A sequential problem-solving procedure. For example, a text compression algorithm can be as simple as removing all extra space characters, inserting a single repeat character to indicate a string of repeated characters, and substituting smaller bit strings for frequently occurring characters. This simple step-by-step process, or algorithm, can reduce a text file to 50% of its original size. The algorithm also determines how to decompress data.
Audio and video signals currently used in broadcasting are analog as are many telephone lines. The signal is represented represented by a continuous wave because the signal is constantly varying within a range as opposed to pulsed, discrete digital signals.
Generally, the amount of information that can be transmitted over an information channel. High bandwidth Internet access means those audio, video, and graphics load quickly. High bandwidth videoconferencing means picture and sound will be clear. In computers, bandwidth is 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.
Comes from binary digit. The smallest unit of information with 2 possible
states. Computers use a series of 1's and 0's called the binary system to work with data. All data is stored in binary code as 1's (1 means yes or on) and 0's (0 means no or off). There are eight bits in one byte.
bit/sec or b/s)
bits per second (lower case is significant) is a common measure of data speed for computer modems and transmission carrier signals. As the term implies, the speed in bps is equal to the number of bits transmitted or received each second. The bandwidth of a signal depends on the speed in bps. One kilobit per second (abbreviated Kbps in the U.S.; kbps elsewhere) is equal to 1,000 bps. One megabit per second (Mbps) is equal to 1,000,000 bps or 1,000 Kbps.
Telecommunication in which a wide band of frequencies is available to transmit information. Like a highway with more lanes, broadband is broken down into various channels which allow more data to travel over the line at the same time. There is controversy over what speed is considered broadband; some say a connection of 500kbps or more.
BRI ISDN (Basic Rate Interface)
Basic Rate Interface
or BRI ISDN converts your regular telephone wires into three signaling channels. Two 64 kilobit per second (Kbps) Bearer (B) channels each carry user information (voice and data), while one 16Kbps Data (D) channel carries call set-up and signaling information, giving you a maximum capability of 144Kbps. The D Channel also enables X.25 packet applications such as credit card authorizations, automatic teller machine transactions and other short bursty messages that would needlessly tie up a connection over the regular circuit-switched network. The 2 B channels can be combined in one call for such applications as videoconferencing for a total of dedicated 128Kbps bandwidth.
[Most high quality ISDN videoconferencing programs are done over 3 BRI lines for a total of 384Kbps].
Allow you to pre-define camera angles, locations, and distances and store them into a videoconferencing
are so simple to use that it's basically just four steps: 1) Use the remote or control to select a camera to set (Can include the remote camera at the other end of your call!);
2) Position the camera by using the arrow buttons and ZOOM control to the desired location and distance;
3) Press SELECT or whatever the command is; 4) Confirm selection. Often a number is assigned to the preset. During a videoconference, you need only press that preset number and the camera will automatically change to the location and distance you preset.
Cascading is a method of allowing the number of participants to expand beyond what a single MCU can support. Cascading allows one MCU videoconference to join or be invited into another MCU videoconference. The joining MCU videoconference becomes a participant of the videoconference it joins and is treated like the other participants. The host MCU sends the joining MCU the processed data streams, which the latter distributes to its videoconference participants. In this way, all of the participants in the expanded videoconference receive the same information.
chair control mode
In this standards-based mode (H.243), the "conference chair" determines which location(s) will be viewed by all the other locations, can add or drop sites, can change the chair, can end the call. This allows a moderator to maintain control when there are numerous participants. The endpoint that assumes Chair Control is called the Chair Endpoint. This mode is only supported as long as the endpoint equipment is H.243 standards compatible.
The complete path between two points or terminals over which one-way or two-way communications may be provided with capabilities for a number of channels. A simple dial-up connection is a circuit that is reserved only for the duration of the call. A dedicated circuit is reserved in advance or leased for a period of time and can only be used by the owner/renter.
codec (Coder-Decoder or Compression - Decompression)
Videoconferencing hardware uses a codec to code the outgoing
video and audio signals and decode 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.
Compression is the reduction in size of data in order to save space or transmission time. Transmission of compressed video
over a communications network requires sophisticated compression algorithms.
