The telecommunications network was a system of interconnected facilities designed to carry traffic that results from a variety of telecommunications services. When viewed from the perspective of its physical components, or facilities, the network may be referred to as the facilities network. The components of the facilities network may be divided into three broad categories.

Station equipment is generally located on the customer’s premises. Its primary functions are to transmit and receive the information flow and required control signals between customers and the network.

Transmission facilities provide the communications paths that carry the information between customers. In general, transmission facilities consist of some sort of transmission medium (for example, the atmosphere, paired cable, coaxial cable, lightguide cable) and various types of electronic equipment located at different points along the transmission medium. This equipment amplifies and, sometimes, regenerates the transmitted signals. In addition, various types of facility terminal equipment provide functions needed where transmission facilities connect to switching systems and at facility junction points.

Switching Systems interconnect the transmission facilities at various key locations and route traffic through the network. The introduction of central switching into the network yields cost savings in station equipment and transmission facilities.

In addition to the functions just described, transmission facilities and switching systems provide for signaling in the network. The Bell System provides a large percentage of the telecommunications facilities in the United States nationwide network. However, numerous independent telephone companies and other common carriers also own both transmission facilities and switching systems.