Videoconference Glossary

Analog Transmission
The way information is transmitted over a continuously changing electrical wave that is similar to, or analogous with the original signal. All telephone calls used to be transmitted in an analog format. Today they are translated to digital pulses for both local and long-distance transmission. Your television at home receives analog signals.

ATM
Asynchronous Transfer Mode. A standard implementation of cell relay, which is a packet switching technique using packets (cells) of a fixed length. It is asynchronous in the sense that the recurrence of cells containing information from an individual is not periodic.

B-Channel
Bearer Channel. The fundamental component of an ISDN circuit, the Bearer Channel carries either voice or data at 64000 bits per second (64 kbps) in either direction.

Bandwidth
The effective carrying capacity of a telecommunications transmission medium. Bandwidth describes how much information can be pushed through an electronic "pipe" at any given time.

Bit Interleaving/Multiplexing
A process used in time division multiplexing where individual bits from different lower speed sources are combined (one bit, from one channel at a time) into one continuous higher speed bit stream.

BRI (Basic Rate Interface)
The ISDN standard that governs how phones and other electronic devices are connected to the ISDN switch.

Bridge
A videoconference bridge is usually made up of back-to-back codecs from different manufacturers to convert signals from one proprietary system to another.

Broadband
Digital services at rates greater than 1.536 million bits (mbps), capable of supporting voice, video, and data, possibly using multiple channels.

CCITT
Consultative Committee International for Telegraphy and Telephony. A European-based, international advisory committee recommending worldwide standards for transmission. This committee is now known as ITU.

Channel
A path for electrical transmission between two or more points. Also called a link, line, circuit, or facility.

Codec
An acronym for Coder/Decoder. This device compresses (for transmission) and decompresses (once received) digital video and analog audio signals so that they occupy less bandwidth during transmission.

Compression
Any of several techniques that reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory.

Continuous Presence
The transmission of two or more simultaneous images.

CSU
Channel Service Unit is a device that provides an interface between codecs and transmission facilities. It is usually equipped with line-conditioning and switched control capabilities.

D-Channel
The Data Channel on the ISDN circuit is used to carry control signals and customer call data at 16 kbps (BRI) and 64 kbps (PRI).

Data
Information represented in digital form, including voice, text, facsimile, and video.

DS-0
A 64 kbps channel.

DS-1
The Level 1 standard for digital systems operating at 1.536 mbps (24 DS-0 channels). Also known as T1.

DS-3
Digital Signal Level 3. This term is used to refer to the 45 mbps digital signal carried on a T3 facility.

DSU
Digital Service Unit. A user device for interfacing to a digital circuit such as DDS or T1 when combined with a CSU. The DSU converts the user's data stream to bipolar format for transmission.

Dedicated Access
A private connection between a customer's equipment and a company providing transmission services. The connection bypasses the local switched telephone network.

Dedicated Network
Sometimes referred to as a private or leased line. This transmission circuit is used exclusively by a single customer.

Digital Transmission
A way of sending coded information via a series of electric or light pulses through the air, over wires, or through glass fibers.

Echo Cancellation
A technique used in high-speed modems and voice circuits to isolate and filter out unwanted signal energy caused by echoes from the main transmitted signal.

FCIF
Full Common Intermediate Format describes the type of video format transmitted using TSS standard coding methods.

FPS
Frames Per Second.

Fractional T1
A service provided by carriers, where a full T1 link is leased to a customer, but the service charge is based only on the number of time slots used.

Full Duplex
A system capable of transmitting and receiving signals simultaneously.

Gbps
Gigabits per second. 1 Billion bits per second.

H.320
An international standard designed to bring interoperability to videoconferencing.

Half Duplex
A system capable of transmitting and receiving signals in one direction at a time.

Interoperability
A state of compatibility between videoconferencing units that may support differing levels of compatibility.

IP
Internet Protocol. Allows for videoconferencing over LAN or commercial Internet.

ISDN
Integrated Services Digital Network is an international standard for digital services on the public switched telephone network.

ITU
International Telecommunication Union. Formerly known as CCITT.

Jitter
The deviation of a transmission signal in time or phase. It can introduce errors and loss of synchronization in high-speed synchronous communications.

kbps
Kilobits per second. 1 Thousand bits per second.

LAN
Local Area Network. A high volume data transmission signal is returned to the sending device after passing through all or part of a communications link or network.

mbps
Megabits per second. 1 Million bits per second.

Multiplexer (MUX)
A device allowing two or more signals to pass over and share a common transmission path simultaneously.

Network
1. An interconnected group of nodes.
2. A series of points, nodes, or stations connected by communications channels; the collection of equipment through which connections are made between data stations.

Packet
An ordered group of data and control signals transmitted through a network as a subset of a larger message.

PBX
Private Branch Exchange.

Port
The physical interface to a computer multiplexer, for connection of terminals and modems.

PRI
Primary Rate Interface is the combined signal-carrying capacity of 23 B-Channels (Bearer Channels) operating at 64 kbps and one D-Channel (Data Channel) also functioning at 64 kbps. The total capacity is equal to that of 1 DS-1 circuit.

Protocol
A formal set of conventions governing the formatting and relative timing of message exchange between two communicating systems.

PSTN
Public Switched Telephone Network. The telecommunications network commonly accessed by ordinary telephones, key systems, PBX trunks, and data equipment.

SONET
Synchronous Optical Network. A standard for using optical media as the physical transport for high-speed, long-haul networks. SONET basic speeds start at 51.84 mbps and go as high as 2.5 Gbps.

Statistical Multiplexer (STM or STDM)
A device connecting multiple channels to a single link by dynamically allocating time slots to the channels based on their transmission activity.

T1
A Level 1 digital transmission system operating at 1.536 mbps. Also known as DS-1.

TSS
Telephony System Specification.

Voice Compression
The conversion of an analog voice signal into a digital signal using minimum bandwidth (16 kbps or less).

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