algorithm
A step-by-step problem-solving procedure. Transmission of compressed video over a communications network requires sophisticated compression algorithms. Some videoconferencing systems offer both proprietary and standard compression algorithms.
analog signals
Audio/video signals currently used in broadcasting where the signal is represented by variable measurable physical quantities (such as voltage). Current TV and radio signals are analog, as are many telephone lines. (Contrast with digital). Example devices: video camera, VCR, projector, scan converter, document camera, sound system.
audio
In video communications, electrical signals that carry sounds. The term is also used to describe systems concerned with sound with recording and transmission; speech pickup systems, transmission links that carry sounds, amplifiers and the like. Example devices: microphones, audio mixer.
audio bridge
Equipment that mixes multiple audio inputs and feeds back composite audio to each station after removing the individual station's input.
bandwidth
In casual use, the amount of information that can be transmitted in an information channel. High bandwidth Internet access means those web graphics load quickly on Netscape. High bandwidth videoconferencing means that the picture and sound will be clear. In computers, the speed at which data can be transmitted on a communications frequency. In telecommunications, the maximum frequency (spectrum) measured in Hertz or cycles per second, between the two limiting frequencies of a channel.
B channel
The ISDN circuit-switched bearer channels, capable of transmitting 64 Kbps of digitized information.
bps
Bits per second, a unit of measurement of the speed of data transmission and thus of bandwidth (lower case is significant).
Bps or BPS
(8-bit) bytes per second (upper case is significant)
BRI - Basic Rate Interface (ISDN)
3 digital signals over a single pair of copper wires: 2 voice (B) channels and 1 signal (D) channel. (e.g. voice and fax on a single pair of wires)
bridge
In videoconferencing vernacular, a bridge connects three or more conference sites so that they can simultaneously communicate. Bridges are often called MCU's - multipoint conferencing units. In IEEE 802 parlance, a bridge is a device that interconnects LAN's or LAN segments at the data-link layer of the OSI model to extend the LAN environment physically. They work with frames (as opposed to packets) of data, forwarding them between networks. They learn station addresses and they resolve problems with loops in the topology by participating in the spanning tree algorithm. Finally, the term bridge can be used in audio conferencing to refer to a device that connects multiple (more than two) voice calls so that all participants can hear and be heard.
carrier
A term used to refer to various telephone companies that provide local, long distance or value added services; alternately, a system or systems whereby many channels of electrical information can be carried over a single transmission path. Example carriers: AT&T, MCI, Sprint.
codec
Coder-Decoder. Videoconferencing hardware that codes the outgoing video and audio signals and decodes the incoming signals. Prior to transmission, the codec converts analog signals to digital signals and compresses the digital signals. Incoming audio and video must be decompressed and converted from digital back to analog.
compressed video
When the vast amount of information in a normal TV transmission (90 Mbps) is squeezed into a fraction of its former bandwidth by a codec, the resulting compressed video can be transmitted more economically over a smaller carrier (ISDN). Some information is sacrificed in the process, which may result in diminished picture and sound quality.
desktop videoconferencing
Videoconferencing on a personal computer is most appropriate for small groups or individuals (compare with room-based videoconferencing). Many desktop videoconferencing systems support document sharing.
digital signals
Audio/video signals represented by discrete variations (in voltage, frequency, amplitude, location, etc.). A digital clock, for example, displays the time as discrete numeric values rather than angular displacement of analog hands. In general, digital signals can be transmitted faster and more accurately than analog signals. As an example, music from digital cd's is usually more clear than music from analog records. (Contrast with analog signals.)
document sharing
A feature supported by many desktop videoconferencing systems that allows participants at both ends of a videoconference to view and edit the same computer document.
frame rate
Frequency in which video frames are displayed on a monitor, typically described in frames-per-second (fps). Higher frame rates improve the appearance of video motion. Broadcast TV (full motion video) is 30 frames-per-second.
full-motion video
Video reproduction at 30 frames per second (fps) for NTSC signals or 25 fps for PAL signals. Also known as continuous-motion video. In the videoconferencing world, the term "full-motion video" is often used, and often misunderstood. Videoconferencing systems cannot provide 30 fps for all resolutions at all times nor is that rate always needed for a high-quality, satisfying video image. Picture quality must sometimes be sacrificed to achieve interactive visual communication across the telephone network economically. Videoconferencing vendors often use "full-motion video" to refer to any system that isn't still-frame. Most videoconferencing systems today run 10 to 15 frames per second at 112 Kbps. Need 384 Kbps in order to transmit 30 FPS.
