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Network Video Conferencing

A Network Conference, videoconference or videoteleconference is a set of interactive telecommunication technologies which allow two or more locations to interact simultaneously via two-way audio/video transmissions. Network Video Conferencing uses audio/video telecommunications to bring people in different locations together. This can be as simple as a conversation between two people in private offices (point-to-point) or involve several (multi-point) sites with more than one person in large rooms at different locations. Besides the audio/visual transmission of meeting activities, videoconferencing can be used to share documents and information.

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 specially equipped trucks became rather common.

Network Video Conferencing first was demonstrated in 1968. This technique was very expensive then 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. The greater 1 MHz bandwidth and 6 Mbit/s bit rate of Picturephone in the 1970s also did not cause the service to prosper.

It was only in the 1980s that digital telephony transmission networks became possible, such as ISDN, assuring a minimum bit rate (usually 128 kilobits/s) 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 1990s 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. In 1992 CU-SeeMe was developed at Cornell by Tim Dorcey et al., IVS was designed at INRIA, VTC arrived to the masses and free services, web plugins and software, such as NetMeeting, MSN Messenger, Yahoo Messenger, SightSpeed, Skype and others brought cheap, albeit low-quality, VTC.

Network Video Conferencing Technology:

Dual plasma display videoconferencing system. The screen on the left is primarily used to show people during the conference or the user interface when setting up the call. The one on the right shows data in this case but can display a 2nd 'far site' in a multipoint call.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 1s and 0s 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 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 VTC system include:

• Video input : video camera or webcam
• Video output: computer monitor , television or projector
• 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 (manufactured by companies such as Polycom, Sony, Tandberg, Radvision Ltd., and LifeSize) 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 meeting 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 PCs[1], 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. Videoconferences carried out via dispersed PCs are also known as e-meetings.

Network Video Conferencing 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 utterances 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 Network Video Conferencing:

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, its ability to conduct transposing of data rates and protocols, and features such as Continuous Presence, in which multiple parties can be seen onscreen at once.

MCUs can be stand-alone hardware devices, or they can be embedded into dedicated VTC units.

Some systems are capable of multipoint conferencing with no MCU, stand-alone, embedded or otherwise. These use a standards-based H.323 technique known as "decentralized multipoint", where each station in a multipoint call exchanges video and audio directly with the other stations with no central "manager" or other bottleneck. The advantages of this technique are that the video and audio will generally be of higher quality because they don't have to be relayed through a central point. Also, users can make ad-hoc multipoint calls without any concern for the availability or control of an MCU. This added convenience and quality comes at the expense of some increased network bandwidth, because every station must transmit to every other station directly.

Network Video Conferencing 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 videoconferencing 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" (see history of virtual learning environments) can bring opportunities to children, especially those in geographically isolated locations, or the economically disadvantaged. Small schools can use this technology to pool resources and teach courses (such as foreign languages) which could not otherwise be offered.

Here are a few examples of how videoconferencing can benefit people around campus:

• faculty member keeps in touch with class while away for a week at a conference
• guest lecturer brought into a class from another institution
• researcher collaborates with colleagues at other institutions on a regular basis without loss of time due to travel
• faculty member participates in a thesis defense at another institution
• administrators on tight schedules collaborate on a budget preparation from different parts of campus
• faculty committee auditions a scholarship candidate
• researcher answers questions about a grant proposal from an agency or review committee
• student interviews with an employer in another city
• Teleseminar

Source References and additional reading:

• Using "Skype" for Desktop Video Conferences 2008, Skype Video-Conference Guide
• Jim Van Meggelen 2005, The problem with video conferencing.
• Vertegaal, "Explaining Effects of Eye Gaze on Mediated Group Conversations: Amount or Synchronization?" ACM Conference on Computer Supported Cooperative Work, 2002.).
• Computer vision approaches to achieving eye contact appeared in the 1990s, such as Teleconferencing Eye Contact Using a Virtual Camera, ACM CHI 1993. More recently gaze correction systems using only a single camera have been shown, such as. Microsoft's GazeMaster system.
• Wolfe, Mark. “Broadband videoconferencing as knowledge management tool,” Journal of Knowledge Management 11, no. 2 (2007)
• Wikipedia.org, the free encyclopedia

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