The fastest way to transmit information between continents is through undersea fiber-optic cables. Some of these cables can transmit the equivalent of 62,500 written pages per second. About the diameter of a golf ball, they consist of optical fibers (usually made of glass) that are reinforced and protected by steel wires and a waterproof coating. Because they rest on the ocean floor, cables must be installed and repaired by special ships (cable ships). Undersea cables were originally used primarily for telephone connections to transmit voices from continent to continent. In some areas of the world today, Internet traffic volume is twice that of voice.