A videophone is a telephone with a video screen, and is capable of full duplex (bi-directional) video and audio transmissions for communication between people in real-time. It was the first form of videotelephony, later to be followed by videoconferencing, webcams, and finally telepresence.
At the dawn of the technology, videotelephony also included image phones which would exchange still images between units every few seconds over conventional POTS-type telephone lines, essentially the same as slow scan TV systems.
Currently videophones are particularly useful to the deaf and speech-impaired who can use them with sign language, and also with video relay services to communicate with hearing persons. Videophones are also highly useful to those with mobility issues or those who are located in distant places and are in need of telemedical or tele-educational services.
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The name 'videophone' never became as standardized as its earlier counterpart 'telephone', resulting in a variety of names and terms being used worldwide, and even within the same region or country. Videophones are also known as 'video phones', 'videotelephones' (or 'video telephones') and often by an early trademarked name Picturephone, which was the world's first commercial videophone produced in volume. The compound name 'videophone' slowly entered into general use after 1950,[1] although 'video telephone' likely entered the lexicon earlier after video was coined in 1935.[2]
Videophone calls (also: videocalls and video chat),[3] differ from videoconferencing in that they expect to serve individuals, not groups.[4] However that distinction has become increasingly blurred with technology improvements such as increased bandwidth and sophisticated software clients that can allow for multiple parties on a call. In general everyday usage the term videoconferencing is now frequently used instead of videocall for point-to-point calls between two units. Both videophone calls and videoconferencing are also now commonly referred to as a video link.
Webcams are popular, relatively low cost devices which can provide live video and audio streams via personal computers, and can be used with many software clients for both video calls and videoconferencing.[5]
A videoconference system is generally higher cost than a videophone and deploys greater capabilities. A videoconference (also known as a videoteleconference) allows two or more locations to communicate via live, simultaneous two-way video and audio transmissions. This is often accomplished by the use of a multipoint control unit (a centralized distribution and call management system) or by a similar non-centralized multipoint capability embedded in each videoconferencing unit. Again, technology improvements have circumvented traditional definitions by allowing multiple party videoconferencing via web-based applications.[6][7] A separate webpage article is devoted to videoconferencing.
A telepresence system is a high-end videoconferencing system and service usually employed by enterprise-level corporate offices. Telepresence conference rooms use state-of-the art room designs, video cameras, displays, sound-systems and processors, coupled with high-to-very-high capacity bandwidth transmissions.
Typical uses of the various technologies described above include videocalling or videoconferencing on a one-to-one, one-to-many or many-to-many basis for personal, business, educational, deaf Video Relay Service and tele-medical, diagnostic and rehabilitative use or services. New services utilizing videocalling and videoconferencing, such as personal videocalls to inmates incarcerated in penitentiaries, and videoconferencing to resolve airline engineering issues at maintenance facilities, are being created or evolving on an on-going basis.
Other names for videophone that have been used in English are: Viewphone (the British Telecom equivalent to AT&T's Picturephone),[8] and visiophone, a common French translation that has also crept into limited English usage, as well as over twenty less common names and expressions. Latin-based translations of videophone in other languages include vidéophone (French), bildtelefon (German), videotelefono (Italian), both videófono and videoteléfono (Spanish), both beeldtelefoon and videofoon (Dutch), and videofonía (Catalan).
