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Transmission of a television signal in its original analog form (as it would
come from a TV camera), requires terrestrial television channels or a
satellite transponder. Terrestrial television channels are not readily
available for occasional corporate use; satellite transponders are available.
Most systems therefore, incorporate digital compression techniques to reduce
the bandwidth required for motion videoconferences. Example: An image in
motion is refreshed on a television screen 30 times per second. This means
that the bandwidth necessary to transmit the image is very high, usually 1.5
megabits per second (Mbps).
This bandwidth is beyond the capacity of the standard telephone cable. A
device called a "codec" digitizes the analog television signal and compresses
it by eliminating redundant information. Currently, codecs can reduce the
bandwidth to 56 kilobits per second (Kbps) and it is hoped that this bandwidth
can be compressed even further.
The resulting signal can be transmitted over less than full bandwidth
channels. The picture is of somewhat less quality than the original analog
image, but more than sufficient for most meetings.
FREEZE-FRAME Videoconferencing
------------------------------
Freeze-frame videoconferencing is like a slide show. It captures still images
either in color or black-and-white. Freeze-frame "stills" of people seem
unnatural and can be distracting. Yet, freeze-frame video is best for still
images of three-dimensional objects such as a product or a part, and for
charts, drawings, graphics, and specially prepared presentation material.
Freeze-Frame Transmission On Narrow Band Channels
-------------------------------------------------
A freeze-frame system captures an image by stopping, or freezing any motion
that might be present. The image can be transmitted via analog or digital
signals over narrow channels. These channels are considerably narrower than
those used for full-motion video conferencing. In its simplest form,
freeze-frame video can utilize ordinary telephone line transmission. A single
freeze-frame image will require at least 30 seconds to a minute or more for
transmission.
In some systems, the freeze-frame image is displayed line by line as it is
received. This creates a vertical "waterfall" effect or a horizontal scanning
effect. In other systems, the incoming lines of picture information are
stored in a buffer until the completed picture can be displayed as a whole.
In still other systems, an image emerges in successively better resolution as
additional picture information is received.
Enhancements To Freeze-Frame Video Systems
------------------------------------------
There are a number of ways to expand a freeze-frame video system's
capabilities. One enhancement is telewriting. With a "pen" connected to a
telewriting device, users can point out a portion of a freeze-frame video
image, overlaying lines and markings in various colors that are displayed at
all locations as they are drawn. Some telewriting devices include stored
geometric shapes, logos, and symbols that can be transmitted as overlays to a
freeze-frame image. Zoom capability enables close-up analysis of portions of
a display.
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Personal Computers and Desktop Videoconferencing
------------------------------------------------
Personal computers are beginning to be increasingly used with freeze-frame
videoconferencing. PCs are used for control, for the creation of graphics,
and for storage and retrieval of graphics material. There are signs that this
evolution towards desktop videoconferencing has already begun.
The MINX (Multimedia Information Network Exchange) work station, recently
announced by Datapoint Corporation, combines a camera and speakerphone with a
high-resolution-color video graphics display screen.
The MINX can be configured with Datapoint's Vista-PC or with the IBM PC, AT,
or XT, in which case the PC monitor is replaced by the MINX. A mode key on
the workstation permits the user to shift between the video communications
mode and the normal PC mode.
Another indication of this revolution is provided by Northern Telecom
(creators of DMS-100, 200, & 250), which recently added Meeting Communications
Services (MCS) to its Meridian DV-1 voice/data system. This option allows up
to 24 participants to conduct simultaneous audio communication and up to eight
participants to view, modify, and exchange data using Meridian M4000
integrated terminals.
A third and final example is the Luma phone from Luma Telecom. This device,
which uses regular phone lines, combines audio with black-and-white
freeze-frame video on a three-inch-diagonal screen. Strictly a telephone
product, the Luma phone has no computer features and will not transmit data.
For more information on the Luma phone, please see the November, 1986 issue of
The Sharper Image catalog.
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Videoconferencing is the way of the future and its only drawback is that of
economic cost. Increased use of videoconferencing will depend a lot on the
adoption of the Integrated Services Digital Network (ISDN), a standard,
all-digital communications service promised by the regional Bell Operating
Companies (BOCs).