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67-408: When dialing from a land-line telephone , the telephone number is encoded and transmitted across the telephone line in form of dual-tone multi-frequency signaling (DTMF). The tones control the telephone system by instructing the telephone switch where to route the call. These control tones are sent over the same channel , the copper wire, and in the frequency range (300 Hz to 3.4 kHz) as

134-606: A disruptive technology that is rapidly replacing traditional telephone network infrastructure. By January 2005, up to 10% of telephone subscribers in Japan and South Korea had switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing." The technology has spawned a new industry comprising many VoIP companies that offer services to consumers and businesses . The reported global VoIP market in October 2021

201-446: A guard tone may be employed to prevent this. In voice over IP (VoIP), DTMF signals are transmitted in-band by two methods. When transmitted as audio tones in the voice stream, voice encoding must use a lossless coder, such as μ-law or A-law pulse-code modulation , to preserve the integrity of frequency signals. Still, this method proved often unreliable and was subject to interference from other audio sources. The standard method

268-513: A modem . In-band signaling is insecure because it exposes control signals, protocols and management systems to end users , which may result in falsing . In the 1960s and 1970s, so-called phone phreaks used blue boxes for deliberate falsing, in which the appropriate tones for routing were intentionally generated, enabling the caller to abuse functions intended for testing and administrative use and to make free long-distance calls. Modems may also interfere with in-band signaling, in which case

335-412: 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

402-483: A subscriber , who had to arrange for a telegraph contractor to construct a line between them, for example, between a home and a shop. Users who wanted the ability to speak to several different locations would need to obtain and set up three or four pairs of telephones. Western Union , already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco , and Bell

469-437: A water microphone , some had a metal diaphragm that induced current in an electromagnet wound around a permanent magnet, and some were dynamic – their diaphragm vibrated a coil of wire in the field of a permanent magnet or the coil vibrated the diaphragm. The sound-powered dynamic variants survived in small numbers through the 20th century in military and maritime applications, where its ability to create its own electrical power

536-479: A DC transformer which plugs into a wall AC power outlet. A mobile phone or cellphone or hand phone is a handheld telephone which connects via radio transmissions to a cellular telephone network . The cellular network consists of a network of ground based transmitter/receiver stations with antennas – which are usually located on towers or on buildings – and infrastructure connecting to land-based telephone lines. Analog cellular networks first appeared in 1979, with

603-470: A commercial break. The network blamed "a brief equipment failure." NBC reported that no commercial advertising was lost. Prior to Super Bowl XLV , Green Bay, Wisconsin , radio station WCHK-FM announced that it would intentionally go to dead air during the game, since the hometown Packers were playing in the game and station management believed nobody would be listening to music while the Super Bowl

670-439: A computer softphone application, utilizing the microphone and headset devices of a personal computer or smartphone. While traditional analog telephones are typically powered from the central office through the telephone line, digital telephones require a local power supply. Internet-based digital service also requires special provisions to provide the service location to the emergency services when an emergency telephone number

737-413: A display for caller ID . In addition, answering machine function may be built in. The cordless handset contains a rechargeable battery , which the base station recharges when the handset rests in its cradle. Muilt-handset systems generally also have additional charging stands. A cordless telephone typically requires a constant electricity supply to power the base station and charger units by means of

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804-430: A dynamic transmitter or by the powering of a transmitter with a local battery. One of the jobs of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century, telephones powered from the telephone exchange over the same wires that carried the voice signals became common. Early telephones used a single wire for the subscriber's line, with ground return used to complete

871-642: A few seconds. In the U.S., prolonged dead air, such as a shutdown occurring without permission, is an actionable offense that can result in fines from the Federal Communications Commission (FCC). According to the FCC, a station has a 30-day limit for going silent without approval. On September 11, 1987, Dan Rather walked off the set of the CBS Evening News when a late running U.S. Open tennis match threatened to delay

938-417: A handle with the receiver and transmitter attached, now called a handset , separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular. Disadvantages of single-wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and, for long-distance telephones, four-wire circuits . Users at

1005-486: A loop of music. The playlist is fixed so staff listening in to their own station can recognize the pattern of titles, infer how long the outage has already (at least) lasted and take action to fix the problem. Apart from providing a safeguard in the event of unscheduled interruption (like a fire in the building or technical issues), this mechanism may be used deliberately during programmed blackouts caused by strikes of technicians, journalists, and producers. When staff of

