Videoconferencing
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Wikipedia-Article "Videoconferencing"
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.
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History
Simple analog videoconferencing systems could be established as early as the invention of television proper. It was usually accomplished by setting up two closed circuit television systems using cable. Eventually, NASA did the first manned space flights, using two radiofrequency (UHF of 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.
This 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 bad 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 then 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 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 also 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.
Technology
The core technology using in a videoteleconference (VTC) system is in digital compression of audio and video streams in real time. The hardware or software that does that 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 into/from analog waves in the audio spectrum range.
The other components required for a VTC system include:
- video input: video camera or webcam
- video output: computer monitor or television
- audio input: microphones
- audio output: usually loudspeakers associated with the display device or telephone
- data transfer: analog or digital telephone network, LAN or Internet
There are basically two kinds of VTC systems:
- Dedicated systems have all required components packaged into a single equipment, usually a console with a high quality remote controlled video camera on its top. These cameras can be controlled at a distance to move in the horizontal and vertical directions (pan and tilt, respectively) as well as to perform image zooming, so they are called PTZ cameras. The console contains all electrical interfaces, the control computer, modem, and the software- or hardware-based codec. Omnidirectional microphones are connected to the console, as well as a monitor TV with loudspeakers and/or a video projector. There are several types of dedicated VTC devices:
- Large group VTC are non-portable, large, more expensive devices used for large rooms and auditoriums. Use of PTZ cameras is practically mandatory.
- Small group VTC are non-portable or portable, smaller, less expensive devices used for small meeeting rooms (e.g., up to 10 people) and PTZ cameras are usual
- Individual VTC are usually portable devices, meant for single users, have fixed cameras, microphones and loudspeakers integrated into the console.
- Desktop systems are add-ons (hardware boards, usually) to normal PC's, transforming them into VTC devices. A range of different cameras and microphones can be used with the board, which contains the necessary codec and transmission interfaces. Most of the desktops systems work only with the H.323 standard. Video conferences carried out via dispersed PCs are also known as e-meetings.
Echo cancellation
A fundamental feature of professional VTC systems is acoustic echo cancellation (AEC). It is an algorithm which is able to detect when sounds or voice reenters the audio input of the VTC codec, coming from the audio output of the same system, after some time delay, which is introduced by the travel time of digital voice over the network connecting the two VTC devices. If uncchecked, this can lead 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 voice and 3) howling created by feedback. Echo cancellation is a processing-intensive task that usually works over a narrow range of sound delays.
Multipoint videoconferencing
Simultaneous 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 well-known audio conference call). All parties call the network ID number of 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 MCU which are pure software, and others which are a combination of hardware and software. A 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 TVC units.
Standards
The International Telecommunications Union (ITU) (formerly: Consultative Committee on International Telegraphy and Telephony (CCITT)) has three umbrellas of standards for VTC.
- ITU H.320 is known as the standard for public switched telephone networks (PSTN) or VTC over integrated services digital networks (ISDN) basic rate interface (BRI) or primary rate interface (PRI). H.320 also used on dedicated networks such as T1 and satellite-based networks;
- ITU H.323 is known as the standard for video over Internet Protocol (IP). This same standard also applies to voice over IP VoIP);
- ITU H.324 is the standard for transmission over POTS, or audio telephony networks.
In recent years, IP based videoteleconferencing 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 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 ADSL, computer, webcam, microphone and speaker or headset.
In addition, an attraction factor for IP VTC is that it 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 efforts and presentations.
Impact on the general public
As high speed Internet connectivity has become more widely available at a reasonable cost and the cost of video capture and display technology has decreased, personal video teleconference systems based on a webcam, personal computer system set-up, software compression and broadband Internet connection have become affordable for the general public. Furthermore, the availability of free software (often as part of chat programs) has made the software accessible to many.
Impact on education
Videoconferencing 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 much to learn.
Impact on medicine and health
Videoconferencing 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, etc.
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.
Vendors and Products
Equipment manufacturers
Operating companies and Solution Providers
- 2Much Internet Services
- Access Grid
- Australian Videophone Network (www.avn.net.au)
- Camfrog Webcam Chat
- GlowPoint
- Marratech (official site)
- MegaMeeting.com
- InstantPresenter Web Conferencing (official site)
- iVisit
Software
- Sony IVE (official site)
- AOL Instant Messenger (official site)
- GnomeMeeting (official site)
- HomeMeeting JoinNet (official site)
- iChat AV (official site)
- InstantPresenter Web Conferencing (official site)
- Isabel Application Multipoint without MCU (official site) (more)
- Interactive Networks Inc. (official site)
- iVisit (official site)
- Marratech (official site)
- MegaMeeting (official site)
- Microsoft NetMeeting (official site)
- MSN Messenger (official site)
- SeeNx (official site)
- Session (official site)
- SightSpeed
- Skype (official site)
- Tlen
- Virtual Room Videoconferencing System (VRVS) (official site)
- WobCast (official site)
- Yahoo Messenger (official site)
External links
- http://www.conferencing-guide.com/video-conferencing.php - online resource for learning about video conferencing
- LIVE! Videoconferencing - Multi-speaker videoconferencing with up to 150 persons at once
- Meeting On Now - Video and audio conferencing using P2P technology
- http://www.microsoft.com/windows/netmeeting/ - Microsoft Netmeeting website
- http://thinkofit.com/webconf/video.htm - Comprehensive resource list of video conferencing vendors, products, and services
- http://www.videnet.gatech.edu/cookbook.en/ - ViDe Videoconferencing Cookbook
- WigiWigi - Real-time multi IM Video Conferencing