Panel Machine Switching System

The Panel Machine Switching System was a common control switching system developed by Western Electric. It was first introduced in semi-mechanical trial form in the Mulberry office in Newark, NJ on January 16, 1915. It was then installed and used by customers in Omaha, Nebraska in 1922. It went on to be installed in many major cities in the United States, serving 3.6 million lines by 1952.

Technical Summary

The panel system was fundamentally similar to the manual switchboard method of connecting telephone calls, only instead of using human operators to raise cords and plug them into jacks, it made use of power-driven selectors that hunted over tall banks of 500 terminals. The selectors were controlled by a sender, which mimicked the cognitive functions of the operator, such as recording the number the subscriber dialed, and "looking up" the correct path for a call to take through the network, and finally, driving the selector rods to their final position.

A panel switch usually consisted of a series of line finder frames, which served as a concentration point where subscribers could enter the switching network. Then, there were a series of selector frames: the District, Office, and Incoming frames. At the far end of the network were Final Selector frames, which also contained customer lines. A subscriber's telephone appeared twice in the panel system--once at a line finder frame for originating calls, and again at the final frame for calls terminating to that subscriber.

Terminology

Several new terms were devised during the development of the panel system.

• Power driven - Refers to the use of motor and clutch drive, as opposed to using relays and magnets to move the selectors, as in the Strowger and crossbar systems
• Full Mechanical - Used to describe a call that completes entirely by a panel switch, and does not make use of human operators
• Direct Mechanical - A call that completes using revertive pulse, without the use of a tandem office as an intermediate switching point.
• Full Selector - Analogous to "full mechanical", although its use strongly implies revertive pulse signaling.
• Machine Switching - Used to generally describe methods of switching without the use of an operator. Did not necessarily imply the use of the panel system, although the panel system was one of the type of "machine switching" system.