2016/4/23 VideoconferencingWikipedia,thefreeencyclopedia
https://en.wikipedia.org/wiki/Videoconferencing 1/20
A Tandberg T3 high resolution
telepresence room in use
(2008).
Indonesian and U.S. students
participating in an
educational videoconference
(2010).
Videoconferencing
From Wikipedia, the free encyclopedia
Videoconferencing (VC) is the conduct of a
videoconference (also known as a video conference
or videoteleconference) by a set of
telecommunication technologies which allow two or
more locations to communicate by simultaneous two-
way video and audio transmissions. It has also been
called 'visual collaboration' and is a type of
groupware.
Videoconferencing differs from videophone calls in
that it's designed to serve a conference or multiple
locations rather than individuals.
[1]
It is an
intermediate form of videotelephony, first used
commercially in Germany during the late-1930s and
later in the United States during the early 1970s as
part of AT&T's development of Picturephone
technology.
With the introduction of relatively low cost, high
capacity broadband telecommunication services in the
late 1990s, coupled with powerful computing
processors and video compression techniques,
videoconferencing has made significant inroads in
business, education, medicine and media.
Contents
1 History
2 Technology
2.1 Conferencing layers
2.2 Multipoint videoconferencing
2.3 Videoconferencing modes
2.4 Echo cancellation
2.5 Cloud-based video conferencing
3 Technical and other issues
4 Standards
5 Social and institutional impact
5.1 Impact on the general public
5.2 Impact on government and law
5.3 Impact on education
5.4 Impact on medicine and health
5.5 Impact on sign language
communications
5.6 Impact on business
5.7 Impact on media relations
6 Descriptive names and terminology
7 See also
2016/4/23 VideoconferencingWikipedia,thefreeencyclopedia
https://en.wikipedia.org/wiki/Videoconferencing 2/20
Multiple user
videoconferencing first being
demonstrated with Stanford
Research Institute's NLS
computer technology (1968).
7 See also
8 References
9 Further reading
History
Videoconferencing uses audio and video
telecommunications to bring people at different
sites together. This can be as simple as a
conversation between people in private offices
(point-to-point) or involve several (multipoint)
sites in large rooms at multiple locations. Besides
the audio and visual transmission of meeting
activities, allied videoconferencing technologies
can be used to share documents and display
information on whiteboards.
Simple analog videophone communication could be
established as early as the invention of the
television. Such an antecedent usually consisted of
two closed-circuit television systems connected via
coax cable or radio. An example of that was the German Reich Postzentralamt (post
office) video telephone network serving Berlin and several German cities via coaxial
cables between 1936 and 1940.
[2][3]
During the first manned space flights, NASA used two radio-frequency (UHF or VHF)
video links, one in each direction. TV channels routinely use this type of
videotelephony when reporting from distant locations. The news media were to become
regular users of mobile links to satellites using specially equipped trucks, and
much later via special satellite videophones in a briefcase.
This technique was very expensive, though, and could not be used for applications
such as telemedicine, distance education, and business meetings. Attempts at using
normal telephony networks to transmit slow-scan video, such as the first systems
developed by AT&T Corporation, first researched in the 1950s, failed mostly due to
the poor picture quality and the lack of efficient video compression techniques. The
greater 1MHz bandwidth and 6 Mbit/s bit rate of the Picturephone in the 1970s also
did not achieve commercial success, mostly due to its high cost, but also due to a
lack of network effect —with only a few hundred Picturephones in the world, users
had extremely few contacts they could actually call to, and interoperability with
other videophone systems would not exist for decades.
It was only in the 1980s that digital telephony transmission networks became
possible, such as with ISDN networks, assuring a minimum bit rate (usually 128
kilobits/s) for compressed video and audio transmission. During this time, there was
also research into other forms of digital video and audio communication. Many of
these technologies, such as the Media space, are not as widely used today as
videoconferencing but were still an important area of research.
[4][5]
The first
dedicated systems started to appear in the market as ISDN networks were expanding
2016/4/23 VideoconferencingWikipedia,thefreeencyclopedia
https://en.wikipedia.org/wiki/Videoconferencing 3/20
Global Schoolhouse students
communicating via CU-SeeMe,
with a video framerate between
3-9 frames per second (1993).
throughout the world. One of the first commercial videoconferencing systems sold to
companies came from PictureTel Corp., which had an Initial Public Offering in
November, 1984.
In 1984 Concept Communication in the United States replaced the then-100 pound,
US$100,000 computers necessary for teleconferencing, with a $12,000 circuit board
that doubled the video frame rate from 15 up to 30 frames per second, and which
reduced the equipment to the size of a circuit board fitting into standard personal
computers.
[6]
The company also secured a patent for a codec for full-motion
videoconferencing, first demonstrated at AT&T Bell Labs in 1986.
[6][7]
Videoconferencing systems throughout the 1990s
rapidly evolved from very expensive proprietary
equipment, software and network requirements to a
standards-based technology readily available to the
general public at a reasonable cost.