1072-591: A satellite phone is that it can be used in such regions where local terrestrial communication infrastructures, such as landline and cellular networks, are not available. Satellite phones are popular on expeditions into remote locations, hunting, fishing, maritime sector, humanitarian missions, business trips, and mining in hard-to-reach areas, where there is no reliable cellular service. Satellite telephones rarely get disrupted by natural disasters on Earth or human actions such as war, so they have proven to be dependable communication tools in emergency situations, when

1139-404: A short distance from the base station. Base stations include a radio transceiver which enables full-duplex, outgoing and incoming signals and speech with the handsets. The base station often includes a microphone, audio amplifier , and a loudspeaker to enable hands-free speakerphone conversations, without needing to use a handset. The base station may also have a numeric keypad for dialing, and

1206-429: A single molded plastic handle, which when not in use was secured in a cradle in the base unit. The circuit diagram of the model 202 shows the direct connection of the transmitter to the line, while the receiver was inductively coupled. In local battery configurations, when the local loop was too long to provide sufficient current from the exchange, the transmitter was powered by a local battery and inductively coupled, while

1273-428: A telephone are a microphone ( transmitter ) to speak into and an earphone ( receiver ) which reproduces the voice at a distant location. The receiver and transmitter are usually built into a handset which is held up to the ear and mouth during conversation. The transmitter converts the sound waves to electrical signals which are sent through the telecommunications system to the receiving telephone, which converts

1340-514: A wired interface, such as USB or Lightning connectors. Smartphones, being able to run apps , have vastly expanded functionality compared to previous mobile phones. Having internet access and built in cameras, smartphones have made video calling readily accessible via IP connections. Smartphones also have access to a large number of web services and web apps, giving them functionality similar to traditional computers, although smartphones are often limited by their relatively small screen size and

1407-400: Is called. A cordless telephone or portable telephone consists of a base station unit and one or more portable cordless handsets . The base station connects to a telephone line, or provides service by voice over IP (VOIP). The handset communicates with the base station via radio frequency signals. A handset's operational range is limited, usually to within the same building or within

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1474-580: Is considered one of the worst things that can occur. Moreover, dead air may impact advertising revenue if it affects the airplay of paid commercials. The term "dead air" does not refer to a broadcast transmitter that is intentionally shut down, i.e. "closed", " signed off " or " off the air ", by a control operator. Such a broadcast transmitter is said to have gone " dark ". Broadcast stations can use programmable devices known as "silence sensors", "off air alarms" or "silence monitors" that will sound an alarm and alert personnel if dead air persists more than

1541-529: Is derived from Ancient Greek : τῆλε , romanized :  tēle , lit.   'far' and φωνή ( phōnē , voice ), together meaning distant voice . In 1876, Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice at a second device. This instrument was further developed by many others, and became rapidly indispensable in business , government , and in households . The essential elements of

1608-443: Is desired, is usually done by escaping the control instructions. Occasionally, however, networks are designed so that data is, to a varying degree, garbled by the signaling. Allowing data to become garbled is usually acceptable when transmitting sounds between humans, since the users rarely notice the slight degradation, but this leads to problems when sending data that has very low error tolerance, such as information transmitted using

1675-606: Is the address of the call recipient's telephone in the telecommunications system, but other methods existed in the early history of the telephone. The first telephones were directly connected to each other from one customer's office or residence to another customer's location. Being impractical beyond just a few customers, these systems were quickly replaced by manually operated centrally located switchboards . These exchanges were soon connected together, eventually forming an automated, worldwide public switched telephone network . For greater mobility, various radio systems were developed in

1742-575: Is to digitally remove DTMF tones from the audio at the source and from the Real-time Transport Protocol (RTP) voice stream and encode them separately as a digital information payload, often termed named telephone events (NTE), according to RFC 4733. Such DTMF frames are transmit in-band with all other RTP packets on the identical network path. In contrast to in-band transmission of DTMF, VoIP signaling protocols also implement out-of-band method of DTMF transmission. For example,

1809-663: The Earth instead of terrestrial cell sites , as cellphones do. Therefore, they can work in most geographic locations on the Earth's surface, as long as open sky and the line-of-sight between the phone and the satellite is provided. Depending on the architecture of a particular system, coverage may include the entire Earth or only specific regions. Satellite phones provide similar functionality to terrestrial mobile telephones; voice calling , text messaging , and low-bandwidth Internet access are supported through most systems. The advantage of

1876-572: The Reis telephone , in c. 1860. His device appears to be the first device based on the conversion of sound into electrical impulses. The term telephone was adopted into the vocabulary of many languages. It is derived from the Greek : τῆλε , tēle , "far" and φωνή, phōnē , "voice", together meaning "distant voice". Credit for the invention of the electric telephone is frequently disputed. As with other influential inventions such as radio , television ,