Barely two years after the telephone was first patented in the United States in 1876 by Alexander Graham Bell, an early concept of a combined videophone and wide-screen television called a telephonoscope was conceptualized in the popular periodicals of the day. It was also mentioned in various early science fiction works such as Le Vingtième siècle: La vie électrique (the 20th century: the electrical life) and other works written by Albert Robida, and was also sketched in various cartoons by George du Maurier as a fictional invention of Thomas Edision. One such sketch was published on December 9, 1878 in Punch Magazine.[9][10][11]
The term 'telectroscope' was also used in 1878 by French writer and publisher Louis Figuier, to popularize an invention wrongly interpreted as real and incorrectly ascribed to Dr. Alexander Graham Bell.[12] Written under the pseudonym "Electrician", his article claimed that "an eminent scientist" had invented a device whereby objects or people anywhere in the world "....could be seen anywhere by anybody". The device, among other functions, would allow merchants to transmit pictures of their wares to their customers, and the contents of museum collections to be made available to scholars in distant cities.[13] In the era prior to the advent of broadcasting, electrical "seeing" devices were conceived as adjuncts to the telephone, thus creating the concept of a videophone.[14][15]
Fraudulent reports of 'amazing' advances in video telephones would be publicized as early as 1880 and would reoccur every few years, such as the episode of 'Dr. Sylvestre' of Paris who claimed to have invented a powerful (and inexpensive) video telephone, termed a 'spectograph', in 1902, the intellectual property rights to which he believed were worth $5,000,000. After reviewing information on his claim, Dr. Bell denounced the supposed invention as a "fairy tale", and publicly commented on the charlatans who were promoting bogus videophone inventions for financial gain or self-promotion.[16][17]
In April 1891, Dr. Alexander Graham Bell did actually record conceptual notes on an 'electrical radiophone', which discussed "....the possibility of seeing by electricity" using devices that employed tellurium or selenium imaging components.[18] Bell wrote, decades prior to the invention of the image dissector:[18]
Should it be found ... [that the image sensor] is illuminated, then an apparatus might be constructed in which each piece of selenium is a mere speck, like the head of a small pin, the smaller the better. The darkened selenium should be placed in a cup-like receiver which can fit over the eye ... Then, when the first selenium speck is presented to an illuminated object, it may be possible that the eye in the darkened receiver, should perceive, not merely light, but an image of the object ...
Bell went on to later predict that: "...the day would come when the man at the telephone would be able to see the distant person to whom he was speaking."[19][20] The discoveries in physics, chemistry and material sciences underlying video technology would not be in place until the mid-1920s, first being utilized in electromechanical television. More practical 'all-electronic' video and television would not emerge until 1939, but would then suffer several more years of delays due to World War II.
The compound name 'videophone' slowly entered into general usage after 1950,[1] although 'video telephone' likely entered the lexicon earlier after video was coined in 1935.[2] Prior to that time there appeared to be no standard terms for 'video telephone', with expressions such as 'sight-sound television system', 'visual radio' and nearly 20 others (in English) being used to describe the marriage of telegraph, telephone, television and radio technologies employed in early experiments.[21][22][23]
Among the technological precursors to the videophone were telegraphic image transmitters created by several companies, such as the wirephoto used by Western Union, and the teleostereograph developed by AT&T's Bell Labs,[24] which were forerunners of today's fax (facsimile) machines. Such early image transmitters were themselves based on previous work by Ernest Hummel and others in the 19th century. By 1927 AT&T had created its earliest electromechanical television-videophone called the ikonophone (from Greek: 'image-sound'),[25] which operated at 18 frames per second and occupied half a room full of equipment cabinets.[26][27] An early U.S. test in 1927 had their then-Commerce Secretary Herbert Hoover address an audience in New York City from Washington, D.C.; although the audio portion was two-way, the video portion was one-way with only those in New York being able to see Hoover.
By 1930, AT&T's 'two-way television-telephone' system was in experimental use.[14][23] The Bell Labs' Manhattan facility devoted years of research to it during the 1930s, led by Dr. Herbert Ives along with his team of more than 200 scientists, engineers and technicians, intending to develop it for both telecommunication and broadcast entertainment purposes.[28][15] After the Second World War, Bell Labs' efforts would be resumed in the 1950s and 1960s, eventually leading to AT&T's Picturephone.
In early 1936 the world's first public video telephone service was developed by Dr. Georg Schubert and opened by the German Reichspost (Post Office) between Berlin and Leipzig, utilizing broadband coaxial cable to cover the distance of approximately 100 miles (160 km). The system employed mechanical television scanning and 8 inches (20 cm) square displays with a resolution of 180 lines operating at 25 frames per second.[29] Its opening was inaugurated by the Minister of Posts Paul von Eltz-Rübenach in Berlin on March 1, 1936, who viewed and spoke with Leipzig's chief burgomaster.[30][31] The same coaxial cables were also used to distribute television programming throughout Germany.
