Ringdown
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telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
, ringdown is a method of
signaling In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
an operator in which
telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
ringing current is sent over the line to operate a lamp or cause the operation of a self-locking
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switch ...
known as a ''drop''. Ringdown is used in manual operation, and is distinguished from automatic signaling by dialing a number. The signal consists of a continuous or pulsed alternating current (AC)
signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
transmitted over the line. It may be used with or without a
telephone switchboard A telephone switchboard was a device used to connect circuits of telephones to establish telephone calls between users or other switchboards, throughout the 20th century. The switchboard was an essential component of a manual telephone exchange, ...
. The term originated in
magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...
telephone signaling in which cranking the magneto generator, either integrated into the telephone set or housed in a connected ringer box, would not only ''ring'' its bell but also cause a drop to fall ''down'' at the
telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...
switchboard, marked with the number of the line to which the magneto telephone instrument was connected. The last ringdown telephone exchange in the United States was located at
Bryant Pond, Maine Woodstock is a town in Oxford County, Maine, United States. The population was 1,352 at the 2020 census. The village of Bryant Pond, on State Route 26 in the northern part of Woodstock, is the town's urban center and largest settlement. Histor ...
, had 400+ subscribers, and converted to dial service in October 1983.


Ringdown operator

In telephone systems where calls from distant automated exchanges arrive for manual subscribers or
non-dialable point In conventional landline telephony, a non-dialable toll point or toll station was a lone station or line serving a rural subscriber many miles from the nearest central office. As it had no home telephone exchange and therefore no local calling area ...
s, there often would be a ringdown operator (reachable from the distant operator console by dialling NPA+181) who would manually ring the desired subscriber on a party line or toll station. On some systems, this function was carried out by the inward operator (NPA+121). In both cases, this is a telephone operator at the destination who provides assistance solely to other operators on inbound toll calls; the ringdown operator nominally cannot be dialed directly by the subscriber.


Non-operator use

In an application ''not'' involving a telephone operator, a two-point automatic ringdown circuit, or ringdown, has a telephone at each end. When the telephone at one end goes off-hook, the phone at the other end instantly rings. No dialing is involved and therefore telephone sets without dials are sometimes used. Many ringdown circuits work in both directions. In some cases a circuit is designed to work in one direction only. That is, going off-hook at one end (end A) rings the other (end B). Going off-hook at end B has no effect at end A. Ringdown features are often part of a
key telephone system A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...
. In the
wire spring relay A wire spring relay is a type of relay, that has springs made from drawn wires of nickel silver, rather than cut from flat sheet metal as in the flat-spring relay. This class of relays provided manufacturing and operating advantages over previous d ...
key service units of the
Bell System The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over one hundr ...
1A2, a model 216 automatic ringdown was used to operate the circuit. In the 400-series units, a number of different KTUs operate (supervise) a ringdown, including the model 415. In other situations, the ringdown is powered and operated by equipment inside the
telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...
. In the case of enterprises with a
private branch exchange A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...
(PBX) switch, the ringdown can be operated by the PBX key. The switch is programmed to ring a specific extension (the called phone) when a defined extension (the calling phone) goes off-hook. The PBX does not offer dial tone to the calling extension: it only detects
on-hook In telephony, on-hook and off-hook are two states of a communication circuit. On subscriber telephones the states are produced by placing the handset onto or off the hookswitch. Placing the circuit into the off-hook state is also called ''seizing th ...
or
off-hook In telephony, on-hook and off-hook are two states of a communication circuit. On subscriber telephones the states are produced by placing the handset onto or off the hookswitch. Placing the circuit into the off-hook state is also called ''seizing th ...
status.
Voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of speech, voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms In ...
adapters can be networked and configured to provide automatic ringdown by selecting a dial plan which replaces the empty string with a predefined number or SIP address, dialed immediately. (Some Cisco VoIP phones and analog adapters treat a dial plan of (S0 <:1234567890>) as a hotline configuration which dials 1-234-567890 zero seconds after the telephone is taken off-hook, for instance).Getting to Know Dial Plans Sequences
Document ID #108719, Cisco, Dec 12, 2008 These circuits are used: * over high-volume routes where one site calls another very frequently. :''Example: an information desk and the information desk staff supervisor's desk.'' * where a tamper-proof ability to call from one point to another is needed. :''Example: a phone used to summon a taxicab to an airport or hotel.'' * where a limited ability to contact one entity (but no ability to make outside calls) is desired. :''Example: a "house phone" in a hotel lobby to the live operator at the hotel's switchboard'' * where the public, or users that are not trained in using a specific office telephone system, must place calls. :''Example: the after-hours phone to reach the watchman from the front door at a warehouse.'' * in locations where emergencies are handled and the time required to dial digits would cause an unacceptable delay in handling of an emergency. :''Example: an airport
control tower Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...
to the airport's fire station or fire dispatch center.'' :''Example:
Independent System Operator A regional transmission organization (RTO) in the United States is an electric power transmission system operator (TSO) that coordinates, controls, and monitors a multi-state electric grid. The transfer of electricity between states is considered i ...
(ISO) communication to a power plant.'' * in situations where the called party needs to be certain of who is calling. :''Example: a hospital emergency department and an ambulance dispatch center.'' In some cases, automatic ringdown circuits have one-to-many configurations. When one phone goes off-hook, a group of phones is made to ring simultaneously. In cases where one or both ends of the circuit terminate in a key telephone system, a well designed system will have no hold feature on the ringdown circuit unless supervision provides a
Calling Party Control In telecommunication, supervision is the monitoring of a telecommunication circuit for telephony to convey to an operator, user, or a switching system, information about the operational state of the circuit. The typical operational states of trunks ...
(CPC) signal.


PLAR

Private line automatic ringdown (PLAR) is a type of analog signaling often used in telephone-based systems. When a device is taken off-hook, ringing voltage is automatically applied to a circuit to alert other stations on the line. When answered on another station, a call is maintained over the circuit. The telephone company switch is not involved in the process, making this a private line.


See also

*
Courtesy phone A courtesy telephone is a telephone located in airport terminals, large train stations, hotel lobbies, and other places where many travellers are expected, which is used to relay messages to a specific person. It is typically used in connection w ...
*
Dedicated line In computer networks and telecommunications, a dedicated line is a communications cable or other facility dedicated to a specific application, in contrast with a shared resource such as the telephone network or the Internet. It is a communication ...


References

*


External links


The Last Ringdown
1980 documentary on the Bryant Pond Telephone Company
PLAR Configuration Example
on
Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...
Call Manager Call or Calls may refer to: Arts, entertainment, and media Games * Call, a type of betting in poker * Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage Music and dance * Call (band), from Lahore, Paki ...
( CUCM) v.6 {{Telecommunications Communication circuits Telephony equipment