video conference

from Wikipedia, the free encyclopedia
A French soldier during a video conference (2006)
Video conference between the ISS space station and the White House (2011)

The video conference is the synchronous exchange of information for image and sound transmission. At least one camera and microphone as input devices as well as a screen and a loudspeaker or headphones as output devices must be available. If there are only two participants, the term video telephony is more appropriate. If, on the other hand, the data is transmitted over the Internet, the term web conference is also common.

In the case of high-quality transmission with the creation of the illusion of sitting in the same room with the interlocutors connected via video, one speaks of telepresence .

history

The first developments in video conferencing technologies began as early as the 1930s, parallel to the development of television . Despite new technologies in the 1970s and the resulting resumption of development, video conferencing was not very widespread until the beginning of the third millennium. A breakthrough was achieved by improved compression methods for the now completely digitized voice and video data, the standardization of the previously proprietary methods and the general availability of PCs and digitized connection lines to initial successes.

At CeBit 1993, the Aachen-based company Datus presented the first video conference system in which the speech was compressed by a factor of 10.

With the increasing switch to IP-based switching technology, video conferencing is benefiting more and more from the availability of broadband connections. Experts therefore predict that this communication technology will become more widespread. A big advantage of video conferencing is that it saves time and resource consuming travel. ( See also: Green IT )

Web conference as the most uncomplicated form of video conference

Main article: Web conference

Due to today's general availability of computers with webcams or smartphones and a well-developed Internet , a video conference can now be held very easily using appropriate services. Some of these services and the corresponding client software are available free of charge for private use. In addition to the transmission of webcam videos recorded on the computer and spoken language ( VoIP ), it is also possible to add a telephone conference or a mixture of telephone conference and computer audio.

To set up a conference, the desired participants are invited by a host, for example by e-mail, and receive an ID or an Internet link to join the conference. Participants can be muted during the conference. This is particularly common at large conferences. However, it is also possible to give the floor to individual participants. The web conference enables screen contents (such as documents) of a participant to be displayed on all participant screens ( screen sharing ). There are chats and areas for questions and answers. The messages can be sent confidentially to certain participants or publicly to all participants, depending on the settings.

The number of participants can go into the thousands, but then usually only certain participants send multimedia data. Such a special form of video conference is also known as a webcast or webinar .

Technical aspects

The technical basis of the transmission

The standardization authority ITU-T defines four major groups of devices:

Video conference terminals

The video conferencing market offers a number of system and implementation variants, the equipment of which essentially depends on the intended use.

Desktop systems With desktop systems , the necessary components are built into a PC . It is this addition of an external camera (now mostly USB - Webcam ) and a microphone or headset required. A distinction is made between hardware-based ( coding and decoding on a plug-in card ) and purely software-based desktop systems. In addition to the relatively low costs, desktop systems have the advantage that the user has full access to his data and the programs installed on the PC during the video conference . Desktop systems are therefore particularly suitable where joint data processing is to take place in the context of conferences.

Set-top boxes / rollabouts These compact systems are special devices that usually only require a monitor and the corresponding network connections ( ISDN and / or LAN )to operate. Due to their low weight and easy installation , these devices are also suitable for mobile use.

Room systems Room systems are modular , high-performance systems. System configurations for almost any application are possible thanks to variable equipment features . Powerful cameras, room microphones and large monitors allow these systems to be installed even in large conference rooms, which also enable the integration of other peripheral devices such as document cameras .

Other devices These include the mobile radio video conference via UMTS or video telephony, which is currently under development .

Multipoint Control Unit (MCU)

MCUs are star distributors - also known as reflectors - for group conferences. They are always necessary if more than two participants want to take part in a conference. These are hardware and / or software solutions that manage and control one or more multipoint conferences. The MCU is connected to all participants. It manages and regulates the incoming and outgoing video and audio data streams . In Germany , for example, MCUs are used within the DFN association to operate its VideoConference service. But also companies and large state administrations such as B. in NRW or Bavaria use MCUs for video communication. MCUs may support a. the H.323 and SIP protocols .

Gatekeeper

The gatekeeper is a central logical component of the video conference, which, among other things , can organize the establishment of a connection between the end devices and the MCU. It can also forward the data streams as a proxy . All devices that are assigned to a gatekeeper are in the same zone (similar to the area code on the telephone). Address translations are carried out with a gatekeeper.

Gateway

A gateway connects different networks with one another and is implemented via OSI layers 4 to 7. Gateways convert protocols into one another, but can also take over the coupling of two networks. When using ISDN and IP terminal devices together, the use of a gateway is essential.

Protocols as the basis of transmission

The H.320, H.323 and T.120 protocols form an important part of the technical basis. These protocols are so-called umbrella standards , which also contain other protocols on individual aspects.

The H.323 protocol

The most important protocol for operation on the Internet is the H.323 protocol . The standard regulates the collaboration for video telephony devices that are connected via a LAN / WAN . Within the framework of H.323, the H.225 protocol regulates the control of the connection and the implementation of IP addresses; the devices use H.245 to agree which services they support. This mainly applies to video compression according to H.261 , H.263 or H.264 and audio coding from G.711 to G.729.