In the initial service trial, broadband coaxial cable lines initially linked Berlin to Leipzig. After a period of experimentation the system entered public use and was soon extended 100 miles (160 km) from Berlin to Hamburg, and in July 1938 from Leipzig to Nuremberg and Munich, eventually providing more than 620 miles (1,000 km) of transmission lines. The videophones were integrated within large public telephone booths, with two booths provided per city. Calls between Berlin and Leipzig cost RM3½, approximately one sixth of a British pound sterling, or about one-fifteenth of the average weekly wage.[29] The video telephone equipment in Berlin was designed and built by the German Post Office Laboratory. Devices used in other German cities were developed by Fernseh-Aktiengesellschaft, which was partly owned by the Baird Television Ltd. of the U.K.,[29] inventors of the world's first working television. While the system's image quality was primitive by modern standards, it was deemed impressive in contemporary reports of the era, with users able to clearly discern the hands on wristwatches.[29]
The special public videotelephone service was offered to the general public, which had to simultaneously visit special post office videophone booths in their respective cities, but which at the same time also had Nazi political and propagandistic overtones similar to the broadcasting of the 1936 Olympic Games in Berlin.[32] The German Post Office announced ambitious plans to extend their public video telephone network to Cologne, Frankfurt and Vienna, Austria, but expansion plans were discontinued in 1939 with the start of the Second World War.[33][34] The German public videophone system was subsequently closed in 1940.[35]
The Deutsche Bundespost postal service would later develop and deploy its BIGFON (Broadband Integrated Glass-Fiber Optical Network) videotelephony network from 1981 to 1988, serving several large German cities, and also created one of Europe's first public switched broadband services in 1989.[36]
In the United States AT&T's Bell Labs conducted extensive research and development of videophones, eventually leading to public demonstrations of its trademarked Picturephone product and service in the 1960s, including displays at the 1964 New York World's Fair.[37] The first 'Mod I' demonstration units used small oval housings on swivel stands, intended to stand on desks. Similar AT&T Picturephone units were also featured at the Telephone Pavilion (also called the "Bell Telephone Pavilion") at Expo 67, an International World's Fair held in Montreal, Canada in 1967.[37][38][39] Demonstration units were available at the fairs for the public to test, with fair-goers permitted to make videophone calls to volunteer recipients at other locations.
The United States would not see its first public video telephone booths until 1964, when AT&T installed their earliest commercial videophone unit, the Picturephone Mod I, in public booths in three cities: New York, Washington, D.C. and Chicago.[26] Picturephone booths were set up in New York's Grand Central Terminal and elsewhere. Picturephones were also installed in the offices of Westinghouse in Pittsburgh, and in other technology companies. However the use of reservation time slots and their initial cost of US$16 (approximately $113 in current dollars[40]) per three minute call at public booths greatly limited their appeal resulting in their closure by 1968.[19][26]
Unrelated difficulties at New York Telephone also slowed AT&T's efforts, and few customers signed up for the service in either city. At its peak Picturephone service had only about 500 subscribers, with the service fading away in the 1970s. AT&T's initial Mod I and its upgraded Picturephone Mod II programs,, researched principally at its Bell Labs, spanned 15 years and consumed more than US$500 million, eventually meeting with commercial failure.[41] AT&T concluded that its early videophone was a "concept looking for a market" and discontinued its Picturephone service in the late 1970s.[41] The research and development programs conducted by Bell Labs were nonetheless highly notable for the beyond-the-state-of-the-art results produced in materials science, advanced telecommunications, microelectronics and information technologies.
Color on AT&T's Picturephone was not employed with their early models. These Picturephone units packaged Plumbicon cameras and small CRT displays within their housings. The cameras were located atop their screens to help users see eye to eye. See this section for more information on Picturephone technology. Later generation display screens were larger than in the original demonstration units, approximately six inches (15 cm) square in a roughly cubical cabinet.
AT&T would then market its VideoPhone 2500 to the general public from 1992 to 1995 with prices starting at US$1,500 and later dropping to $1,000.[42] The VideoPhone was designed to provide low-frame rate compressed color video on ordinary Plain Old Telephone Service (POTS) telephone lines, circumventing high cost ADSL telephone service. Again, the company met with very little commercial success.
Beginning in the late 1960s, several countries worldwide sought to compete with AT&T's advanced development of their Picturephone in the United States. However such projects were research and capital intensive, and fraught with difficulties in being deployed commercially.
