Hook flash

Last updated

On analog telephone lines with special services, a flash or register-recall signal is used to control functions on the public telephone exchange, PBX or VoIP ATA.

The term "register-recall" in Europe refers to sending a discrete signal to alert the "register" — the logical system controlling a telephone exchange, that it should accept commands from the end user in the middle of a call. The register was normally disconnected from the circuit once a call was setup.

In contemporary telephone systems, the functions of the register are carried out by software and computer hardware, but in previous generations of electromechanical exchanges, using technology such as crossbar or reed relay, the register was often a system of analog electronics or even relay logic. [1]

The term "flash" or "hook flash" is commonly used in North America, while in Europe a similar signal is referred to as a register-recall [2] or more commonly "Recall" or simply the "R" button. These signals perform similar functions, but are not necessarily identical.

The flash signal briefly disconnects the local loop circuit by momentarily depressing the hook switch or using a dedicated button. In systems influenced by American standards, the switching system will accept quite a long disconnection time, within a duration between 300  ms and 1000 ms, typical of a manual hook flash. In most systems based on European standards, a precisely defined loop disconnect pulse is used, typically 100 ms or 120 ms in duration, similar to a single pulse on a pulse dialing telephone. These systems are similar, but may be mutually incompatible.

The longer flash time programmed on a North American telephone, or a manual hook flash, may cause a European switch to clear the line, while a short pulse from a European phone may be ignored by a North American switching system. Many modern telephones, sold across multiple markets, allow the end user to define the flash time in software or with a switch setting. For example, some devices allow this to be set between 90 ms and 1000 ms. This means that the phone can be configured to be used with various public PSTN networks, PABX and business systems, or devices like analog telephone adaptors (ATAs) used for connecting simple analog telephones to Voice over IP (VoIP) services.

Typical standard phone used with Centrex. Note the "Recall" button and the red Message Waiting lamp to the left of the keypad. ATTtelephone-large.jpg
Typical standard phone used with Centrex. Note the "Recall" button and the red Message Waiting lamp to the left of the keypad.
Manual Hook Flash to enable call switching on a German desk phone (FeTAp 711 model). Gabelschlag.gif
Manual Hook Flash to enable call switching on a German desk phone (FeTAp 711 model).
European phone with R button Tastentelefon Signo.jpeg
European phone with R button

A common use of a hook flash for special action is to switch to another incoming call with the call waiting service.

It is also commonly used for placing calls on hold, initiate inquiry, conference calls, or for call transfer to other extensions in a PABX

Another use is to indicate a request for voice conferencing, for example, a user may use a procedure like the following to initiate three-way calling. This is the typical procedure in most North American networks and some office systems:

  1. Pick up phone handset (causing the line to be off-hook).
  2. Hear a dial tone.
  3. Dial the first number and greet the first party.
  4. Press the hook flash button (or quickly tap the on-hook sensor on the phone).
  5. Hear a stutter dial tone (a series of beeps followed by another dial tone).
  6. Dial the second number and greet the second party.
  7. Press the hook flash button again.

The second "flash" signals the Central Office Switch to link the two active conversations, so that all three parties are connected to the same logical telephone line.

In European networks an “R” button is used in combination with touch tone digits to select various call handling functions. For example:

Call Waiting:

Pressing the R button during a call usually places the call on hold and returns a dial tone. A second number can then be dialed. Calls can then be toggled between with R2 or conferenced together with R3.

On Centrex lines, PBX systems and VoIP ATAs a hook flash or the R-button is also used to perform call transfer (blind or with an enquiry) on analog extensions.

During a call the hook is flashed (manually or Flash or R is pressed) placing the current call on hold and returning a dial tone. A new number is then dialed and when the phone is hung up, the call is transferred. In European systems, pressing R before hanging up, typically retrieves the call on hold and cancels the process without transferring the call.

Some PBX systems, notably in Europe, use an Earth Recall. This signal connects one leg of the telephone circuit to the ground momentarily to signal the exchange. It's usually not used in public two-wire networks, but was common in analog office systems. Many European telephones have a switch to configure the R button to perform this function instead of a timed break recall. [3]

A related service was often found on payphones in Europe and some other parts of the world where a Follow on Call (FC) button was often provided. While similar in some ways to a hook flash, this was quite different. Rather than simply flashing the hook, the phone would go completely on-hook (hanging up) several seconds and would present a new dial tone, while retaining a credit balance on the phone (coins or card). This allowed the user to make a second call without needing to collect unused coins or re-insert their card on phones that used prepaid cards. It is not hook flash signaling, but rather just hanging up the line.

History

The switchhook is the device that senses whether the handset or receiver is in its cradle. The term "flash" originated from the cord circuit of the early telephone switchboard that telephone company operators used to connect calls. The calling party and called party each had an indicator light on the cord circuit. When the subscriber cycled the telephone on-hook/off-hook, the light would flash. Actors in old movies often demonstrate this method, seeking the operator's attention. The user performs a tap-tap-tap. When an operator comes on the line, the actor says, "Hello? Operator? We've been cut off." Then the operator attempts to reestablish the connection. The flashing light of this early equipment is the origin of the phrase "flashing the switchhook".

Centrex telephones added a hook-flash button in the 1960s after some users attempted the attendant-recall function incorrectly and disconnected their calls inadvertently.

Related Research Articles

<span class="mw-page-title-main">DTMF</span> Telecommunication signaling system

Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized as ITU-T Recommendation Q.23. It is also known in the UK as MF4.

