The High Cost of Videoconferencing

Rising transportation costs and the time-wasteful aspects of travel have focused corporate attention on expensive broadcast-quality videoconferencing systems. But video on the desktop remains a problem. Although many solutions are available, the combination of desktop video and telephony is sure to disappoint--unless users are willing to make hardware investments that represent an order-of-magnitude increase over traditional desktop peripherals. Serious videoconferencing requires dedicated compression components and general-purpose DSP (digital signal processors) to handle the audio and modem algorithms.

Multimedia authoring systems that compress and decompress 24-bit-color, full-screen video at 30 frames per second require relatively wide, within-platform data transfer channels and are not adaptable to telecommunicat ions applications. Teleconferencing systems must squeeze information into low-bandwidth POTS (plain old telephone system) lines. The bit stream weighs in at 18 Kbps even when images are small 160- by 120-pixel snapshots with 8-bit color (typically talking head shots), JPEG-compressed at a 35-to-1 ratio, and updated only four times per second (thus losing lip sync). Sun Microsystems published results stating that researchers "found no evidence that groups are more effective or efficient at solving problems or making decisions when they are connected through a video and audio link than when they use only an audio link."

Hence, in a desktop environment with an analog phone line, users will give up 90 percent of their communications bandwidth to information that adds, perhaps, 5 percent to the value of the communication. Most PC-based desktop videoconferencing vendors offer solutions that require costly, dedicated, high-bandwidth lines. This limits these products' market appeal.

Video has its streng th in group-to-group conferencing, where dedicated systems are used. It may offer advantages in long (more than 60 minutes) person-to-person conferencing, since video provides more of the feel of a face-to-face meeting. But for individual business communications, data conferencing is probably the best solution. Bandwidth utilization is more sensible; the information is more useful, and systems without video cost 50 percent to 90 percent less than those with video. Most important, data-conferencing solutions provide high-productivity communications on POTS lines.

The present market attention on PC-based video for multimedia recording, playback, and desktop videoconferencing is misleading. The Apple Quadra 840AV and recent Windows-based machines announced by Acer America and NCR (now AT&T Global Information Solutions/NCR) lend insight into why. Customers generally applaud the Macintosh's sound capabilities but often describe the video as small, grainy, and too slow. Apple, in fact, has focused attention on the machines' new GeoPort telecommunications architecture, a software-based fax/voice/modem running on the motherboard's DSP3210 coprocessor.

Acer and NCR also recognize the limitations of video. They introduced computers with separate dedicated DSP subsystems for videoconferencing functions (which are based on AT&T's AVP 4000 chip set) and general-purpose DSPs for sound, audio, and telecommunications. The Acer motherboard includes two DSP3207s to support the bandwidth required for sound encoding and decoding, sampled synthesis, and echo cancellation, as well as modem, fax, voice coding, and telephone functions. AT&T's VCOS operating system supports multiple DSPs via a utility that balances compute tasks and I/O lines across DSP resources. The NCR architecture is similar, except that the general-purpose DSP for audio/modem and the dedicated ICs for video compression/decompression are on separate add-in boards, not the motherboard.

The Acer and NCR configurations are reflective not only of the compute horsepower needed for videoconferencing on the desktop but of the bandwidth requirements as well--both require ISDN connections. The question that begs an answer is, Why not just use data conferencing--videoconferencing without the video?

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Video Bandwidth Requirements

Image resolution, pixel depth, compression, and the number of frames transmitted per second all affect bandwidth requirements.


HORIZONTAL    VERTICAL                   FRAMES
RESOLUTION    RESOLUTION     PIXEL       PER         COMPRESSION
(PIXELS)      (PIXELS)       DEPTH       SECOND          RATIO
640            480           24            30              1
640            480            8            30              1
320            240            8            10              1
320            240            8            10             16
320            240            8            24            120
160            120            8             5             10
352            288            8
             2             30
352            288            8            10            200
320            240            8            10            200
120            100            8             2             10
160            120            8             4             35
352            288            8             2            120


COMPRESSION        RESOLUTION            RATIO TO V.32BIS
METHOD             BANDWIDTH (KBPS)      (19.2 KBPS)
None               221,184               11,520.00
None                73,728                 3840.00
None                  6144                  320.00
JPEG                   384                   20.00
Indeo                  123                    6.40
JPEG                    77                    4.00
JPEG                    54                    2.80
MPEG                    41                    2.10
MPEG                    31                    1.60
JPEG                    19                    1.00
JPEG                    18
                    0.90
Indeo                   14                    0.70