In Sweden electronics maker Ericsson began developing one in the mid-1960s, intending to market them to government, institutions, businesses and industry, but not to consumers due to AT&T's lack of success in that market segment. Tests were conducted in Stockholm, including trial communications in banking in Stockholm. Ultimately Ericsson chose not to proceed with production.[43]
In France, the defense and electronics manufacturer Matra was one of three French companies that sought to develop videophones in the early 1970s, spurred by the Picturephone in the United States. Initial plans by Matra included the deployment of 25 units to France's Centre national d'études des télécommunications (CNET of France Télécom) for their internal use in 1972. CNET intended to guide its initial use towards the business sector, to be later followed by personal home usage. Its estimated unit cost in 1971 was the equivalent of £325, with a monthly usage subscription charge of £3.35.[44]
Studies of applications of videotelephony were conducted by CNET in France in 1972, with its first commercial applications for videophones appearing in 1984. The delay was due to the problem of insufficient bandwidth, with 2 Mb per second being required for transmitting both video and audio signals. The problem was solved worldwide by the creation of software for data encoding and compression via video coding and decoding algorithms, also known as codecs.
In Japan the Lumaphone was developed and marketed by Mitsubishi in 1985. The project was originally started by the Ataritel division of the Atari Video Game Company in 1983 under the direction of Atari's Steve Bristow. Atari then sold its division to Mitsubishi in 1984. The Lumaphone was marketed by Mitsubishi Electric of America in 1986 as the Luma LU-1000. Similar to Bell Labs' very early image transfer phone of 1956, it could transmit still images every 3–5 seconds over analog POTS lines, and could also be connected to a regular TV or monitor for improved teleconferencing. A larger video image was available by attaching its optional VisiTel LU-500 display.[45][46]
In the United States, the Intellect was a neo- or prototype wireless videophone, developed in 1993 by inventor Daniel A. Henderson, and which featured still image and non-live video clip transfers.[47][48] The pioneering system and device were designed to receive pictures and video data sent from an originator to a message center for transmission and display to a wireless device such as a cellular telephone.[49][50]
The Intellect was essentially a cell phone handset with a large black and white display that could show still images and video clips downloaded remotely from a computer via a wireless transmitter. The data transfer protocols pioneered in the Intellect design were later deployed with the common camera phones released in the early 2000s.[48] However, the complete integration of the cellular phone, digital camera and its wireless transmission infrastructure would take a few more years to complete. The prototype models were donated to the Smithsonian's National Museum of American History in 2007.[51][52]
Early AT&T Picturephones had few users, in part because the service was relatively expensive, with a service cost of approximately US$90 per month in 1974. However as modern technology reduced videotelephony costs to nominal, at least in the case of webcams, videophone calling continued to be only marginally utilized. This contrasts to many early, overly optimistic views that videotelephony would become ubiquitous.
There are several other reasons why videotelephony remains a peripheral telecommunications technology. One of the most important may be psychological: just as many people choose to listen to radio instead of watching television, individuals can prefer regular telephone conversations over videophone calls. This reason for poor acceptance may reflect that people can actually desire less fidelity in their communications. Additionally, others did not want to be seen at home—where a videophone can be viewed as too intrusive into one's private life. The reasoning and psychology can be summed as, although its true that "one picture can say a thousand words", its also true that, in poor situations, "one picture can say a thousand negative words".
Another reason may be that videophone calling can be a poor analog for direct face-to-face conversation. Videophone users commonly look at the video screen and not at the video camera, preventing users from having direct eye-to-eye contact, as the video cameras are usually positioned away from the screen. The issue of poor eye contact has been addressed on the more sophisticated videophone and videoconferencing systems (as far back as the 1960s) by means of cameras hidden behind translucent display screens, directly inline with the projected image of the person being spoken to.
However it's also been observed that videotelephony is of great benefit to certain groups and demographics, such as members of families living far apart and who may have a strong desire, but little opportunity for face-to-face contact. Other groups that have embraced videotelephony include those in the deaf community where high quality video greatly facilitates sign language communications both within and outside of their personal and social settings.[53] The elderly and those who are physically immobile also benefit from video telecommunications.
The widest deployment of video telephony now occurs in mobile phones, as nearly all mobile phones supporting UMTS networks can work as videophones using their internal cameras, and are able to make video calls wirelessly to other UMTS users in the same country or internationally. As of the second quarter of 2007, there are over 131 million UMTS users (and hence potential videophone users), on 134 networks in 59 countries.
