In the early years of telecommunications, the only way of linking one telephone with another was by fixed cables. Links between continents relied on cables under the sea. These cables had to be strong enough to resist attack by salt water, ocean currents and water pressure, so had a thick, water resistant cover made of steel. Inside were the copper wires that carried the power and signal. These have now been replaced by the fiber optic cables which have the capacity to transmit messages at a faster rate. Satellites have now changed every thing. They sit at an exact height above the earth’s equator and they rotate at the same speed as the Earth spins. Telephone signals can be sent to the satellites and bounced back to Earth. Every where on the planet can be covered by only five or six satellites, except for the poles and surrounding areas, which are out of their range.