Optical fiber is a hair-thin strand of glass, specially designed to trap and transmit light pulses. The fiber uses light instead of electricity to carry a signal. It is unique because it can carry high bandwidth signals over long distances without signal degradation, and it can provide those signals simultaneously in both directions – upload and download. Copper media can also carry high bandwidth, but only for a few hundred yards – after which the signal begins to degrade and bandwidth narrows. Optical fiber has been used in communications networks for more than 35 years, mostly to carry core telecom traffic from city to city or country to country.