Videophones are increasingly used in the provision of telemedicine to the elderly and to those in remote locations, where the ease and convenience of quickly obtaining diagnostic and consultative medical services are readily apparent.[54] In one single instance quoted in 2006: "A nurse-led clinic at Letham has received positive feedback on a trial of a video-link which allowed 60 pensioners to be assessed by medics without travelling to a doctor's office or medical clinic."[54] A further improvement in telemedical services has been the development of new technology incorporated into special videophones to permit remote diagnostic services, such as blood sugar level, blood pressure and vital signs monitoring. Such units are capable of relaying both regular audiovideo plus medical data over either standard (POTS) telephone or newer broadband lines.[55]
Videotelephony has also been deployed in corporate teleconferencing, also available through the use of public access videoconferencing rooms. A higher level of videoconferencing that employs advanced telecommunication technologies and high-resolution displays is called telepresence.
Today the principles, if not the precise mechanisms of a videophone are employed by many users worldwide in the form of webcam videocalls using personal computers, with inexpensive webcams, microphones and free videocalling web client programs. Thus an activity that was disappointing as a separate service has found a niche as a minor feature in software products intended for other purposes.
A videophone can also be created by using an old or inexpensive computer and dedicating it to run as a video softphone. This shows that some users may want to use conventional videophones, but are likely to trade ease of use for lower costs.
Some have argued that unless conventional videophones add considerable value at low cost, and as long as less expensive alternatives (such as webphones) are available, it will be unlikely that dedicated videophones will become popular.
According to Juniper Research, smartphone videophone users will reach 29 million by 2015 globally.[56]
One of the first demonstrations of the ability for telecommunications to help sign language users communicate with each other occurred when AT&T's videophone (trademarked as the "Picturephone") was introduced to the public at the 1964 New York World's Fair –two deaf users were able to communicate freely with each other between the fair and another city.[37] Various other organizations, including British Telecom's Martlesham facility and several universities have also conducted extensive research on signing via videotelephony.[57] The use of sign language via videotelephony was hampered for many years due to the difficulty of its use over slow analogue copper phone lines coupled with the high cost of better quality ISDN (data) phone lines.[57] Those factors largely disappeared with the introduction of more efficient video codecs and the advent of lower cost high-speed ISDN data and IP (Internet) services in the 1990s.
Significant improvements in video call quality of service for the deaf occurred in the United States in 2003 when Sorenson Media Inc. (formerly Sorenson Vision Inc.), a video compression software coding company, developed its VP-100 model stand-alone videophone specifically for the deaf community. It was designed to output its video to the user's television in order to lower the cost of acquisition, and to offer remote control and a powerful video compression codec for unequaled video quality and ease of use with video relay services. Favourable reviews quickly led to its popular usage at educational facilities for the deaf, and from there to the greater deaf community.[58]
Coupled with similar high-quality videophones introduced by other electronics manufacturers, the availability of high speed Internet, and sponsored video relay services authorized by the U.S. Federal Communications Commission in 2002, VRS services for the deaf underwent rapid growth in that country.[58]
Using such video equipment in the present day, the deaf, hard-of-hearing and speech-impaired can communicate between themselves and with hearing individuals using sign language. The United States and several other countries compensate companies to provide 'Video Relay Services' (VRS). Telecommunication equipment can be used to talk to others via a sign language interpreter, who uses a conventional telephone at the same time to communicate with the deaf person's party. Video equipment is also used to do on-site sign language translation via Video Remote Interpreting (VRI). The relative low cost and widespread availability of 3G mobile phone technology with video calling capabilities have given deaf and speech-impaired users a greater ability to communicate with the same ease as others. Some wireless operators have even started free sign language gateways.
Sign language interpretation services via VRS or by VRI are useful in the present-day where one of the parties is deaf, hard-of-hearing or speech-impaired (mute). In such cases the interpretation flow is normally within the same principal language, such as French Sign Language (LSF) to spoken French, Spanish Sign Language (LSE) to spoken Spanish, British Sign Language (BSL) to spoken English, and American Sign Language (ASL) also to spoken English (since BSL and ASL are completely distinct to each other), and so on.
Multilingual sign language interpreters, who can also translate as well across principal languages (such as to and from SSL, to and from spoken English), are also available, albeit less frequently. Such activities involve considerable effort on the part of the translator, since sign languages are distinct natural languages with their own construction, semantics and syntax, different from the aural version of the same principal language.
With video interpreting, sign language interpreters work remotely with live video and audio feeds, so that the interpreter can see the deaf or mute party, and converse with the hearing party, and vice versa. Much like telephone interpreting, video interpreting can be used for situations in which no on-site interpreters are available. However, video interpreting cannot be used for situations in which all parties are speaking via telephone alone. VRS and VRI interpretation requires all parties to have the necessary equipment. Some advanced equipment enables interpreters to control the video camera remotely, in order to zoom in and out or to point the camera toward the party that is signing.