When the vast amount of information in a normal tv transmission 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 signal. Some information is sacrificed in the process, which may
result in diminished picture and sound quality. Some videoconferencing systems offer both proprietary and standard compression algorithms. You'll want to make sure that you know whether your system is proprietary or standard before you buy as this will limit the types of videoconferences in which you can participate.
The screen is split into quadrants and allows multiple sites to be viewed simultaneously on the same screen.
Videoconferencing on a personal computer. Most appropriate for small groups
or individuals (compare with room-based videoconferencing).
The windows operating system has included NetMeeting, a desktop videoconferencing software, for many years. Desktop videoconferencing systems support a variety of interactive activities including document
sharing, whiteboard use, and chat.
A feature supported by many systems that allows participants at both ends of a videoconference to view
and/or edit the same computer document. It's important to decide who has control over the document at any given time. At the end of the session, it is usually possible to transmit the document to videoconference participants.
In general, digital signals can be transmitted faster and more accurately
than analog signals. As an example, music from digital cd's is usuallu more
clear than music from analog records. (Contrast with analog
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.
Process of eliminating acoustic echo in a videoconferencing room. Automatically built-in most systems nowadays.
Standards-based formats for communicating between videoconferencing systems
from different vendors. QCIF is one quarter of the resolution of FCIF.
Many networks now have firewalls to protect internal data from internal and external hazards. In order to videoconference over an IP network with a firewall, ports are assigned to handle the video. H.323 specifies the dynamic ports within a specific range.
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 duplex audio
2-way audio simultaneously transmitted and received without any interference
or "clipping." A common feature of room-based videoconferencing systems. Contrast with half duplex audio.
full motion video
Full motion video is equivalent to broadcast television video with a frame
rate of 30 fps. Images are sent in real time and motion is continuous.
Gatekeeper software uses the H.323 standard. Basically, a gatekeeper registers information about users which then enables it to look-up users and connect them.
A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. In videoconferencing, a component (often a computer or dedicated server) that provides the protocol translation allowing H.323 endpoints, H.320 systems, and others to participate in the same videoconference.
An advanced feature that is increasingly being used to control multipoint videoconferences. See Chair Control mode.
A widely-used video compression standard that allows
a wide variety of videoconferencing systems to communicate.
Usually associated with ISDN.
A rapidly growing video compression standard that allows
videoconferencing systems to communicate over the internet using IP.
A less popular standard that uses the regular POTS (plain old telephone service) to videoconference.
A relatively new video compression standard developed by the Internet2 Middleware Initiative Video Working Group and the Video Development Initiative (ViDE), that provides a "light directory access protocol" (LDAP) object class specification designed to store and locate information related to video and
over Internet Protocol (VoIP) in enterprise directories. H.350 supports H.320, H.323, session initiation protocol (SIP), and non-standard protocols including IP addresses, aliases and other connection related details. For more on this new standard, see the H.350 site developed by the Video Middleware working group.
half duplex audio
2-way audio transmitted and received in turn (rather than simultaneously)
so only one site can speak at a time. Contrast with full duplex
IP, internet protocol
Internet protocols are used to communicate across any set of interconnected networks. Internet protocols can be used to specify common applications such as electronic mail, terminal emulation, and file transfer. Internet protocols were first developed in the mid-1970s, when the Defense Advanced Research Projects Agency (DARPA) became interested in establishing a packet-switched network that would facilitate communication between dissimilar computer systems at research institutions.
Stands for Integrated Services Digital Network. ISDN is a high-quality, switched digital communications service that gives your standard phone line the ability to transmit voice and data simultaneously. You can use the same line for regular telephone service, faxing, computer communication, or even live videoconferences. Each of these applications requires suitably equipped customer-provided equipment. ISDN transmissions are significantly faster than using a modem.
Stands for Local Area Network. Most LANs are confined to a single building or group of buildings and connect workstations, printers, and other devices. LAN's enable to access data and devices anywhere on the LAN so that users can share equipment and data.
A system of connected LANs is called a wide-area network (WAN).