H.320 standard
A widely-used video compression standard that allows a wide variety of videoconferencing systems to communicate utilizing ISDN telephone lines.
H.323 standard
A widely-used video compression standard that allows a wide variety of videoconferencing systems to communicate utilizing IP (Internet Protocol).
ISDN - Integrated Services Digital Network
A CCITT standard for integrated transmission of voice, video and data. Bandwidths include: Basic Rate Interface - BR (144 Kbps - 2 B & 1 D channel) and Primary Rate - PRI (1.544 and 2.048 Mbps).
Integrated Services Digital Network. A set of protocol and interface standards that effectively constitute an integrated (voice, video, and data) telephone "network." These standards promote global availability and compatibility of ISDN products and services. The two types of ISDN discussed in this Guide are Basic Rate Interface (BRI) and Primate Rate Interface (PRI). ISDN BRI (ISDN Basic Rate Interface) is the interface to connect the desktop to the digital long distance network. ISDN BRI provides two 64Kbps B ("bearer") channels to carry information content, the voice, video, and data substance of a transmission. A separate 16Kbps D ("data") channel is used for call setup and signaling. ISDN BRI is often called "2B+D" ISDN, for its combination of two B and one D channel. This service is marketed and supported by the LECs. ISDN PRI (Primary Rate Interface) is the ISDN equivalent of a T-1 circuit. It provides 23B+D (in North America) or 30B+D (in Europe) running at 1.544 Mbps and 2.048Mps, respectively. Each channel (time slot) is 64Kbps. One channel is reserved as the D channel; the other 23, as bearer channels (23+D).
Kbps
Kilobits per second. Refers to transmission speed of 1,000 bits per second.
multi-point videoconference
Videoconference with more than two sites. The sites must connect via a video bridge. (Compare with point-to-point videoconference.)
NT 1
Network Termination type 1. The NT-1 is a device which converts the two-wire line (or "U" interface) coming from your telephone company into a 4-wire line (or "S/T" interface). The NT- 1 is physically connected between the ISDN board of your videoconferencing system and your ISDN phone line. The NT- 1 supports network maintenance functions such as loop testing. Check to see if your ISDN equipment requires an external NT-1 to operate.
NTSC - National Television Standards Committee (Never Twice the Same Color)
A video standard established by the United States (RCA/NBC} and adopted by numerous other countries. This is a 525-line video with 3.58-MHz chroma subcarrier and 60 cycles per second. Frames are displayed at 30 frames per second.
PAL - Phase Alternative Line System
The European TV standard based upon 50 cycles.per second electrical system and 625 lines per frame and 25 Frames per Second. (NTSC, the North American standard is based on 30 frames per second) (French use SECAM)
point-to-point videoconference
Videoconference between two sites. (Compare with multi-point videoconference.)
POTS
Plain Old Telephone Service. Conventional analog telephone lines using twisted-pair copper wire. This is used to provide residential service.
public room
Videoconferencing service offered to the public on a fee-for-usage basis.
room-based videoconferencing
Videoconferencing using a sophisticated system is appropriate for large groups. (Compare to desktop videoconferencing.)
room coordinator
A room coordinator (room monitor) is there to make sure the equipment is on and operational, greet the incoming attendees and be nearby in case something is needed i.e. adjust the volume, troubleshoot, indicate where the closest rest room is! They are not necessarily present in the room during the actual videoconference.
Switched 56
Switched 56 service allows customers to dial up and transmit digital information up to 56,000 bits per second in much the same way that they dial up an analog telephone call. The service is billed like a voice line-a monthly charge plus a cost for each minute of usage. Nearly all LECs and IXCs offer switched 56 service and any switched 56 offering can connect with any other offering, regardless of which carrier offers the service.
T-1
The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.
TELCO
Generic term for the local telephone company. Can refer to an Interexchange Carrier or to the Local Exchange Carrier.
whiteboarding
A term used to describe the placement of shared documents on an on-screen "shared notebook" or "whiteboard." Desktop videoconferencing software includes "snapshot" tools that enable you to capture entire windows or portions of windows and place them on the whiteboard. You can also use familiar Windows operations (cut and paste) to put snapshots on the whiteboard. You work with familiar tools to mark up the electronic whiteboard much like you do with a traditional wall mounted board.
videoconferencing
Communication across long distances with video and audio contact that may also include graphics and data exchange.
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