which is large relative to the wavelength of the light passing through it; as a result, multimode fiber suffers from modal dispersion (i.e., the tendency of light to travel in a wave-like motion rather than in a straight line), and repeaters need to be spaced fairly close together (about 10 to 40 miles [16 to 64 km] apart). The diameter of multimode fiber also has a benefit: It makes the fiber more tolerant of errors related to fitting the fiber to transmitter or receiver attachments, so termina- tion of multimode is rather easy. The more high-performance mode of fiber, single-mode fiber, has a fiber diam- eter that is almost the same as the wavelength of light passing through it-from 8 microns to 12 microns. Therefore, the light can use only one path: It must travel straight down the center of the fiber. As a result, single-mode fiber does not suffer from modal dispersion, and it maintains very good signal quality over longer dis- tances. Therefore, with single-mode fiber, repeaters can be spaced farther apart (as mentioned earlier, they are currently about 500 miles [804 km] apart, with the dis- tances increasing rapidly). But because single-mode fiber has such a small diame- ter, it is difficult to terminate, SO experienced technical support may be needed to perform splices and other work with single-mode fiber. The bottom line is that multimode fiber is less expensive than single-mode fiber but offers lower performance than single-mode fiber. Single-mode fiber is more expensive and offers higher performance, and it has been used in most of the long-distance networks that use fiber. Light Sources In the realm of light sources, there are also two categories: light-emitting diodes (LEDs) and laser diodes. The cheaper, lower-performer category is LEDs. LEDs are relatively inexpensive, they have a long life, and they are rather tolerant of extreme temperatures. However, they couple only about 3% of light into the fiber, so their data rates are low, currently about 500Mbps. Laser diodes are capable of much higher t