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Videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio and video signals by people in different locations for real time communication. A videophone is a telephone with a video camera and video display, capable of simultaneous video and audio communication. Videoconferencing implies the use of this technology for a group or organizational meeting rather than for individuals, in a videoconference. Telepresence may refer either to a high-quality videotelephony system (where the goal is to create the illusion that remote participants are in the same room) or to meetup technology, which can go beyond video into robotics (such as moving around the room or physically manipulating objects). Videoconferencing has also been called "visual collaboration" and is a type of groupware.
While development of video - conferring started in the late 19th century, the technology only became available to the public starting in the 1930s. These early demonstrations were installed at "booths" in post offices and shown at various world expositions. It took until 1970 for AT&T to launch the first true video-conferring system, where anyone could subscribe to the service and have the technology in their home or office. Video telephony also included "image phones" which would exchange still images between units every few seconds over conventional plain old telephone service (POTS) lines, essentially the same as slow-scan TV. The development of advanced video codecs, more powerful CPUs, and high-bandwidth Internet service in the late 1990s allowed videophones to provide high-quality low-cost color service between users almost any place in the world where the Internet is available.
Although not as widely used in everyday communications as audio-only and text communication, useful applications include sign language transmission for deaf and speech-impaired people, distance education, telemedicine, and overcoming mobility issues. It is also used in commercial and corporate settings to facilitate meetings and conferences, typically between parties that already have established relationships. News media organizations have begun to use desktop technologies like Skype to provide higher-quality audio than the cellular phone network, and video links at much lower cost than sending professional equipment or using a professional studio. Videoconferencing saw its earliest use with AT&T's Picturephone service in the early 1970s. Transmissions were analog over short distances, but converted to digital forms for longer calls, again using telephone transmission technology. Popular corporate video-conferencing systems in the present day have migrated almost exclusively to digital ISDN and IP transmission modes due to the need to convey the very large amounts of data generated by their cameras and microphones. These systems are often intended for use in conference mode, that is by many people in several different locations, all of whom can be viewed by every participant at each location. Videoconferencing systems—midrange cost, usually using multipoint control units or other bridging services to allow multiple parties on videoconference calls. Quality of service can vary from moderate to high. Computer security experts have shown that poorly configured or inadequately supervised videoconferencing systems can permit an easy "virtual" entry by computer hackers and criminals into company premises and corporate boardrooms. Videoconferencing systems use two methods to determine which video feed or feeds to display. Continuous Presence simply displays all participants at the same time, usually with the exception that the viewer either does not see their own feed, or sees their own feed in miniature. Voice-Activated Switch selectively chooses a feed to display at each endpoint, with the goal of showing the person who is currently speaking. This is done by choosing the feed (other than the viewer) which has the loudest audio input (perhaps with some filtering to avoid switching for very short-lived volume spikes). Often if no remote parties are currently speaking, the feed with the last speaker remains on the screen. The components within a videoconferencing system can be divided up into several different layers: User Interface, Conference Control, Control or Signaling Plane, and Media Plane.
Videoconferencing User Interfaces (VUI) can be either graphical or voice-responsive. Many in the industry have encountered both types of interface, and normally a graphical interface is encountered on a computer. User interfaces for conferencing have a number of different uses; they can be used for scheduling, setup, and making a videocall. Through the user interface the administrator is able to control the other three layers of the system.
Conference Control performs resource allocation, management, and routing. This layer along with the User Interface creates meetings (scheduled or unscheduled) or adds and removes participants from a conference.
Control (Signaling) Plane contains the stacks that signal different endpoints to create a call and/or a conference. Signals can be, but aren't limited to, H.323 and Session Initiation Protocol (SIP) Protocols. These signals control incoming and outgoing connections as well as session parameters.
The Media Plane controls the audio and video mixing and streaming. This layer manages Real-Time Transport Protocols, User Datagram Packets (UDP) and Real-Time Transport Control Protocol (RTCP). The RTP and UDP normally carry information such the payload type which is the type of codec, frame rate, video size, and many others. RTCP on the other hand acts as a quality control Protocol for detecting errors during streaming.
Distance education
Videoconferencing provides students with the chance to learn by participating in two-way communication forums. Because it is live, videotelephony allows teachers to access remote or otherwise isolated learners. Students from diverse communities and backgrounds can come together to learn about one another through practices known as telecollaboration^[58][59](in foreign language education) and virtual exchange, although language barriers will continue to be present. Such students are able to explore, communicate, analyze, and share information and ideas with one another.
Through videoconferencing, students can visit other parts of the world, including museums and other cultural and educational sites. Such virtual field trips can provide enriched learning opportunities to students, especially those who are geographically isolated or economically disadvantaged. Small schools can use these technologies to pool resources and provide courses, such as in foreign languages, which could not otherwise be offered.
Some benefits that videoconferencing can provide to education include:

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  faculty members keeping in touch with classes while attending conferences;
  
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  faculty members attending conferences 'virtually'^[60][61]
  
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  guest lecturers brought in classes from other institutions;^[62]
  
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  researchers collaborating with colleagues at other institutions on a regular basis without loss of time due to travel;
  
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  schools with multiple campuses collaborating and sharing professors;^[63]
  
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  schools from two separate nations engaging in cross-cultural exchanges;^[64]
  
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  faculty members participating in thesis defenses at other institutions;
  
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  administrators on tight schedules collaborating on budget preparation from different parts of campus;
  
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  faculty committee auditioning scholarship candidates;
  
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  researchers answering questions about grant proposals from agencies or review committees;
  
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  alternative enrollment structures to purely in-person attendance;
  
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  student interviews with employers in other cities, and
  
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  teleseminars.