In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. Transmission lines carry electric energy from one point to another in an electric power system, and they can carry alternating current or direct current. They are used for purposes such as connecting radio transmitters and receivers with their antennas, distributing cable television signals, routing calls between telephone switching centers, computer network connections, and high-speed computer data buses. The transmission line is modeled with a resistance (R) and inductance (L) in series with a capacitance (C) and conductance (G) in parallel. The resistance and conductance contribute to the loss in a transmission line. Electrical transmission lines are widely used to transmit high-frequency signals over long or short distances with minimum power loss. A transmission line is considered an interconnect when its length is at least one-fourth of the signal wavelength. The behavior of RF interconnects is very different from that of ordinary wires carrying low-frequency signals, so additional terminology is used. PCB traces also function as transmission lines, and their characteristics are controlled directly by the designer. The electric system involves generation, transmission, and distribution, and the need for bulk transmission came about as demand for electricity grew and small power plants that could only serve their local area became inadequate. Transmission lines were the only way to get the power to where it was needed.