1943-590: The Session Initiation Protocol (SIP), as well as the Media Gateway Control Protocol (MGCP) define special message types for the transmission of digits. As a method of in-band signaling, DTMF tones were also used by cable television broadcasters to indicate the start and stop times of local insertion points during station breaks for the benefit of cable companies. Until better, out-of-band signaling equipment

2010-426: The light bulb , and the computer , several inventors pioneered experimental work on voice transmission over a wire and improved on each other's ideas. New controversies over the issue still arise from time to time. Charles Bourseul , Antonio Meucci , Johann Philipp Reis , Alexander Graham Bell , and Elisha Gray , amongst others, have all been credited with the invention of the telephone. Alexander Graham Bell

2077-483: The model 500 telephone in the United States, were developed that permitted larger local networks centered around central offices. A breakthrough new technology was the introduction of Touch-Tone signaling using push-button telephones by American Telephone & Telegraph Company (AT&T) in 1963. The invention of the transistor in 1947 dramatically changed the technology used in telephone systems and in

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2144-447: The smartphone , the dominant type of telephone in the world today. Before the development of the electric telephone, the term telephone was applied to other inventions, and not all early researchers of the electrical device used the term. Perhaps the earliest use of the word for a communications system was the telephon created by Gottfried Huth in 1796. Huth proposed an alternative to the optical telegraph of Claude Chappe in which

2211-658: The 1990s, mobile phones have gained other features which are not directly related to their primary function as telephones. These include text messaging, calendars, alarm clocks, personal schedulers, cameras, music players, games and later, internet access and smartphone functionality. Nearly all mobile phones have the ability to send text messages to other users via the SMS (Short Message Service) protocol. The multimedia messaging service (MMS) protocol enables users to send and receive multimedia content, such as photos, audio files and video files. As their functionality has increased over

2278-493: The advent of smartphones, mobile phone manufacturers have also included consumer electronics companies, such as Apple , Samsung and Xiaomi . As of 2022, most mobile phones are smartphones, being a combination of a mobile phone and a personal computing device in the same unit. Most smartphones are primarily operated using a graphical user interface and a touch screen. Many phones have a secondary voice user interface, such as Siri on Apple iPhones , which can operate many of

2345-481: The audio of the telephone call. In-band signaling is also used on older telephone carrier systems to provide inter-exchange information for routing calls. Examples of this kind of in-band signaling system are the Signaling System No. 5 (SS5) and its predecessors, and R2 signalling . Separating the control signals, also referred to as the control plane, from the data, if a bit-transparent connection

2412-426: The beginning of the 20th century did not place long-distance calls from their own telephones but made an appointment and were connected with the assistance of a telephone operator. What turned out to be the most popular and longest-lasting physical style of telephone was introduced in the early 20th century, including Bell's 202-type desk set. A carbon granule transmitter and electromagnetic receiver were united in

2479-513: The bell coil to allow the AC ringer signal through while still blocking DC (keeping the phone " on hook "). Telephones connected to the earliest Strowger switch automatic exchanges had seven wires, one for the knife switch , one for each telegraph key , one for the bell, one for the push-button and two for speaking. Large wall telephones in the early 20th century usually incorporated the bell, and separate bell boxes for desk phones dwindled away in

2546-583: The cable industry was discontinued because it was distracting to viewers, and was susceptible to interference when DTMF tones were sounded by characters in television shows. For example, a character dialing a Touch-Tone telephone in a television show could cause the cable company computers to switch away from a "hot feed" to dead air , and the cost of human-imperceptible signaling technologies decreased. In-band signaling applies only to channel-associated signaling (CAS). In common channel signaling (CCS) separate channels are used for control and data, as opposed to

2613-439: The circuit (as used in telegraphs ). The earliest dynamic telephones also had only one port opening for sound, with the user alternately listening and speaking (or rather, shouting) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but also more expensive. At first, the benefits of a telephone exchange were not exploited. Instead, telephones were leased in pairs to

2680-420: The device's functions, as well as enabling users to use spoken commands to interact with the internet. Typically alphanumeric text input is accomplished via an on-screen virtual keyboard, although some smartphones have a small physical keyboard. Smartphones offer the ability to access internet data through the cellular network and via wi-fi, and usually allow direct connectivity to other devices via Bluetooth or

