203 lines
10 KiB
Plaintext
203 lines
10 KiB
Plaintext
==Phrack Inc.==
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Volume One, Issue Nine, Phile #8 of 10
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"Introduction to Videoconferencing"
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by Knight Lightning
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Written On 10/3/86
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Hi, KL here welcoming you to a look at Videoconferencing. This is a
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relatively new field that definitely bears investigation as videoconferencing
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is only a step away from everyone having video communication in the home. Well
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enough is enough, I hope you enjoy the file --KL.
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______________________________________________________________________________
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Despite the growing use of videoconferencing, confusion still exists regarding
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what it can and cannot do. This file should begin to help answer some of the
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questions about videoconferencing and perhaps formulate new ideas as well.
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Videoconferencing is not just one thing. It takes several different forms and
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can be designed in many different ways. Most of these ways are probably still
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waiting to be discovered.
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First of all, there are two main categories of videoconferencing. There is
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Point-to-Point and Point-to-Multipoint.
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Point-to-point/Two-Way Videoconferencing
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----------------------------------------
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Two-way videoconferencing enables people to conduct meetings even though the
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participants are in separate locations. Using interactive video and audio
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equipment, participants in one location can see, hear, and interact with
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colleagues in another location.
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The most familiar example occurs regularly on TV. When a newscaster in
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Washington interviews a head of state on the opposite side of the world
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"live," that's point-to-point, full-motion, full-color videoconferencing.
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Point-to-multipoint/One-Way Videoconferencing
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---------------------------------------------
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The one-way videoconference allows an organization to present video
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information to large audiences in multiple locations at the same time.
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One-way videoconferences are very different from two-way videoconferences in
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purpose and in implementation. Two-way videoconferences allow small groups in
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two, or possibly several, locations to interact audio-visually. In contrast,
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one-way videoconferences are designed to provide a one-way audio-visual
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presentation of information from an originating site to audiences at numerous
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receiving locations.
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The remote "audiences" are not seen by the initiators of the presentation.
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However, since both types of videoconferencing take place in real time, live,
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the audience can participate over the phone.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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There are two variations on the above listed categories of videoconferencing;
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Full-motion videoconferencing and freeze-frame videoconferencing. Each
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carries its own set of system requirements and each accomplishes quite
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different tasks.
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FULL-MOTION Videoconferencing
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-----------------------------
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Full-motion videoconferencing is like watching television. You can see
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participants in another location in color and in "real time" motion. You can
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identify who is present (provided that they are within camera range) and who
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is speaking. You can see facial expressions, hand gestures, and general body
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language. Motion video is used primarily for images of people.
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Motion Transmission On Wideband Channels
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----------------------------------------
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There is far more information in moving pictures then in a still image.
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Consequently, the size of the communications channel required to transmit and
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receive motion is far greater than that required for a still image.
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Transmission of a television signal in its original analog form (as it would
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come from a TV camera), requires terrestrial television channels or a
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satellite transponder. Terrestrial television channels are not readily
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available for occasional corporate use; satellite transponders are available.
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Most systems therefore, incorporate digital compression techniques to reduce
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the bandwidth required for motion videoconferences. Example: An image in
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motion is refreshed on a television screen 30 times per second. This means
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that the bandwidth necessary to transmit the image is very high, usually 1.5
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megabits per second (Mbps).
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This bandwidth is beyond the capacity of the standard telephone cable. A
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device called a "codec" digitizes the analog television signal and compresses
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it by eliminating redundant information. Currently, codecs can reduce the
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bandwidth to 56 kilobits per second (Kbps) and it is hoped that this bandwidth
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can be compressed even further.
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The resulting signal can be transmitted over less than full bandwidth
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channels. The picture is of somewhat less quality than the original analog
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image, but more than sufficient for most meetings.
