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The Panel switching system was an early type of automatic telephone exchange for primarily urban service, first introduced in the Bell System in the 1920s and replaced by modern systems during the 1970s. It was developed by Western Electric Labs, later called Bell Labs, in the U.S. in parallel with the Rotary system at International Western Electric in Belgium before World War I〔Fagen pages 581, 607〕 which was used in Europe. Both systems had many features in common. The first Panel exchange was installed at the Mulberry Central Office in Newark, New Jersey.〔page 582〕 It was placed in service on January 16, 1915. It was a semi-automatic system using telephones without a dial. Operators answered calls and keyed the station number into the panel switch. The next installation was in the Waverly central office on June 12 of the same year, also in Newark. The Panel Machine Switching System was named for its tall panels covered with 500 rows of terminals. Each panel had an electric motor to drive its, usually sixty, selectors by electromagnetically controlled clutches. The selector was similar in effect to a stepping switch though it moved continuously rather than in steps. Each selector had five brushes, each of which could select from 100 terminals arranged in groups. Pulses were sent back from the selector to a register, which had received the dialed digits, rather than forward as in the Strowger switch step-by-step (SXS) system, hence the signaling was called ''revertive'' pulsing. ==Telephone numbering== As in the SXS system, each installed office could handle up to 10,000 numbered lines, requiring four digits for a single subscriber station. The panel system was designed to interconnect the offices of a city or a local calling area. Each office was assigned a two-digit code (later three) office prefix. Callers dialed the office code followed by the station number. In most situations this led to six-digit (later seven) numbers. But from the beginning the panel system handled seven-digit numbers (later eight), for two reasons. Party line numbers were listed with one of the letters J, M, R, and W following the line number. The caller dialed the office code, the line number, and the digit corresponding to the letter. The panel system was designed to work with manual offices of up to 10,500 lines. To call a line in a manual office, callers dialed the office code followed by the line number. For lines 10,000 and up, callers therefore dialed the office code and a five-digit line number. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「panel switch」の詳細全文を読む スポンサード リンク
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