2747-487: The feeds should be switched to and away from the master control feed, to locally-broadcast commercials. The following is an example of such a sequence by a cable company that communicated the following to the cable company's broadcast equipment: SWITCH TO LOCAL NOW - SWITCH TO LOCAL NOW - PREPARE TO SWITCH BACK - PREPARE TO SWITCH BACK - SWITCH BACK TO NATIONAL NOW - SWITCH BACK TO NATIONAL NOW - "IF YOU HAVEN'T SWITCHED BACK TO NATIONAL NOW, DO SO IMMEDIATELY" DTMF signaling in

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2814-524: The first digital cellular networks appearing in the early 1990s. Mobile phones require a SIM card to be inserted into the phone. The SIM card is a small PVC card containing a small integrated circuit which stores the user's international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers to the cellular network. Mobile phones generally incorporate an LCD or OLED display, with some types, such as smartphones, having touch screens. Since

2881-430: The handset was on the cradle. In the 1930s, telephone sets were developed that combined the bell and induction coil with the desk set, obviating a separate ringer box. The rotary dial becoming commonplace in the 1930s in many areas enabled customer-dialed service, but some magneto systems remained even into the 1960s. After World War II, the telephone networks saw rapid expansion and more efficient telephone sets, such as

2948-426: The local communications system can be compromised. Dead air Dead air , also known as unmodulated carrier , is an unintended period of silence that interrupts a broadcast during which no audio or video program material is transmitted. Dead air occurs in radio broadcasting when no audio program is transmitted for an extended period of time, usually more than a few seconds. In television broadcasting ,

3015-428: The long-distance transmission networks, over the next several decades. With the development of stored program control and MOS integrated circuits for electronic switching systems , and new transmission technologies such as pulse-code modulation (PCM), telephony gradually evolved towards digital telephony , which improved the capacity, quality, and cost of the network. Integrated Services Digital Network (ISDN)

3082-433: The mid-20th century for transmission between mobile stations on ships and in automobiles. Hand-held mobile phones were introduced for personal service starting in 1973. In later decades, the analog cellular system evolved into digital networks with greater capability and lower cost. Convergence in communication services has provided a broad spectrum of capabilities in cell phones, including mobile computing, giving rise to

3149-435: The middle of the century. Rural and other telephones that were not on a common battery exchange had a magneto hand-cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the operator. Some local farming communities that were not connected to the main networks set up barbed wire telephone lines that exploited the existing system of field fences to transmit

3216-495: The operators in the signaling towers would shout to each other by means of what he called "speaking tubes", but would now be called giant megaphones . A communication device for sailing vessels, called telephone , was invented by Captain John Taylor in 1844. This instrument used four air horns to communicate with vessels in foggy weather. Johann Philipp Reis used the term in reference to his invention, commonly known as

3283-409: The receiver was included in the local loop. The coupling transformer and the ringer were mounted in a separate enclosure, called the subscriber set. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line one to ten times for each digit, and the hook switch (in the center of the circuit diagram) disconnected the line and the transmitter battery while

3350-559: The shared channel in CAS, so all control is out-of-band by definition. In computer data, the term refers to embedding any kind of metadata directly within regular data. These uses have similar tradeoffs as in telecommunications, such as opening an attack surface vs. simplifying processing. A few of many examples: When out-of-band communication is unavailable, one of two techniques may be used to preserve network transparency . Telephone A telephone , colloquially referred to as

3417-403: The signal. In the 1890s a new smaller style of telephone was introduced, packaged in three parts. The transmitter stood on a stand, known as a " candlestick " for its shape. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook". Previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user

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3484-406: The signals into audible sound in the receiver or sometimes a loudspeaker . Telephones permit transmission in both directions simultaneously. Most telephones also contain an alerting feature, such as a ringer or a visual indicator, to announce an incoming telephone call. Telephone calls are initiated most commonly with a keypad or dial, affixed to the telephone, to enter a telephone number , which

3551-510: The size of their keyboards. Typically, smartphones feature such tools as cameras, media players, web browsers, email clients, interactive maps, satellite navigation and a variety of sensors, such as a compass , accelerometers and GPS receivers . In addition to voice calls, smartphone users commonly communicate using a wide variety of messaging formats, including SMS, MMS, email, and various proprietary messaging services, such as iMessage and various social media platforms. In 2002, only 10% of

3618-449: The start of his news broadcast. The match then ended sooner than expected but Rather was gone. The network broadcast six minutes of dead air before Rather was found and returned to the studio. CBS affiliates criticized Rather for the incident. One significant case of dead air occurred during Super Bowl LII in 2018, when the NBC television broadcast experienced 26 seconds of dead air during

