It appears as bursts at the receiver, and when present can have a catastrophic effect due to its large power. When radio links are used, interference from other transmitters can be problematic. Thermal noise is always present. It is due to the random motion of electric charges present in all media. It can be generated externally, or internally at the receiver.
Equation says that hot systems generate more noise.
A bit error in a transmitted signal due to channel effects Communications channels can be a physical connection between correspondents. Wires, coaxial cables and optical fibres are used for this purpose. Roughly speaking, the bandwidth and expense increases along this list. When distances, or the cost of cable laying become very large, it can be advantageous to use radio waves as the channel. Radio and television broadcasting is the natural method for communicating unselectively with large numbers of correspondents, or when one or both of the correspondents are moving.