Panel switch

Panelother exchange typespanel dial systemsPanel Machine Switching SystemPanel systempanel type
The Panel Machine Switching System is an early type of automatic telephone exchange for urban service, introduced in the Bell System in the 1920s.wikipedia
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Rotary system

RotaryRotary exchanges
It was developed by Western Electric Laboratories, the forerunner of Bell Labs, in the U.S., in parallel with the Rotary system at International Western Electric in Belgium before World War I. Both systems had many features in common.
7-A Machine Switching System, it was developed in Belgium by International Western Electric, a subsidiary of American Telephone and Telegraph (AT&T), at the same time when AT&T's American engineering division, Western Electric, was developing the Panel switch in the United States.

Telephone exchange

exchangescentral officeexchange
The Panel Machine Switching System is an early type of automatic telephone exchange for urban service, introduced in the Bell System in the 1920s.
Exchanges based on the Strowger switch were eventually challenged by other exchange types and later by crossbar technology.

Automatic Electric

Automatic Electric CompanyStrowger Automatic Telephone Exchange CompanyAutomatic Telephone & Electric Co. Ltd
As in the Strowger system, each central office could address up to 10,000 numbered lines, requiring four digits for each subscriber station.
Automatic switches proliferated in independent telephone companies in the 1910s and 1920s, well before the Bell System started deployment of Panel switch technology in the 1920s.

Newark, New Jersey

NewarkNewark, NJCity of Newark
The first Panel-type exchanges were placed in service in Newark, New Jersey, on January 16, 1915 at the Mulberry central office, and on June 12 in the Waverly central office.
In 1915, the Bell System under ownership of American Telephone and Telegraph Company (AT&T) tested newly developed panel switching technology in Newark when they

Sender

Simultaneously, a sender was selected, which provided dial tone for the caller once their line was found. While the Strowger (step-by-step) switch moved under direct control of dial pulses that came from the telephone dial, the more sophisticated Panel switch had senders, which registered and stored the digits that the customer dialed, and then translated the received digits into numbers appropriate to drive the selectors to their desired position: District Brush, District Group, Office Brush, Office Group, Incoming Brush, Incoming Group, Final Brush, Final Tens, Final Units.
This was developed in the US by the Bell System and was first widely used in the Panel Machine Switching System.

Common control

The first fully machine-switching Panel systems using common control principles were placed in service in Omaha, Nebraska in December 1921, followed by the PEnnsylvania exchange in New York City in October 1922.
Early semi-mechanical installations with common control components existed, for example rotary systems in Sweden and France in 1915, and the first panel switches in Newark, New Jersey, also in 1915.

Telephone switchboard

switchboardswitchboardscentral switchboard
Similar to the divided-multiple telephone switchboard, the panel system consisted of an originating section and a terminating section.
Conversion to Panel switch and other automated switching systems first eliminated the "B" operator and then, usually years later, the "A".

Number One Crossbar Switching System

1XBNo. 1 Crossbar1XB switch
The Number One Crossbar, which was the first successor to the Panel system also used this method of signaling exclusively, until later upgrades introduced newer signaling such as Multi-frequency signaling.
Its switch fabric used the new electromechanical crossbar switch to implement the topology of the panel switching system of the 1920s.

Panel call indicator

Coded-Call IndicatorCoded Call Indicatorindicator
In areas with mostly machine switches and only a few manual switchboards, Panel Call Indicator (PCI) signaling transmitted the called number to the "B" Board Machine Incoming operator, which lit lamps on the operator's desk at the terminating manual office.
Originally designed along with the panel type telephone office, PCI was intended to allow subscribers in fully automated exchanges to dial numbers in manual offices the same way they dialed numbers in their own exchange.

Direct distance dialing

direct dialdirect distance dialIDDD
The introduction of direct distance dialing (DDD) in the 1950s required the addition of automatic number identification equipment for centralized automatic message accounting.
With semiautomatic operation analogous to the early days of the panel switch, the operator in the originating city used a multifrequency keypad to dial an access code to connect to the correct city and to send the seven digit number to incoming equipment at the terminating city.

Rotary dial

rotary telephonedialrotary phone
While the Strowger (step-by-step) switch moved under direct control of dial pulses that came from the telephone dial, the more sophisticated Panel switch had senders, which registered and stored the digits that the customer dialed, and then translated the received digits into numbers appropriate to drive the selectors to their desired position: District Brush, District Group, Office Brush, Office Group, Incoming Brush, Incoming Group, Final Brush, Final Tens, Final Units.
Hence the first Panel automatic exchanges cutover in 1915 in Newark, New Jersey used "semiautomatic" operation with the local operator keying the number for the caller.

Pulse dialing

dial pulsepulse diallingpulse dial
While the Strowger (step-by-step) switch moved under direct control of dial pulses that came from the telephone dial, the more sophisticated Panel switch had senders, which registered and stored the digits that the customer dialed, and then translated the received digits into numbers appropriate to drive the selectors to their desired position: District Brush, District Group, Office Brush, Office Group, Incoming Brush, Incoming Group, Final Brush, Final Tens, Final Units.
These included access lines to the Panel switch in the 1920s, Crossbar systems, the later version (7A2) of the Rotary system, and the earlier 1970s stored program control exchanges.

Automatic message accounting

Centralized Automatic Message Accountingautomatic message accountcall accounting
The introduction of direct distance dialing (DDD) in the 1950s required the addition of automatic number identification equipment for centralized automatic message accounting.
Electromechanical pulse counters counted message units for message rate service lines in panel switches and similar exchanges installed in the early and middle 20th century.

Bell System

Bell Operating CompanyBell Operating CompaniesBell Telephone
The Panel Machine Switching System is an early type of automatic telephone exchange for urban service, introduced in the Bell System in the 1920s.

Bell Labs

Bell LaboratoriesBell Telephone LaboratoriesAT&T Bell Laboratories
It was developed by Western Electric Laboratories, the forerunner of Bell Labs, in the U.S., in parallel with the Rotary system at International Western Electric in Belgium before World War I. Both systems had many features in common.

Relay

relayslatching relayelectric relay
As the subscriber dialed, relays in the sender counted and stored the digits for later usage.

Reorder tone

reorderall circuits busy" tonecircuit busy
If all the trunks were busy, the selector hunted to the end of the group, and finally sent back an "all circuits busy" tone.

Busy signal

busy toneengaged tonebusy
If the called subscriber's line was busy, the final selector sent a busy signal back to the called party to alert them that the caller was on the phone and could not accept their call.

Party line (telephony)

party lineparty linestelephone party line
In areas that served party lines, the system accepted an additional digit for party identification.

Line signaling

line signallingsupervisionline
Supervision (line signaling) was supplied by a District circuit, similar to the plug and light cord circuit that plugged into a line jack on a switchboard.

Cord circuit

junctors
Supervision (line signaling) was supplied by a District circuit, similar to the plug and light cord circuit that plugged into a line jack on a switchboard.

Phone connector (audio)

headphone jackTRRSTRS connector
Supervision (line signaling) was supplied by a District circuit, similar to the plug and light cord circuit that plugged into a line jack on a switchboard.

On- and off-hook

off-hookon-hookon hook
The line circuit consisted of a line relay on the originating side to indicate that a customer had gone off-hook, and a cutoff relay to keep the line relay from interfering with an established connection.

Payphone

pay phonepayphonespublic telephone
Some District frames were equipped with the more complex supervisory and timing circuits required to generate coin collect and return signals for handling calls from payphones.

Flat rate

flat feeflat-rateflat fare
Many of the urban and commercial areas where Panel was first used had message rate service rather than flat rate calling.