Your spouse faxes grocery lists from home to your office. You send bad jokes all over the world via e-mail. You buy books and wine over the Internet every week. You sit in on videoconferences with the advertising agency. You've got this high-tech communications thing wired, right? So why do you get this creeping cube of cold dread in your belly when the VP of engineering calls you up and demands a four-site, multipoint H.320 in directed mode . . . from Penang, Malaysia. Relax! You have all the essentials to communicate with any buzzword-barking engineer! Geek Speak is here to fill in the details so that you can confidently assure the VP that high-speed ISDN service out of Penang is no problem and by the way, has he considered a continuous presence call? Here's part two of the Digital Dictionary:
30fps: 30 frames per second. Just about TV broadcast quality, and a very satisfying experience. Many older videoconferencing systems top out at 20fps or so, with 30fps a pricey option. Newer ones come with 30fps standard and, following the peculiar economics of electronics, cost a lot less.
Algorithms, Compression: Any of several programs that squeeze the audio and video content of a transmission into the available bandwidth. May be standards-based or proprietary. Videoconferencing standards are defined by the International Telecommunication Union (ITU) and are usually identified by the letter H, followed by three digits (see H.320, 321, and 323 below). A proprietary algorithm can only be used by its manufacturer's systems, like system to like system (see SG-3 and SG-4 below). Systems equipped with proprietary algorithms also support standards-based transmissions.
Continuous Presence: A class of multi-point call that divides your monitor into four quadrants, each with a different leg of the call shown simultaneously. With your end either off-screen or on a slave monitor, you then get what feels a lot like five people, or ends, sitting around the same room. Tough to demo because four remote sites are needed.
Dial-Up vs. Satellite: Dial-up videoconferencing, usually over ISDN telephone lines, allows two-way, fully-interactive discussions between any number of people. Satellite broadcast videoconferencing is a one-way medium. This series is mainly concerned with dial-up videoconferencing.
Directed: A class of multi-point calls where the individual bridge operator (see multi-point control unit below) can direct signals from one end to all the other ends. You had better give the bridge a good script if you want a directed call's reality to match your vision.
H.320: The ITU standard for ISDN digital dial-up videoconferencing compression. Implies circuit-switched communication. If a vendor tells you its system fully supports the H.320 standard, then it should work with any other H.320 compatible system. It might work better with the same vendor's equipment. They're funny that way.
H.323: The ITU standard for Internet Protocol (IP) digital videoconferencing compression. This is an example of packet-switched communication. Gateway products are now in the marketplace allowing H.320 and H.323 systems to share network and codec resources.
Multi-point Call: Refers to a videoconference involving more than two ends. Requires a multipoint control unit. (See also Continuous Presence, Voice Activated, and Directed calls.)
Multi-point Control Unit (MCU): The MCU, aka the bridge. Can either originate calls, receive them, or mix them up. There is no limit to the number of ends you can bring into a call--although as you bring sites in, costs go up and interactivity goes down. It's possible to have dissimilar calls come into the same bridge, but expect some degradation if you bring a 128k end into a 384k call.
The bridge operator is a very important part of a multi-point call. Most do scheduling and room-brokering as well.
Network: Videospeak slang meaning "How is this call going, over ISDN, POTS or IP?"
Point-to-Point: A basic videoconference call involving only two ends.
SG-3, SG-4: Examples of proprietary compression algorithms that only work with like systems.
Systems, Desktop: Cute little cameras on top of your PC that put a cute little postage stamp of your face on the other guy's computer monitor, usually at low bandwidth.
System, Roll-About: A videoconferencing system on a cart that you can roll from room to room. Allows you to suit the venue to the size and type of event. It also lets you store the box in a closet instead the meeting room.
System, Room: Refers to a system in a dedicated facility built for videoconferencing.
Voice-Activated: A class of multi-point call that allows the bridge to automatically show to all sites the video signal coming from the site that is currently producing the most audio. In other words, the squeaky wheel gets seen.