Ringing is a

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

signal that causes a bell or other device to alert a

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 ...

subscriber to an incoming

telephone call A telephone call is a connection over a telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and interne ...

. Historically, this entailed sending a high-voltage

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

over the telephone line to a customer station which contained an electromagnetic bell. It is therefore also commonly referred to as ''power ringing'', to distinguish it from another signal, audible ringing, or ringing tone, which is sent to the originating caller to indicate that the destination telephone is in fact ringing.

Specifications

In landline telephones, bells or ringtones are rung by impressing a 60 to 105-volt RMS 20-Hertz sine wave across the

tip and ring Tip and ring are the two conductors or sides of a telephone line. Their names are derived from the telephone plugs used for connecting telephone calls in manual switchboards. One side of the line is connected to the metal ''tip'' of the plug, and ...

conductors of the subscriber line, in series with the (typically) −48 VDC loop supply. This signal is produced by a ringing generator at the central office. When the switching system directs a call to a particular subscriber line, a relay on the

line card A line card or digital line card is a modular electronic circuit designed to fit on a separate printed circuit board (PCB) and interface with a telecommunications access network. A line card typically interfaces the twisted pair cable of a plain ...

connects the ringing generator to the subscriber line. The exchange also sends a

ringing tone Ringing tone (audible ringing, also ringback tone) is a signaling tone in telecommunication that is heard by the originator of a telephone call while the destination terminal is alerting the receiving party. The tone is typically a repeated cade ...

to the

calling party The calling party (in some contexts called the "A-Number") is a person who (or device that) initiates a telephone call. The person who, or device that, receives a telephone call is the called party (or callee or B-party). In some countries, it is ...

. When the

called party The called party (in some contexts called the "B-Number") is a person who (or device that) answers a telephone call. The person who (or device that) initiates a telephone call is the calling party. In some situations, the called party may number m ...

answers by taking the telephone

handset A handset is a component of a telephone that a user holds to the ear and mouth to receive audio through the receiver and speak to the remote party using the built-in transmitter. In earlier telephones, the transmitter was mounted directly on ...

off the

switchhook A telephone hook or switchhook is an electrical switch which indicates when the phone is hung up, often with a lever or magnetic button inside the cradle or base where a telephone handset resides. It takes its name from old wooden wall telephone ...

, the subscriber's telephone draws

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...

from the central office battery. This current is sensed by the line card and the ringing relay is de-energized.

Multi-party lines

On multi-party lines, ringers would typically be connected from one side of the two-wire line to ground; a "tip party" and "ring party" would have bells connected from opposite sides of the line. On a two-party service, each user would not hear ringing for calls to the other party. Some 20th-century independent telephone companies deployed four-party lines which used differing frequencies for selective ringing of individual parties (the four possible combinations were 20 Hz or 30 Hz from tip to ground, 20 Hz or 30 Hz from ring to ground). If additional parties were added to the same line,

distinctive ring Distinctive ring, marketed under a variety of names, is a service offered by a telephone company that establishes additional telephone numbers on the same line as an existing number, each number ringing with a distinctive ringing pattern. Typically ...

ing patterns would need to be used to identify the called subscriber; these were audible to the multiple users on the line.

Ringing generator

A ring generator or ringing voltage generator is a device which outputs 20 cycle sinusoidal AC at up to 110 volts peak to power bells or annunciators in one or more telephone

extensions Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * E ...

. The output stops if a handset is taken off the hook. In terminology devised by

phone phreak Phreaking is a slang term coined to describe the activity of a culture of people who study, experiment with, or explore telecommunication systems, such as equipment and systems connected to public telephone networks. The term ''phreak'' is a ...

s, a ringing generator is a magenta box. The device can be used to simulate an incoming call by applying the AC ringing signal voltage to a POTS line to make the telephones on that line ring. A magenta box in conjunction with an

orange box An orange box is a piece of hardware or software that generates caller ID frequency-shift keying (FSK) signals to spoof caller ID information on the target's caller ID terminal. See also * Blue box A blue box is an electronic device tha ...

(which emulates the

caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call is ...

signal to create falsified data) is called a

vermilion box The vermilion box is a hypothetical portable improvised line emulator. Its function is to spoof not only caller ID but every other aspect of an incoming telephone call, including ringing and DC line voltage. Typically, the user physically discon ...

. The hardware also has multiple legitimate applications. While a

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 ...

includes a central source of ringing voltage at the switchboard, 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 ...

or telephone-based

intercom An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building or small collection of buildings which functions independently of the public telephon ...

must provide a local source of AC ringing voltage. Theatrical performances often deploy a ringing telephone on-stage as a stage prop. An

analog telephone adapter An analog telephone adapter (ATA) is a device for connecting traditional analog telephones, fax machines, and similar customer-premises devices to a digital telephone system or a voice over IP telephony network. An ATA is often built into a sma ...

for

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 ...

applications has to provide its own ringing voltage generator and other

line signaling Line signaling is a class of telecommunications signaling protocols. Line signaling is responsible for off-hook, ringing signal, answer, ground start, on-hook unidirectional supervision messaging in each direction from calling party to called pa ...

services for standard telephone extensions. The hardware may also be useful to technicians for test purposes. Stand-alone ringing voltage generators are commercially manufactured; ring generators are also pre-built for inclusion in other telecommunications equipment and various circuits published by hobbyists to generate or detect ringing voltage for analogue telephony. A closed system, such as an intercom or

, need not comply with standards for ringing if it does not use standards-compliant telephone extensions. Some office telephones replace the bells with separately-wired low-voltage DC buzzers or use entirely custom-designed extensions which only work with one manufacturer's switchboard. These avoid the need to generate 20 Hz 90V sinusoidal AC, but are not compatible with standard telephone ringers.

Ring forward and ringback

Ring forward is a brief signal of about 100 ms duration sent during an established connection on a trunk line between central offices by the calling operator to recall the operator at the receiving office. If the trunk line is not metallic, an equivalent on-hook condition is sent that is converted at the receiving trunk equipment to a recall signal. In contrast to ring forward, the ringback signal is originated from the receiving or called end of a trunk line during an established connection, to recall the originating operator. The signal is also sent by a coin line operator to recall a customer at a pay station after the customer hangs up, for example to inform the customer of time and charges of the completed call.

References

{{Authority control Phreaking boxes Telephony signals