Glossary

Definitions of common terms in video conferencing

  • ADSL
    Asymmetric Digital Subscriber Line
    A data communications technology. Enables fast data transmission over copper telephone lines. Common in residential premises.
    Termed asymmetric because bandwidth for download is greater than for upload. Typically only the download speed is quoted but It is important to know both if it is used for video conferencing.
  • bandwidth
    The capacity of a network to transmit data - video and audio. The greater the bandwidth the better the quality of the picture being transmitted.
    Measured in thousands of bits per second (kbps) or millions of bits per second (Mbps).
  • BRI
    Basic Rate Interface
    An ISDN connection utilizing two 64Kbps B channels (bearer) and a single 16Kbps D Channel (Delta).
  • bridge
    see MCU
  • broadband
    A way of transmitting large amounts of data, voice, and video that is greater than telephony networks. In ISDN, broadband channels support rates above the primary rate (1.544 Mbps or 2.048 Mbps).
  • codec
    Coder-Decoder
    The primary hardware device or software application used in video conferencing. Used to code the outgoing video and audio signals and decode the incoming signals.
  • continuous presence
    A common feature in multipoint video conferences. Allows you to view multiple participants on one screen at the same time. This is an alternative to voice activated mode.
  • data sharing

    The simultaneous sharing of a document or application across a network or via a video conference.

