Network switches make the connection between one phone and another.
Several switches are often involved in a single telephone conversation. Until the mid-1960s, the switches were electromechanical relays. About 30 years ago, Bell Labs began introducing computerized switches that were faster, cheaper, small, more energy-efficient, and far more sophisticated. Long-distance calls usually go through several network switches, which may have been manufactured by several different vendors, which may have different responses to 2000 as a year date. PBX systems are used in most medium to large-sized companies and government agencies.