A communication line composed of a cable core made up of multiple insulated wires or conductors, encased in a sealed sheath. Some have an additional outer layer outside the sheath. There are various laying methods, including overhead, direct burial, pipeline, and underwater. Structurally, they are categorized as symmetrical, coaxial, and composite cables; functionally, they are field and permanent cables (underground and submarine cables). Communication cables have a wide transmission bandwidth, large communication capacity, minimal external interference, but are difficult to maintain. They can transmit telephone, telegraph, data, and images, etc.
