Operator signaling

In telephony

Telephony

In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

, ringdown is a method of signaling an operator in which telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 ringing current is sent over the line

Telephone line

A telephone line or telephone circuit is a single-user circuit on a telephone communication system...

 to operate a lamp or cause the operation of a self-locking relay

Relay

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

 known as a drop. Ringdown (a) is used in manual operation, as distinguished from dialing, (b) uses a continuous or pulsed ac signal transmitted over the line, and (c) may be used with or without a switchboard

Telephone switchboard

A switchboard was a device used to connect a group of telephones manually to one another or to an outside connection, within and between telephone exchanges or private branch exchanges . The user was typically known as an operator...

. The term ringdown originated in magneto telephone signaling in which cranking the magneto in a telephone set would not only ring its bell but also cause a drop to fall down at the central office 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, had 400+ subscribers, and converted to dial service in October 1983.

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. There is no dialing and phones 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.

In some circumstances, the electronics that operate ringing are part of a key service unit

Key telephone system

A business telephone system is any of a range of a multiline telephone systems typically used in business environments, encompassing systems ranging from small key systems to large scale private branch....

. This is the electronics box that operates a multi-line key telephone system. In the wire spring relay

Wire spring relay

A wire spring relay is a type of relay, primarily manufactured by the Western Electric Company for use by the Bell System in electromechanical telephone exchanges. It was licenced for use around the world, and was commonplace in Japan...

 vintage Bell System

Bell System

The Bell System was the American Bell Telephone Company and then, subsequently, AT&T led system which provided telephone services to much of the United States and Canada from 1877 to 1984, at various times as a monopoly. In 1984, the company was broken up into separate companies, by a U.S...

 1A2 key service units, a model 216 automatic ringdown was used to operate the circuit. In the 400-series units, there are a number of different KTUs that operate (supervise) a ringdown including a 415. In other situations, the ringdown is powered and operated by equipment inside the central office

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

.

In the case of enterprises with a PBX switch, the ringdown can be operated by the PBX switch. 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 dialtone to the calling extension: it only looks for on-hook

On-hook

In telephony, the term on-hook has the following meanings:# The condition that exists when a telephone or other user instrument is not in use, i.e., when idle waiting for a call. Note: on-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a switchhook...

 or off-hook

Off-hook

In telephony, the term off-hook has the following meanings:# The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece , which hung...

 status.

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 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

Control tower

A control tower, or more specifically an Air Traffic Control Tower , is the name of the airport building from which the air traffic control unit controls the movement of aircraft on and around the airport. Control towers are also used to control the traffic for other forms of transportation such...

 to the airport's fire station or fire dispatch center.

Example: Independent System Operator (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 (CPC

CPC

- Organizations :* Confirmation Preperation Class* California Preparatory College* Canadian Parachute Centre* Canadian Paralympic Committee* Center for Plant Conservation* Children's Psychiatric Center, Monmouth County, NJ USA* Climate Prediction Center...

) signal.

PLAR

PLAR stands for Private Line Automatic Ringdown. It is a type of analog signalling often used with telephone based intercom

Intercom

An intercom , talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles...

 systems. When a device is taken off-hook, it applies a ringing voltage to the circuit. Other devices on the same pair will ring. Then, when another device is answered, a call will be maintained over the circuit at normal voltage. The telephone company switch is not involved in the process, making this a private line.

External links

• The Last Ringdown, 1980 documentary on the Bryant Pond
  Woodstock, Maine
  Woodstock is a town in Oxford County, Maine, United States. The population was 1,307 at the 2000 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.-Geography:...
  
   Telephone Company
• PLAR Configuration Example, on Cisco
  Cisco
  Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...
  
   Call Manager (CUCM) v.6