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.
History
Simple 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.
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 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.
Technology
The 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:
- 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 piece of equipment, usually a console with a high quality remote controlled video camera. These cameras can be controlled at a distance to pan left and right, tilt up and down, and zoom. They became known as PTZ cameras. The console contains all electrical interfaces, the control computer, and the software or hardware-based codec. Omnidirectional microphones are connected to the console, as well as a TV monitor 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.
- Small group VTC are non-portable or portable, smaller, less expensive devices used for small meeeting rooms.
- 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 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). 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 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 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.
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 is 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 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 public
High 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 set-up, software compression and broadband Internet connectivity have become affordable for the general public. Furthermore, the availability of free software (often as part of chat programs) has made software based videoconferencing 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 on, 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
Some of the main manufacturers and solution providers are listed below. This is not an exhaustive list.
Equipment manufacturers
- Aethra S.p.A
- Codian
- Lifesize Communications
- Phoenix Audio Technologies
- Polycom
- Radvision
- Sony
- Tandberg
- iSight (Apple)
Operating companies and Solution Providers
- Access Grid
- Australian Videophone Network
- Camfrog
- DyLogic
- GlowPoint
- inSORS
- Marratech
- MegaMeeting
- NIAD
- InstantPresenter
- iVisit
- Videocall
Software
- AOL Instant Messenger
- Camfrog
- Ekiga
- iChat AV
- ICUII
- inSORS
- Interactive Networks Inc.
- Marratech
- Mirial
- Microsoft NetMeeting
- MSN Messenger
- SeeNx
- Session
- SightSpeed
- Skype
- Tlen
- Virtual Room Videoconferencing System (VRVS)
- Yahoo Messenger
External links
- ViDe Videoconferencing Cookbook
- http://www.cybartv.org research & developments videoconferencing applications webTV & interactives TV