There are basically two kinds
of VC systems:
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. Omni directional 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 VC devices:
- Large group VC are non-portable, large, more
expensive devices used for large rooms and
auditoriums.
- Small group VC are non-portable or portable,
smaller, less expensive devices used for small meeting
rooms.
- Individual VC 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 PC's, transforming them into VC
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. Video conferences
carried out via dispersed PCs are also known as
e-meetings.
Multipoint videoconferencing:
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.MCUs can be
stand-alone hardware devices, or they can be embedded into
dedicated VC units.
Standards:
The International Telecommunications Union (ITU)
(formerly: Consultative Committee on International
Telegraphy and Telephony (CCITT)) has three umbrellas of
standards for VC.
- ITU H.320 is known as the standard for public switched
telephone networks (PSTN) or VC over integrated services
digital networks (ISDN) basic rate interface (BRI) or
primary rate interface (PRI). H.320 is also used on
dedicated networks such as T1 and satellite-based
networks;
- ITU H.323 is known as the standard for video over
Internet Protocol (IP). This same standard also applies to
voice over IP VoIP);
- ITU H.324 is the standard for transmission over POTS,
or audio telephony networks.
In recent years, IP based videoconferencing has emerged
as a common communications interface and standard provided
by VC manufacturers in their traditional ISDN-based systems.
Business, government and military organizations still
predominantly use H.320 and ISDN VTC. Though, due to the
price point and proliferation of the Internet, and broadband
in particular, there has been a strong spurt of growth and
use of H.323, IP VC. H.323 has the advantage that it is
accessible to anyone with a high speed Internet connection,
such as DSL.
In addition, an attractive factor for IP VC is that it
is easier to set-up for use with a live VC call along with
data collaboration [web conferencing (ITU T.120
standard)]. These combined technologies enable users to have
a much richer
multimedia environment for live meetings, collaboration
and presentations.
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