Pulse dialing

Pulse dialing is a signaling technology in telecommunications in which the direct current flowing in the telephone local loop circuit is interrupted in a pattern according to a coding system for each signal (digit) transmitted. This lends the technology the name loop disconnect signaling. In the most common variant of pulse dialing, decadic dialing, each of the ten Arabic numerals is encoded in a sequence of up to ten current pulses. The most common version decodes the digits 1 through 9 as one to nine pulses, respectively, and the digit 0 as ten pulses. Historically, the most common device to produce such pulse trains is the rotary dial of the telephone, lending the technology another name: rotary dialing. The pulse repetition rate was historically determined based on the response time needed for electromechanical switching systems to operate reliably. Most telephone systems used the nominal rate of ten pulses per second, but operator dialing within and between central offices often used pulse rates up to twenty per second.