Video Conferencing Glossary, a simple guide to videoconferencing and associated terms.

Voice only connection of more than two sites using standard telephone lines.

Audio Bridge
A device used in audioconferencing that connects multiple telephone lines.

In casual use the amount of information that can be transmitted in an information channel. High bandwidth Internet access means that web graphics load quickly on Netscape. High bandwidth videoconferencing means that the picture and the sound will be clear. In computers, the speed at which data can be transmitted on a communications frequency. In telecommunication, the maximum frequency (spectrum) measured in Hertz or cycles per second, between the two limiting frequencies of a channel.
128kbs, 256kbs, 384kbs, 512kbs, 768kbs Kbs or kbps means kilobyte per second. The numbers indicate the connection speed or bandwidth that a facility’s equipment is capable of supporting. To increase the quality of a video conference, you need to increase the bandwidth.

B channel
The ISDN circuit-switched bearer channels, capable of transmitting 64 Kbps of digitized information.

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)

A high capacity communications circuit or path. It usually implies a speed greater than 1.544 Mbps. (Contrast with wideband and narrowband).

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.

Certified Firewalls
Since H.323-compliant applications use dynamically allocated sockets for audio, video and data channels, a firewall must be able to allow H.323 traffic through on an intelligent basis. The firewall must be either H.323-enabled with an H.323 proxy, or able to “snoop” to control channel to determine which dynamic sockets are in use for H.323 sessions and allow traffic as long as the control channel is active.

An acronym for Coder / DECoder.
In short, a codec is a piece of hardware or software that takes some signal (such as video or audio) and converts it to a format suitable for transportation using a specific set of protocols. Equipment on the receiving end must also use these same protocols. The H.323 standard is a collection of protocols designed to ensure compatibility between products of various manufacturers. Even though the term “codec” specifically refers to the hardware or software converter the term has come to include the entire set of video conferencing terminal equipment. Someone saying “codec” is most likely referring to a set of terminal equipment. The terms “video conferencing terminal” and “codec” are used interchangeably.

Compressed video
When the vast amount of information in a normal 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. Some information is sacrificed in the process, which may result in diminished picture and sound quality.

DNS Name
The domain name system (DNS) is the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember “handle” for an Internet address.

Desktop videoconferencing
Videoconferencing on a personal computer. Most appropriate for small groups or individuals (compared with room-based videoconferencing). Many desktop videoconferencing systems support document sharing.

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.

Document Camera
The equivalent of an overhead projector. Images of two or three dimensional objects using either top or base lighting can be transmitted to remote sites when this video source is selected.

The process of eliminating acoustic echo in a videoconferencing room.

A firewall is a set of related programs located at a network gateway server that protects the resources of a private network from users from other networks. (The term also implies the security policy that is used with the programs.) An enterprise with an intranet that allows its workers access to the wider Internet installs a firewall to prevent outsiders from accessing its own private data resources and for controlling what outside resources its own users have access to.

Full Duplex
Sending data in both directions simultaneously “bidirectional” with a higher quality. In video conferencing full duplex will be much more natural and useable. Cheap speakerphones are half duplex, whereas more expensive ones are full duplex.

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.

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, images are sent in real time and motion is continuous..

The gatekeeper is the brain of an H.323 network performing essential control, administrative, and managerial functions. However, the gatekeeper does not route any data packets in a network. These continue to rely on standard network routing equipment. The primary purposes of a gatekeeper are address translation and zone administration using layer three of the OSI model.

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. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company’s network or at your local Internet service provider (ISP) are gateway nodes. Can transcode or allow different protocols to talk to each other.

H.323 standard
The H.323 protocol is the International Telecommunications Union – Telecommunications (ITU-T) standard for real-time multimedia communications and conferencing over packet-based networks.

The ITU standard for video conferencing over digital networks such as ISDN.

The ITU standard for adaptation of H.320 video conferencing over digital networks such as B-ISDN.

The ITU standard for video conferencing over packet switched networks such as LANs and the Internet.

Hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions.

IP address
The IP address is usually expressed as four decimal numbers, each representing eight bits, separated by periods. This is sometimes known as the dot address and, more technically, as dotted quad notation. For Class A IP addresses, the numbers would represent “network.local.local.local”; for a Class C IP address, they would represent “” The number version of the IP address can (and usually is) represented by a name or series of names called the domain name.

Stands for Integrated Services Digital Network. ISDN is essentially a digital network that will provide seamless communications of voice, video, and text between individual desktop videoconferencing systems and group videoconferencing systems. ISDN is expected to replace current telephone lines.

An issue occasionally associated with videoconferencing over packet networks. Is caused when there is a variation in network latency, meaning that the image appears stuttered and doesn’t flow. Occurs when there is no guaranteed Quality of Service (QoS) during a videoconferencing call and results in loss of image and audio quality.

Kilobits per second. Refers to transmission speed of 1,000 bits per second.

Sometimes referred to as High latency. Associated with network problems and results in a loss of the syncronisation between audio and image.

The speed at which videoconferencing (audio and video) data takes to make the journey from sender to recipient.

Multipoint Conference Unit
The Multipoint Conference Unit (MCU) is an important part of any videoconferencing infrastructure, allowing three or more parties or persons to get together in a virtual meeting room.

Multipoint videoconference
Videoconference with more than two sites. The sites must connect via a video bridge. (Compare with point-to-point videoconference.)

Network Address Translation (NAT) is the translation of an Internet Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside. Typically, a company maps its local inside network addresses to one or more global outside IP addresses and unmaps the global IP addresses on incoming packets back into local IP addresses. This helps ensure security since each outgoing or incoming request must go through a translation process that also offers the opportunity to qualify or authenticate the request or match it to a previous request. NAT also conserves on the number of global IP addresses that a company needs and it lets the company use a single IP address in its communication with the world.

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 multipoint videoconference.)

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.

QoS (Quality of Service)
A term commonly used when referring to a network, its quality and its reliability. Quality of Service on a network will guarantee a good standard of call and a definite amount of bandwidth.

Subnet Mask
The subnet mask is used to determine where the network number in an IP address ends and the node number in an IP address begins. A node is anything on a network that needs an IP address to communicate (a PC, server, router, etc).

Standard compression algorithm
An algorithm convention for compression of a video signal. Adherence 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. H320 is the most widely accepted standard in use today.

Set-Top System
The term set-top system usually refers to a vendor’s mid-level product designed for small to medium sized conference rooms. This system can look just like the room system with monitors and carts, or it can be a smaller unit that sits on top of a monitor. These systems typically will perform the same as the room systems at lower data rates; however, the set-top systems typically do not support data rates above 768K and do not have the built-in multipoint conference capability. One advantage to the set-top solution is that products on the lower end of this pricing scale can give a user excellent conference room or classroom performance as long as they do not require the extra services or options offered by the room systems.

This is when a bridge enables different video conference systems to connect when they are not directly compatible. E.g. converting IP to ISDN, (also known as a gateway) or connecting two systems that don’t work directly.

Video bridge
Computerized switching system which allows multipoint videoconferencing.