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A videoconference (also known as a videoteleconference) is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously. It has also been called visual collaboration and is a type of groupware. A videoconference in progress using a dedicated device (Aethra) via ISDN and a computer for data interchange support
HistorySimple analog videoconferences could be established as early as the invention of the television. Such videoconferencing systems consisted of two closed-circuit television systems connected via cable. During the first manned space flights, NASA used two radiofrequency (UHF or VHF) links, one in each direction. TV channels routinely use this kind of videoconferencing when reporting from distant locations, for instance. Then mobile links to satellites using special trucks became rather common. Videoconferencing first demonstrated in 1968This technique was very expensive, though, and could not be used for more mundane applications, such as telemedicine, distance education, business meetings, and so on, particularly in long-distance applications. Attempts at using normal telephony networks to transmit slow-scan video, such as the first systems developed by AT&T, failed mostly due to the poor picture quality and the lack of efficient video compression techniques. It was only in the 1980s that digital telephony transmission networks became possible, such as ISDN, assuring a minimum bandwidth (usually 128 kilobits/sec) for compressed video and audio transmission. The first dedicated systems, such as those manufactured by pioneering VTC firms, like PictureTel, started to appear in the market as ISDN networks were expanding throughout the world. Video teleconference systems throughout the 1990's rapidly evolved from highly expensive proprietary equipment, software and network requirements to standards based technology that is readily available to the general public at a reasonable cost. Finally, in the 1990s, IP (Internet Protocol) based videoconferencing became possible, and more efficient video compression technologies were developed, permitting desktop, or personal computer (PC)-based videoconferencing. VTC arrived to the masses and free services and software, such as NetMeeting, MSN Messenger, Yahoo Messenger, and others brought cheap, albeit low-quality, VTC. TechnologyDedicated videoconferencing system with two TV displays, one for the videoconferencing, another for the slide presentation. The VTC console sits on the top of the TV at left and includes a PTZ cameraThe core technology used in a videoteleconference (VTC) system is digital compression of audio and video streams in real time. The hardware or software that performs compression is called a codec (coder/decoder). Compression rates of up to 1:500 can be achieved. The resulting digital stream of 1's and 0's is subdivided into labelled packets, which are then transmitted through a digital network of some kind (usually ISDN or IP). The use of audio modems in the transmission line allow for the use of POTS, or the plain telephony network in some low-speed applications, such as videotelephony, because they convert the digital pulses to/from analog waves in the audio spectrum range. The other components required for a VTC system include:
There are basically two kinds of VTC systems:
Echo cancellationA fundamental feature of professional VTC systems is acoustic echo cancellation (AEC). AEC is an algorithm which is able to detect when sounds or utterences reenter the audio input of the VTC codec, which came from the audio output of the same system, after some time delay. If unchecked, this can lead to several problems including 1) the remote party hearing their own voice coming back at them (usually significantly delayed) 2) strong reverberation, rendering the voice channel useless as it becomes hard to understand and 3) howling created by feedback. Echo cancellation is a processor-intensive task that usually works over a narrow range of sound delays. Multipoint videoconferencingSimultaneous videoconferencing among three or more remote points is possible by means of a Multipoint Control Unit (MCU). This is a bridge that interconnects calls from several sources (in a similar way to the audio conference call). All parties call the MCU unit, or the MCU unit can also call the parties which are going to participate, in sequence. There are MCU bridges for IP and ISDN-based videoconferencing. There are MCUs which are pure software, and others which are a combination of hardware and software. An MCU is characterised according to the number of simultaneous calls it can handle. MCUs can be stand-alone hardware devices, or they can be embedded into dedicated VTC units. StandardsThe International Telecommunications Union (ITU) (formerly: Consultative Committee on International Telegraphy and Telephony (CCITT)) has three umbrellas of standards for VTC.
In recent years, IP based videoconferencing has emerged as a common communications interface and standard provided by VTC manufacturers in their traditional ISDN-based systems. Business, government and military organizations still predominantly use H.320 and ISDN VTC. Though, due to the price point and proliferation of the Internet, and broadband in particular, there has been a strong spurt of growth and use of H.323, IP VTC. H.323 has the advantage that it is accessible to anyone with a high speed Internet connection, such as DSL. In addition, an attractive factor for IP VTC is that it is easier to set-up for use with a live VTC call along with data collaboration [web conferencing (ITU T.120 standard)]. These combined technologies enable users to have a much richer multimedia environment for live meetings, collaboration and presentations. Impact on the general publicHigh speed Internet connectivity has become more widely available at a reasonable cost and the cost of video capture and display technology has decreased. Consequently personal video teleconference systems based on a webcam, personal computer system, software compression and broadband Internet connectivity have become affordable for the general public. Also, the hardware used for this technology has continued to improve in quality, and prices have dropped dramatically. The availability of free software (often as part of chat programs) has made software based videoconferencing accessible to many. For many years, futurists have envisioned a future where telephone conversations will take place as actual face-to-face encounters with video as well as audio. Desktop PC videoconferencing can make this a reality. Impact on educationVideoconferencing provides students with the opportunity to learn by participating in a 2-way communication platform. Furthermore, teachers and lecturers from all over the world can be brought to classes in remote or otherwise isolated places. Students from diverse communities and backgrounds can come together to learn about one another. Students are able to explore, communicate, analyze and share information and ideas with one another. Through video conferencing students can visit another part of the world to speak with others, visit a zoo, a museum and so on, to learn. These "virtual field trips" can bring opportunities to children, especially those in geographically isolated or the economically disadvantaged. Small schools can use this technology to pool resources and teach courses (such as foreign languages) which otherwise couldn't be offered. Teachers can use this technology to acquire additional college credits for recertification without driving to classes. Impact on medicine and healthVideoconferencing is a very useful technology for telemedicine and telenursing applications, such as diagnosis, consulting, transmission of medical images, etc., in real time. Using VTC, patients may contact nurses and physicians in medical emergency or routine situations, physicians and other paramedical professionals can discuss cases across large distances. Rural areas can use this technology for diagnostic purposes, thus saving lives and making more efficient use of health care dollars. Special peripherals such as microscopes fitted with digital cameras, videoendoscopes, medical ultrasound imaging devices, otoscopes, etc., can be used in conjunction with VTC equipment to transmit data about a patient. Impact on businessVideoconferencing can enable individuals in faraway places to have meetings on short notice. Time and money that used to be spent in traveling can be used to have short meetings. Technology such as VOIP can be used in conjunction with desktop videoconferencing to enable face-to-face business meetings without leaving the desktop. Vendors and ProductsSome of the main manufacturers and solution providers are listed below. This is not an exhaustive list. Equipment manufacturers
Operating companies and Solution Providers
Software
External links
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