Technology the core technology used in a

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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 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 video telephony, because they convert the digital pulses to/from analog waves in the audio spectrum range. Common components in a standard VTC network are Call Server , Video Endpoint , Multipoint Conference Unit (MCU) , Gateways, and an Ethernet switch. A Call Server performs the registration and call control processing functions. Video
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245 Endpoints are devices from which users make and receive video calls. The endpoint processes the bi-directional audio, video, and data streams and interfaces to the users. 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. 20.3.6. TYPE OF VTC SYSTEMS The two basic types of VTC systems are the dedicated systems and the desktop systems. 1) Dedicated systems have all required components packaged into a single piece of equipment, usually a console with a high quality 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. Thus, dedicated systems have all the necessary components to process the VTC sessions within a single console. The categories of dedicated VTC systems cover different operational environments. The several types of dedicated videoconferencing devices are: i) The first category is large group VTC system. Large group videoconferencing is a non-portable, large, more expensive device that is fixed to the room. It supports large meeting rooms or auditoriums.
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