
In multimode fiber, the signal spreads in time because of the different propagation modes. The power lost over the data link is the sum of all these losses. Table 12-6 gives an estimate of the amount of loss attributable to each cause. 1 dB 1 Dispersion is usually negligible for single-mode fiber. For multimode fiber, the product of bandwidth and distance should be less than 500 MHz-km.