3685-517: The telephone switch, which allowed for the formation of telephone exchanges , and eventually networks. In the United Kingdom, the blower is used as a slang term for a telephone. The term came from navy slang for a speaking tube . In the U.S., a somewhat dated slang term refers to the telephone as "the horn," as in "I couldn't get him on the horn," or "I'll be off the horn in a moment." Early telephones were technically diverse. Some used

3752-408: The telephone to work a fluctuating current reproduced sounds the best. The fluctuating currents became the basis for the working telephone, creating Bell's patent. That first patent by Bell was the master patent of the telephone, from which other patents for electric telephone devices and features flowed. In 1876, shortly after Bell's patent application, Hungarian engineer Tivadar Puskás proposed

3819-565: The term denotes the absence of both audio and video program material. However, a carrier wave is still transmitting. In radio, the result is silence, and in television, the result is a silent black or gray screen. Television directors may use the command "fade to black" or "to black" to indicate a momentary transition to a completely black image. However, the term "dead air" is most often used in cases where program material comes to an unexpected halt, either through operator error or technical malfunction. Among professional broadcasters, dead air

3886-456: The world's population used mobile phones and by 2005 that percentage had risen to 46%. By the end of 2009, there were a total of nearly 6 billion mobile and fixed-line telephone subscribers worldwide. This included 1.26 billion fixed-line subscribers and 4.6 billion mobile subscribers. A satellite telephone, or satphone, is a type of mobile phone that connects to other phones or the telephone network by radio link through satellites orbiting

3953-517: The years, many types of mobile phone, notably smartphones, require an operating system to run. Popular mobile phone operating systems in the past have included Symbian , Palm OS , BlackBerry OS and mobile phone versions of Windows . As of 2022, the most used operating systems are Google's Android and Apple's iOS . Before the era of smartphones, mobile phones were generally manufactured by companies specializing in telecommunications equipment, such as Nokia , Motorola , and Ericsson . Since

4020-481: Was $ 85.2 billion with a projection of $ 102.5 billion by 2026. IP telephony uses high-bandwidth Internet connections and specialized customer premises equipment to transmit telephone calls via the Internet, or any modern private data network. The customer equipment may be an analog telephone adapter (ATA) which translates the signals of a conventional analog telephone; an IP Phone , a dedicated standalone device; or

4087-449: Was being broadcast on another station. Many broadcasters install a silence detector independently operating from their broadcasting headquarters. In the event of dead air lasting more than an acceptable duration, e.g. ≤ −70 dB and (if applicable) static/no picture for 30 seconds, an emergency program is cued. The emergency program contains at least some generic audio (and video) with a station identification . Radio stations usually play

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4154-570: Was crucial. Most, however, used the Edison/Berliner carbon transmitter , which was much louder than the other kinds, even though it required an induction coil which was an impedance matching transformer to make it compatible with the impedance of the line. The Edison patents kept the Bell monopoly viable into the 20th century, by which time the network was more important than the instrument. Early telephones were locally powered, using either

4221-401: Was developed in the 1990s, fast, unacknowledged, and loud DTMF tone sequences could be heard during the commercial breaks of cable channels in the United States and elsewhere. These DTMF sequences were sent by the originating cable network's equipment at the uplink satellite facility, and were decoded by equipment at local cable companies. A specific tone sequence indicated the exact time that

4288-521: Was launched in the 1980's, providing businesses and consumers with access to digital telephony services such as data, voice, video , and fax services. The development of digital data communications methods made it possible to digitize voice and transmit it as real-time data across computer networks and the Internet , giving rise to the field of Internet Protocol (IP) telephony, also known as voice over Internet Protocol (VoIP). VoIP has proven to be

4355-406: Was less likely to leave the phone "off the hook". In phones connected to magneto exchanges, the bell, induction coil, battery and magneto were in a separate bell box or " ringer box ". In phones connected to common battery exchanges, the ringer box was installed under a desk, or other out-of-the-way place, since it did not need a battery or magneto. Cradle designs were also used at this time, having

4422-407: Was not slow in appreciating the potential. Signalling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator , by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell in a ringer box , first operated over a second wire, and later over the same wire, but with a condenser ( capacitor ) in series with

4489-550: Was the first to be awarded a patent for the electric telephone by the United States Patent and Trademark Office (USPTO) in March 1876. Before Bell's patent, the telephone transmitted sound in a way that was similar to the telegraph. This method used vibrations and circuits to send electrical pulses, but was missing key features. Bell found that this method produced a sound through intermittent currents, but in order for

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