Finally, in the 1990s, Internet Protocol-based
videoconferencing became possible, and more
efficient video compression technologies were
developed, permitting desktop, or personal computer
(PC)-based videoconferencing. In 1992 CU-SeeMe was
developed at Cornell by Tim Dorcey et al. In 1995
the first public videoconference between North
America and Africa took place, linking a technofair in San Francisco with a techno-
rave and cyberdeli in Cape Town. At the Winter Olympics opening ceremony in Nagano,
Japan, Seiji Ozawa conducted the Ode to Joy from Beethoven's Ninth Symphony
simultaneously across five continents in near-real time.
While videoconferencing technology was initially used primarily within internal
corporate communication networks, one of the first community service usages of the
technology started in 1992 through a unique partnership with PictureTel and IBM
Corporations which at the time were promoting a jointly developed desktop based
videoconferencing product known as the PCS/1. Over the next 15 years, Project DIANE
(Diversified Information and Assistance Network) grew to utilize a variety of
videoconferencing platforms to create a multi-state cooperative public service and
distance education network consisting of several hundred schools, neighborhood
centers, libraries, science museums, zoos and parks, public assistance centers, and
other community oriented organizations.
In the 2000s, videotelephony was popularized via free Internet services such as
Skype and iChat, web plugins and on-line telecommunication programs that promoted
low cost, albeit lower-quality, videoconferencing to virtually every location with
an Internet connection.
In May 2005, the first high definition video conferencing systems, produced by
LifeSize Communications, were displayed at the Interop trade show in Las Vegas,
Nevada, able to provide video at 30 frames per second with a 1280 by 720 display
resolution.
[8][9]
Polycom introduced its first high definition video conferencing
2016/4/23 VideoconferencingWikipedia,thefreeencyclopedia
https://en.wikipedia.org/wiki/Videoconferencing 4/20
Russian President Dmitry
Medvedev attending the
Singapore APEC summit, holding
a videoconference with Rashid
Nurgaliyev via a Tactical MXP,
after an arms depot explosion
in Russia (2009).
Dual display: An older Polycom
VSX 7000 system and camera
used for videoconferencing,
with two displays for
simultaneous broadcast from
separate locations (2008).
system to the market in 2006. As of the 2010s, high
definition resolution for videoconferencing became a
popular feature, with most major suppliers in the
videoconferencing market offering it.
Technological developments by videoconferencing
developers in the 2010s have extended the
capabilities of video conferencing systems beyond
the boardroom for use with hand-held mobile devices
that combine the use of video, audio and on-screen
drawing capabilities broadcasting in real-time over
secure networks, independent of location. Mobile
collaboration systems now allow multiple people in
previously unreachable locations, such as workers on
an off-shore oil rig, the ability to view and
discuss issues with colleagues thousands of miles
away. Traditional videoconferencing system
manufacturers have begun providing mobile applications as well, such as those that
allow for live and still image streaming.
[10]
Technology
The core technology used in a videoconferencing
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 1s
and 0s is subdivided into labeled 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 Old Telephone System, 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
videoconferencing system include:
Video input: video camera or webcam
Video output: computer monitor, television or projector
Audio input: microphones, CD/DVD player, cassette player, or any other source
of PreAmp audio outlet.
Audio output: usually loudspeakers associated with the display device or
telephone
Data transfer: analog or digital telephone network, LAN or Internet
Computer: a data processing unit that ties together the other components, does
the compressing and decompressing, and initiates and maintains the data linkage
via the network.
2016/4/23 VideoconferencingWikipedia,thefreeencyclopedia
https://en.wikipedia.org/wiki/Videoconferencing 5/20
Various components and the
camera of a LifeSize
Communications Room 220 high
definition multipoint system
(2010).
A video conference meeting
facilitated by Google
Hangouts.
There are basically two kinds of videoconferencing
systems:
1. 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
videoconferencing devices:
1. Large group videoconferencing are non-
portable, large, more expensive devices
used for large rooms and auditoriums.
2. Small group videoconferencing are non-
portable or portable, smaller, less
expensive devices used for small meeting
rooms.
3. Individual videoconferencing are usually
portable devices, meant for single users,
have fixed cameras, microphones and
loudspeakers integrated into the console.
2. Desktop systems are add-ons (hardware boards or
software codec) to normal PCs and laptops,
transforming them into videoconferencing devices. A range of different cameras
and microphones can be used with the codec, which contains the necessary codec
and transmission interfaces. Most of the desktops systems work with the H.323
standard. Videoconferences carried out via dispersed PCs are also known as e-
meetings. These can also be nonstandard, Microsoft Lync, Skype for Business,
Google Hangouts, or Yahoo Messenger or standards based, Cisco Jabber.
3. WebRTC Platforms are video conferencing solutions that are not resident by
using a software application but is available through the standard web browser.
Solutions such as Adobe Connect and Cisco WebEX can be accessed by going to a
URL sent by the meeting organizer and various degrees of security can be
attached to the virtual "room". Often the user will be required to download a
piece of software, called an "Add In" to enable the browser to access the local
camera, microphone and establish a connection to the meeting.
Conferencing layers
The components within a Conferencing System can be divided up into several different
layers: User Interface, Conference Control, Control or Signal Plane, and Media
Plane.
Videoconferencing User Interfaces (VUI) can be either graphical or voice responsive.
Many in the industry have encountered both types of interfaces, and normally
graphical interfaces are encountered on a computer. User interfaces for conferencing
- 1
- 2
前往页