The H.320 protocol

The H.320 protocol regulates the operation of narrow-band video telephony terminals (e.g. ISDN, satellite, radio relay) and, like H.323, contains further framework specifications.

The protocol T.120

With the help of the T.120 protocol , data applications are implemented within a video conference. It comprises nine guidelines that define in detail connection establishment and disconnection, flow control , cooperation with MCUs, the use of interactive whiteboards , file transfer and application sharing .

The standard H.239

A classic video conference has an audio, a video and optionally a data channel. H.239 defines the method of using a second video channel when using the H.320 and H.323 protocols to e.g. B. to show a presentation as a video or the image of a second camera. H.239 thus replaces proprietary processes (e.g. People + Content, DuoVideo). However, none of these methods allow application sharing, since mutual access to the data is not possible.

The SIP protocol

The Session Initiation Protocol (SIP) was developed for the transmission of multimedia applications. SIP is distantly similar to HTTP and is not compatible with H.323 or H.320. It is used to negotiate the communication modalities, the communication is agreed within the SIP packets via the Session Description Protocol (SDP). The data transfer itself then usually takes place directly between the endpoints using other Internet protocols such as the Real Time Transport Protocol .

Proprietary peer-to-peer systems

Peer-to-Peer (P2P) video conference systems do without central group and communication servers, as is the case with H.323 systems through gatekeepers and MCUs. Instead, group and quality of service management is shifted to the end devices. P2P video conference systems are mostly desktop systems. They are proprietary systems and are not subject to any standardization. Examples of P2P video conference systems are the Bravis system of the BTU Cottbus , the daViKo system (developed at the FHTW Berlin ) and Skype .

Application software

Common computer programs for video conferencing are Skype , Google Hangouts , FaceTime , Jitsi , WebEx , TeamViewer and WebRTC -based programs.

Social dynamism

Video conferences represent an independent communication situation that is not just in the middle between traditional telephone and face-to-face communication. The most important problem here is that the spatially separated locations of the participants result in different perceptual conditions.

The answer to the question of whether the participants in a video conference make more use of the video or audio stream depends on the topic of the conversation. If non-verbal or deictic aspects play a major role, the video comes to the fore, whereas for all other topics, the participants mostly concentrate on the audio stream.

A common communication problem in video conferences is the time lag of up to one second between recording and broadcasting. This lag often has the consequence that the other interlocutor is perceived as "slow" or a pause in transmission is misinterpreted to mean that the expected, but supposedly missing answer is interrupted. Further problems are the difficulty in making eye contact, especially because the self-image is often preferred and technical problems such as picture or sound loss or coarse pixelation.

Web links

Commons : Videoconferencing  - collection of pictures, videos and audio files
Wiktionary: Videoconferencing  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Olaf A. Schulte, Martin Friebel, Christian Klotzek: Recording of Technically Mediated Communication - The Example of Video Conference. In: Conversation Research. 2, 2001, p. 226. (PDF)
  2. ↑ CeBit 1993
  3. ↑ IT-DLZ Bayern: product sheet video conference switching system
  4. ↑ H.239 standard H.239 standard at ITU-T (English)
  5. ^ Art Blokland, Anne H. Anderson: Effect of low frame-rate video on intelligibility of speech. In: Speech Communication. 26 (1-2), 1998, p. 97.
  6. ^ Olaf A. Schulte, Martin Friebel, Christian Klotzek: Recording of Technically Mediated Communication - The Example of Video Conference. In: Conversation Research. 2, 2001, p. 227. (PDF)
  7. ↑ Martin Friebel, Jens Loenhoff, H. Walter Schmitz, Olaf A. Schulte: "Do you see me?" - "Do you hear me?" - Video conferences as a subject of research in communication studies. In: communication @ society. 4, 2003, p. 16f. (PDF) ( Memento from July 4, 2009 in the Internet Archive )
  8. ↑ Marc Körschen, Jessica Pohl, H. Walter Schmitz, Olaf A. Schulte: New techniques of qualitative research interview: Computer-aided transcription of video conferencing. In: Forum Qualitative Social Research - FQS. 3 (2), 2002, p. 19, paras. 5-13. qualitative-research.net
  9. ↑ Joel S. Angiolillo, Harry E. Blanchard, Edmond W. Israelski: Video Telephony and Teleconferencing. In: AT&T Technical Journal. 72 (3), 1991, p. 18.
  10. ↑ Martin Friebel, Jens Loenhoff, H. Walter Schmitz, Olaf A. Schulte: "Do you see me?" - "Do you hear me?" - Video conferences as a subject of research in communication studies. In: communication @ society. 4, 2003, p. 10f. (PDF) ( Memento from July 4, 2009 in the Internet Archive )
  11. ↑ Marc Körschen, Jessica Pohl, H. Walter Schmitz, Olaf A. Schulte: New techniques of qualitative research interview: Computer-aided transcription of video conferencing. In: Forum Qualitative Social Research - FQS. 3 (2), 2002, p. 19, para. 28ff. qualitative-research.net
  12. ↑ Marc Körschen, Jessica Pohl, H. Walter Schmitz, Olaf A. Schulte: New techniques of qualitative research interview: Computer-aided transcription of video conferencing. In: Forum Qualitative Social Research - FQS. 3 (2), 2002, p. 19, para. 37ff. qualitative-research.net