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It is the simplest of the telephone signaling systems, and uses the presence or absence of loop current to indicate the off-hook and on-hook loop states, respectively. It is used primarily for subscriber line signaling. An extension of the protocol that adds disconnect supervision is often called kewlstart.
Analog current loops were historically occasionally carried between buildings by dry pairs in telephone cables leased from the local telephone company. 4–20 mA loops were more common in the days of analog telephony. These circuits require end-to-end direct current (DC) continuity, and unless a dedicated wire pair was hardwired, their use ...
On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair. When an off-hook condition persists without dialing, for example because the handset has fallen off or the cable has been flooded, it is treated as a permanent loop or permanent signal.
A loop line or loop around is a telephone company test circuit. The circuit has two associated phone numbers. When one side of the loop is called (side A), the caller receives a test tone of approximately 1000 Hz (milliwatt test). When the second number (side B) is called, it produces dead silence, but the party on side A hears the milliwatt ...
The model 500 rotary dial telephone by Western Electric was a pulse-dialing instrument. Pulse dialing is a signaling technology in telecommunications in which a direct current local loop circuit is interrupted according to a defined coding system for each signal transmitted, usually a digit. This lends the method the often used name loop ...
The local loop may terminate at a circuit switch owned by a competitive local exchange carrier and housed in a point of presence (POP), which typically is an incumbent local exchange carrier telephone exchange. A local loop supports voice and/or data communications applications in the following ways: analog voice and signaling used in ...
An open switching interval (OSI), also called open loop disconnect, is a period of time for which the central office battery is removed from a telephone line. The removal of battery may be used to signal the disconnection (disconnect supervision) of the telephone circuit.
Plain old telephone service (POTS), or publicly offered telephone service, [1] is a retronym for voice-grade telephone service that employs analog signal transmission over copper loops. The term POTS originally stood for post office telephone service , [ citation needed ] as early telephone lines in many regions were operated directly by local ...