A listserv is an automatic e-mail server. People with similar interests "subscribe" to a given listserv for the purpose of discussion. Subscribers' contributions to the discussion are called "threads" are sent by e-mail to the entire subscriber list. LISTSERV refers to a specific mailing list server but, like Kleenex or Xerox, the term is sometimes used incorrectly to refer to all group e-mail servers.
The combination of two or more signals from two or more channels into a single output. For example, in ISDN, three BRI lines (6 channels) are normally used to create a single 384 kbps connection. This is the minimum standard speed for higher end videoconferencing. The multiple channels must be multiplexed or de-multiplexed with a Network Terminating (NT-1) device. These are usually built-in to videoconferencing systems.
multipoint control unit (MCU)
Also called a bridge, a component that manages videoconferences of three or more participants. An MCU can support some or all of the following: audio-only calls,
video calls at various video bandwidths,
video calls with T.120 data sharing, continuous presence, cascaded calls, conference call web page, and component stacking.
Videoconference with more than two sites. In the old days, sites had to connect via an MCU. Most high end units now have built-in MCUs which enable multipoint videoconferences as simply as dialing one site. (Compare with point-to-point videoconference.)
A low-capacity communications circuit/path. It usually implies a speed
of 56Kbps or less. (Contrast with wideband and broadband)
Standard for scanning television signals. Used in the U.S., Canada, and
Messages are divided into packets before they are sent. Each packet has a head and tail and is transmitted individually. Packets can even follow different routes to its final destination. Once all the packets arrive, they are recompiled into the original message.
Standard for scanning television signals. Used in most European countries.
A simple "map" which shows where various participants are sitting. This is very useful for meetings and small group activities. Many videoconferencing systems will allow you to transfer files during a videoconference, if so, consider exchanging participant maps if multiple sites are attending.
Videoconference between two sites. (Compare with multipoint
This mode, also called broadcast or lecture mode, enables a single location (the broadcaster or presenter) to be be viewed and heard continuously by all participants during the conference. Normally, switching among sites will not occur.
proprietary compression algorithm
A vendor-specific algorithm for compression of
a video signal. A videoconferencing system using a proprietary algorithm can
only communicate with a remote site using the same algorithm. Many vendors
also adhere to standard compression algorithms to
facilitate communication across platforms.
A standardized format for transmitting data between two devices. The protocol determines error checking, data compression, and the formal beginning and end of messages.
Videoconferencing service offered to the public on a fee-for-usage basis.
public switched telephone network (PSTN)
A domestic telecommunications network usually accessed by telephones, key telephone systems, private branch exchange trunks, and data arrangements. Note: Completion of the circuit between the call originator and call receiver in a PSTN requires network signaling in the form of dial pulses or multifrequency tones.
Videoconferencing using a large, sophisticated system. Appropriate for large groups
(compared to desktop videoconferencing).
standard compression algorithm
An algorithm convention for compression of a video
signal. Adherance to standards allows communication among a wide variety of
videoconferencing systems, though not with the same clarity as two similar
systems using a proprietary algorithm. H.320 and H.323 are the most widely accepted standards in use today. H.350 is
relatively new and probably on the rise.
Streaming media technology allows real time or on demand delivery of audio, video and multimedia. Digital media (video, voice, data) is received in a simultaneous, continuous stream. These applications can start displaying video immediately or play as soon as enough data has been received and stored in the receiving station’s buffer.
switched digital communications
Switched communications allow you, the user, to dial up any other user on the public network versus a dedicated point-to-point connection. Digita
A standard for realtime data conferencing (sharing data among multiple users). It defines interfaces for whiteboards, application viewing and application sharing. There are numerous breakdowns within the T.120 standard which handle specific functions such as multipoint service;
audiovisual protocol; generic conference control;
conference management (establish, terminate, etc.); network mappings; and reservation services.
Computerized switching system, properly called an MCU, which allows multipoint
Communication across long distances with video and audio contact that may
also include graphics and data exchange.
Voice-Activated Switching (VAS)
This is normally the default mode. When multiple sites are participating, the person currently speaking is viewed by all participants. The downside to this is that any noise, such as a person coughing or a phone ringing, will change the view. That is why it is important to mute when you are not planning on being the "main event." See also continuous presence.