Videophones have historically employed a variety of transmission and reception bandwidths, which can be understood as data transmission speeds. The lower the transmission/reception bandwidth, the lower the data transfer rate, resulting in a more limited and poorer image quality. Data transfer rates and live video image quality are related, but are also subject to other factors such as data compression techniques. Some early videophones employed very low data transmission rates with a resulting sketchy video quality.
Broadband bandwidth is often called "high-speed", because it usually has a high rate of data transmission. In general, any connection of 256 kbit/s (0.256 Mbit/s) or greater is more concisely considered broadband Internet. The International Telecommunication Union Standardization Sector (ITU-T) recommendation I.113 has defined broadband as a transmission capacity at 1.5 to 2 Mbit/s. The United States Federal Communications Commission definition of broadband is 768 kbit/s (0.8 Mbit/s).
Currently, adequate video for some purposes becomes possible at data rates lower than the ITU-T broadband definition, with rates of 768 kbit/s and 384 kbit/s used for some video conferencing applications, and rates as low as 100 kbit per second used for videophones using H.264/MPEG-4 AVC compression protocols. The newer MPEG-4 video and audio compression format can deliver high-quality video at 2 Mbit/s, which is at the low end of cable modem and ADSL broadband performance.
The Picturephone's video bandwidth was 1 MHz with a vertical scan rate of 30 Hz, horizontal scan rate of 8 kHz, and about 250 visible scan lines. The equipment included a Speakerphone hands free telephone, with an added box to control picture transmission. Each Picturephone line used three twisted pairs of ordinary telephone cable, two pairs for video and one for audio and signaling.[59] Cable amplifiers were spaced about a mile apart (1.6 kilometres) with built-in six-band adjustable equalization filters. For distances of more than a few miles, the signal was digitized at 2 MHz and 3 bits per sample DPCM, and transmitted on a T-2 carrier.
The original Picturephone system used contemporary crossbar and multi-frequency operation. Lines and trunks were six wire, one pair each way for video and one pair two way for audio. MF address signaling on the audio pair was supplemented by a Video Supervisory Signal (VSS) looping around on the video quad to ensure continuity. More complex protocols were later adopted for conferencing.
To deploy Picturephone service new wideband crossbar switches were designed and installed into the Bell System's 5XB switch offices, this being the most widespread of the relatively modern kinds. Hundreds of technicians attended schools to learn to operate the Cable Equalizer Test Set and other equipment, and to install Picturephones.
AT&T later marketed the VideoPhone 2500 to the general public from 1992 to 1995. It was limited by analog phone line connection speeds of about 19 Kilobits per second, the video portion being 11,200 bit/s, and with a maximum frame rate of 10 frames per second, but typically much lower. The VideoPhone 2500 used proprietary technology protocols.
Videoconferencing in the late 20th century was limited to the H.323 protocol (notably Cisco's SCCP implementation was an exception), but newer videophones often use SIP, which is often easier to set up in home networking environments. H.323 is still used, but more commonly for business videoconferencing, while SIP is more commonly used in personal consumer videophones. A number of call-setup methods based on instant messaging protocols such as Skype also now provide video. The principal open systems SIP source is Counterpath Corp., which provides support for British Telecom, Deutsche Telekom, Sprint, Telmex, AT&T's Callvantage, and the unified communicator of Cisco and Verizon.
Another protocol used by videophones is H.324, which mixes call setup and video compression. Videophones that work on regular phone lines typically use H.324, but the bandwidth is limited by the modem to around 33 kbit/s, limiting the video quality and frame rate. A slightly modified version of H.324 called 3G-324M defined by 3GPP is also used by some cellphones that allow video calls, typically for use only in UMTS networks.
There is also H.320 standard, which specified technical requirements for narrow-band visual telephone systems and terminal equipment, typically for videoconferencing and videophone services. It applied mostly to dedicated circuit-based switched network (point-to-point) connections of moderate or high bandwidth, such as through the medium-bandwidth ISDN digital phone protocol or a fractionated high bandwidth T1 lines. Modern products based on H.320 standard usually support also H.323 standard.[60]
The IAX2 protocol also supports videophone calls natively, using the protocol's own capabilities to transport alternate media streams.
The Wiktionary entry for videophone Media related to Videophones at Wikimedia Commons