  • desktop video conferencing
    Video conferencing from your desk using either a dedicated hardware device or software on your PC. Many desktop video conferencing systems support data / document sharing.
  • DNS
    Domain Name Server
    On TCP/IP networks, DNS converts the domain name (URL) of a host computer into a numeric IP address using the following format: xxx.xxx.xxx.xxx.
  • document sharing
    A feature supported by many videoconferencing systems that allows participants of a videoconference to view the same computer document.
  • DSL
    Digital Subscriber Line
    A way to transfer data over regular phone lines and connect to the Internet. Uses copper wires but is much faster than a regular phone connection.
  • echo cancellation
    Process of eliminating acoustic echo effect on videoconference calls. Automatically built-in most systems.
  • endpoint
    Typically refers to a codec. Technically can be any device at the end of a network such as PC, IP phone or codec.
  • far end
    The location where other participants of the video conference are located.
  • firewall
    A barrier between two networks. Can be a hardware or software based system. Filters network traffic to protect data from external hazards based on a set of rules.
    For video conferencing over an IP network with a firewall, specific ports may need to be opened.
  • firewall traversal
    Firewall traversal technology creates a secure path through the firewall barrier safely and seamlessly.
  • frame rate
    Described as frames-per-second (fps). Measures the frequency at which video frames are displayed on a screen. Higher rates improve the appearance of motion. Broadcast TV is 30 fps.
  • full duplex audio
    2-way audio simultaneously transmitted and received without any interference or "clipping." Contrast with half duplex audio
  • gatekeeper
    A management tool for H.323 multimedia networks. It can control access to the network and control the bandwidth of a call. It can also register information about users which then enables it to look-up users and connect them.
  • gateway
    A network point needed to gaining entrance to incompatible networks. Used for example when connecting H.323 standards based videoconferencing systems to non-compliant video conferencing systems.
  • H.261 / H.263
    ITU standard for video coding within video conferencing. H.263 offers better compression than H.261.
  • H.264
    The ITU-T standard for compression that allows higher quality calls to pass over a lower bandwidth for advanced video coding in generic audiovisual services.
  • H.320
    A commonly used ITU-T video compression standard for video conferencing over networks that provide fixed communication paths (such as the ISDN phone network).
  • H.323
    The most widely used current standard for video compression for video conferencing. It allows a wide variety of video conferencing systems to communicate over the internet using IP.
  • 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 audio.
  • interactive whiteboard
    a whiteboard linked to a computer to capture writing and drawing digitally.
  • inter - operability
    the capability of different video conference systems to talk to one another.
  • IP
    Internet Protocol
    A general term for the technologies that enable internet connections to exchange voice, video and other forms of information.
    IP often refers to a high quality broadband connection that is used to connect video conferencing systems.
  • IP address
    A unique identifier for each device on a network. Is 32 bits long and is divided into four 8-bit parts, each separated by a period, as in 149.122.3.30.
  • ISDN
    Integrated Services Digital Network.
    Refers to digital telephone lines. These allow both data and voice communications over the same line. ISDN replaced the analog local loop. Traditionally most video conferences were connected using an ISDN connection. Typically higher cost and lower bandwidth than IP.
  • ITU
    International Telecommunications Union
    The primary telecom standards setting organization. The ITU-T is the Telecommunication Standardization Sector of the ITU, developing standards for interconnecting telecommunication equipment across networks.
  • latency
    A measure of the delay in data passing over a network. Critical in video conferencing as it easily noticable from the quality of the ‘lip-sync’ - the lips moving in time to the audio.
  • leased line
    A dedicated telecommunications link between two predetermined points. Provides for voice, data and Internet traffic. Possible to control for example, QoS, bandwith allocation and connection speed.
  • MCU
    Multipoint Control Unit
    A device that connects three or more video conference sites so they can communicate. May also provide access to a web-based video conferencing application.
    Can be a separate hardware unit or embedded into a video conference codec.
  • multiplexing
    The combination of two or more signals from two or more channels into a single output allowing a number of simultaneous transmissions over a single circuit.
  • multipoint
    A video conference with more than two sites. Requires an MCU.
  • near end
    Your location on a video conference call.
  • packet
    A formatted unit of data carried by a computer network.
  • packet loss
    The discarding of data packets in a network when a device is overloaded and cannot accept incoming data at a given moment.
  • PRI
    Primary Rate Interface
    An ISDN connection utilising 23 64Kbps B channels (bearer) and a single 16Kbps D Channel (Delta). Also commonly called a T1.
  • protocol
    A standardized format for transmitting data between two devices. The protocol determines error checking, data compression, and the formal beginning and end of messages.
  • QoS
    Quality of Service
    The ability to define a level of performance in a data communications system.
  • SDSL
    Symmetric Digital Subscriber Line
    A data communications technology. It provides the same bandwidth rates upstream and downstream. It is the opposite of ADSL.
  • SIP
    Session Initiation Protocol
    An IP telephony signaling protocol that is suitable for integrated voice-data applications.
  • standards
    Rules for writing protocols so that different systems can connect with each other. Relevant standards for video conferencing include H264, H320 and H323.
  • streaming
    Video conference streaming is the broadcasting of a conference to remote participants over the internet.
  • SVC
    Scaleable Video Coding
    H.264 SVC is a compression standard that enables video conferencing systems to achieve highly error resilient IP video transmission over the public Internet without quality of service enhanced lines.
  • tele conference
    Two or more people who are geographically distant having a meeting across a telecommunications link. Includes audio conferencing, video conferencing, and or data conferencing.
  • telepresence
    High quality video conferencing. Often refers to dedicated rooms that are designed to specific standards that give the impression the far end participants are sitting across the same table.
  • transcoding
    performed by a gateway to enable different video conference systems to connect when they are not directly compatible, e.g. converting IP to ISDN.
  • unified communications
    Integration of real time communication technologies including video conferencing, IP telephony and instant messaging with non-real time communications such as email, SMS and fax.
  • video conference
    Using communication technologies to enable two or more people to see and hear one another when they are in different locations. It also allows the sharing of computer applications e.g. presentations and documents.
    Systems typically consist of a camera, codec, microphone, speakers and screen.
  • VAS
    Voice Activated Switching
    A feature of multipoint video conferences where the participating sites all see only the site which has last spoken. If someone from a different location speaks the view will then be of that site.
  • web conference
    Web conferencing is used to conduct live meetings, training, or presentations via the internet. Primary focus is document sharing. Low quality video may be provided too.