<span class="mw-page-title-main">Telephone</span> Telecommunications device

A telephone, colloquially referred to as a phone, 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 electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user. The term is derived from Ancient Greek: τῆλε, romanized: tēle, lit. 'far' and φωνή, together meaning distant voice.

<span class="mw-page-title-main">Pulse dialing</span>

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 disconnect dialing. In the most common variant of pulse dialing, decadic dialing, each of the ten Arabic numerals are encoded in a sequence of up to ten 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.

In telephony, ringdown is a method of signaling an operator in which telephone ringing current is sent over the line to operate a lamp or cause the operation of a self-locking relay known as a drop.

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 intimately linked to the invention and development of the telephone.

Plain Old Telephone Service (POTS), or Plain Ordinary Telephone System, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. Originally POTS stood for Post Office Telephone Service as early phone lines in most parts of the world were operated directly by the local Post Office.

A dial tone is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is working and is ready to initiate a telephone call. The tone stops when the first dialed digit is recognized. If no digits are forthcoming, the partial dial procedure is invoked, often eliciting a special information tone and an intercept message, followed by the off-hook tone, requiring the caller to hang up and redial.

<span class="mw-page-title-main">Blue box</span> Device for hacking telephone networks

A blue box is an electronic device that produces tones used to generate the in-band signaling tones formerly used within the North American long-distance telephone network to send line status and called number information over voice circuits. During that period, charges associated with long-distance calling were commonplace and could be significant, depending on the time, duration and destination of the call. A blue box device allowed for circumventing these charges by enabling an illicit user, referred to as a "phreaker" to place long-distance calls, without using the network's user facilities, that would be billed to another number or dismissed entirely by the telecom company's billing system as an incomplete call. A number of similar "color boxes" were also created to control other aspects of the phone network.

<span class="mw-page-title-main">Telephone call</span> Connection between two or more people over a telephone network

A telephone call or telephone conversation, also known as a phone call or voice call, is a connection over a telephone network between the called party and the calling party. Telephone calls started in the late 19th century. As technology has improved, a majority of telephone calls are made over a cellular network through mobile phones or over the internet with Voice over IP. Telephone calls are typically used for real-time conversation between two or more parties, especially when the parties cannot meet in person.

Call waiting is a telephone service where a subscriber can accept a second incoming telephone call by placing an in-progress call on hold—and may also switch between calls. With some providers it can be combined with additional features such as conferencing, call forwarding, and caller ID. Call waiting is intended to alleviate the need to have more than one telephone line or number for voice communications.

The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists of telephone lines, fiber-optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables interconnected by switching centers, such as central offices, network tandems, and international gateways, which allow telephone users to communicate with each other.

In telephony, an automated attendant allows callers to be automatically transferred to an extension without the intervention of an operator/receptionist. Many AAs will also offer a simple menu system. An auto attendant may also allow a caller to reach a live operator by dialing a number, usually "0". Typically the auto attendant is included in a business's phone system such as a PBX, but some services allow businesses to use an AA without such a system. Modern AA services can route calls to mobile phones, VoIP virtual phones, other AAs/IVRs, or other locations using traditional land-line phones or voice message machines.

<span class="mw-page-title-main">Business telephone system</span> Telephone system typically used in business environments

A business telephone system is a telephone system typically used in business environments, encompassing the range of technology from the key telephone system (KTS) to the private branch exchange (PBX).

Direct inward dialing (DID), also called direct dial-in (DDI) in Europe and Oceania, is a telecommunication service offered by telephone companies to subscribers who operate private branch exchange (PBX) systems. The feature provides service for multiple telephone numbers over one or more analog or digital physical circuits to the PBX, and transmits the dialed telephone number to the PBX so that a PBX extension is directly accessible for an outside caller, possibly by-passing an auto-attendant.

Loop start is a telecommunications supervisory protocol between a central office or private branch exchange (PBX) and a subscriber telephone or other terminal for the purpose of starting and terminating a telephone call. 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.

<span class="mw-page-title-main">AT&T Merlin</span> Corporate telephone system

AT&T Merlin is a corporate telephone system by American Telephone and Telegraph (AT&T) that was introduced in late 1983, when it was branded American Bell Merlin. After the breakup of AT&T in 1984, it was rebranded and later also supplied by Lucent and Avaya.

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 and lines are the idle and busy states, seizure, and disconnect. The states are indicated by various electrical signals and electrical conditions depending on the type of circuit, the type of terminating equipment, and the type of intended service.

Ringing is a telecommunication signal that causes a bell or other device to alert a telephone subscriber to an incoming telephone call. Historically, this entailed sending a high-voltage alternating current 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.

<span class="mw-page-title-main">Push-button telephone</span> Telephone which has buttons or keys for dialing

A push-button telephone is a telephone that has buttons or keys for dialing a telephone number, in contrast to a rotary dial used in earlier telephones.

<span class="mw-page-title-main">Telephone exchange</span> Interconnects telephones for calls

A telephone exchange, also known as a telephone switch or central office, is a crucial component in the public switched telephone network (PSTN) or large enterprise telecommunications systems. It facilitates the interconnection of telephone subscriber lines or digital system virtual circuits, enabling telephone calls between subscribers.

References

  1. ↑ https://www.etsi.org/deliver/cept/20/2009CS.PDF [ bare URL PDF ]
  2. ↑ https://www.etsi.org/deliver/cept/20/2009CS.PDF [ bare URL PDF ]
  3. ↑ "GLOSSARY OF TELEPHONE TERMS - MF, Code "C"".
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.