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FREEZE-FRAME Videoconferencing
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------------------------------
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Freeze-frame videoconferencing is like a slide show. It captures still images
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either in color or black-and-white. Freeze-frame "stills" of people seem
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unnatural and can be distracting. Yet, freeze-frame video is best for still
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images of three-dimensional objects such as a product or a part, and for
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charts, drawings, graphics, and specially prepared presentation material.
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Freeze-Frame Transmission On Narrow Band Channels
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A freeze-frame system captures an image by stopping, or freezing any motion
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that might be present. The image can be transmitted via analog or digital
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signals over narrow channels. These channels are considerably narrower than
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those used for full-motion video conferencing. In its simplest form,
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freeze-frame video can utilize ordinary telephone line transmission. A single
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freeze-frame image will require at least 30 seconds to a minute or more for
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transmission.
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In some systems, the freeze-frame image is displayed line by line as it is
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received. This creates a vertical "waterfall" effect or a horizontal scanning
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effect. In other systems, the incoming lines of picture information are
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stored in a buffer until the completed picture can be displayed as a whole.
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In still other systems, an image emerges in successively better resolution as
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additional picture information is received.
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Enhancements To Freeze-Frame Video Systems
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There are a number of ways to expand a freeze-frame video system's
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capabilities. One enhancement is telewriting. With a "pen" connected to a
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telewriting device, users can point out a portion of a freeze-frame video
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image, overlaying lines and markings in various colors that are displayed at
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all locations as they are drawn. Some telewriting devices include stored
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geometric shapes, logos, and symbols that can be transmitted as overlays to a
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freeze-frame image. Zoom capability enables close-up analysis of portions of
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a display.
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Personal Computers and Desktop Videoconferencing
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Personal computers are beginning to be increasingly used with freeze-frame
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videoconferencing. PCs are used for control, for the creation of graphics,
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and for storage and retrieval of graphics material. There are signs that this
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evolution towards desktop videoconferencing has already begun.
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The MINX (Multimedia Information Network Exchange) work station, recently
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announced by Datapoint Corporation, combines a camera and speakerphone with a
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high-resolution-color video graphics display screen.
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The MINX can be configured with Datapoint's Vista-PC or with the IBM PC, AT,
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or XT, in which case the PC monitor is replaced by the MINX. A mode key on
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the workstation permits the user to shift between the video communications
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mode and the normal PC mode.
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Another indication of this revolution is provided by Northern Telecom
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(creators of DMS-100, 200, & 250), which recently added Meeting Communications
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Services (MCS) to its Meridian DV-1 voice/data system. This option allows up
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to 24 participants to conduct simultaneous audio communication and up to eight
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participants to view, modify, and exchange data using Meridian M4000
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integrated terminals.
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A third and final example is the Luma phone from Luma Telecom. This device,
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which uses regular phone lines, combines audio with black-and-white
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freeze-frame video on a three-inch-diagonal screen. Strictly a telephone
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product, the Luma phone has no computer features and will not transmit data.
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For more information on the Luma phone, please see the November, 1986 issue of
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The Sharper Image catalog.
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Videoconferencing is the way of the future and its only drawback is that of
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economic cost. Increased use of videoconferencing will depend a lot on the
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adoption of the Integrated Services Digital Network (ISDN), a standard,
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all-digital communications service promised by the regional Bell Operating
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Companies (BOCs).
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ISDN will offer users 144 Kbs or more which can be allocated among various
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communications tasks--data, voice, or video--in whatever proportion is
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necessary. This means that the available bandwidth could support simultaneous
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audio and video communication.
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______________________________________________________________________________
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References:
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----------
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"Electronic Meetings: Substitutes With Substance?," by Sam Dickey, Today's
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Office, July 1986.
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"Getting The Full Picture On Corporate Videoconferencing," by Marita Thomas,
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Facilities Design & Management, June 1986.
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"The Lid Is Off ISDN," Tomorrow's Communication Connection, April 1986.
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"Videoconferencing; An Alternative Solution," Corporate Informations Systems,
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General Electric (GE).
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______________________________________________________________________________
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Onto the next generation... --KL
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