Glossary of Term
A
auto-tracking
Feature of a Pan/Tilt/Zoom camera that enables it to follow a speaker either by voice detection (usual), by a colour pattern recognition or by Radio signals (rare). Helps to allow the speaker to move freely during a videoconference.
B
bandwidth
A measure of the amount of data that can fit on a network. Measured in Hertz or bits per second. For example, a regular Ethernet line has a bandwidth of 1000Mbps (1000 million bits per second.) Note that bandwidth is sometimes measured as the bandwidth in one direction, and sometimes as the total in both directions. Be sure you understand which it is for the system you are looking at.
bit rate
The number of data bits per second that can flow in a communications circuit.
Some common speeds are 56K (for dial up modems), 384K (for most entry level video conferencing) and 10 Megabits (for a low-speed Ethernet).
buffering
The process by which a codec stores temporarily captured video frames before encoding or decoding them in order to ensure regular and timely transmission or reception. In video conferencing, buffering is very limited, since communications must take place in almost real-time, which allows for delays of only a fraction of a second.
C
CODEC
Stands for Coder/Decoder (a telecommunications term) or Compressor/Decompressor (a computer term). A codec is a piece of hardware or software that compresses and decompresses digital audio and/or video. CODEC's reduce the amount of bandwidth needed for video conferencing.
D
decoder
A piece of hardware or software that is used to convert video or audio (typically) from the digital form used in transmission or storage into a form that can be viewed.
digital audio
Audio that has been encoded in a digital form for processing, storage or transmission.
E
echo suppression
Echo suppression is a crucial portion of all video conferencing systems. If echo is not suppressed, the speaker hears his own audio coming back from the other end of the circuit, after a small time delay. The fault always lies with the far end, although they do not perceive any problem.
F
firewall
A hardware or software based system that filters network traffic based on a set of rules. Simple firewalls normally block access to specific ports and are one of the main cause of VC equipment not communicating. Firewall configuration is a major consideration when deciding on VC equipment technologies.
firewall traversal
Firewall traversal technology creates a secure path through the firewall barrier safely and seamlessly
G
gatekeeper
In the H.323 world, the gatekeeper provides several important functions. First, it controls access to the network, allowing or denying calls and controlling the bandwidth of a call. Second, it helps with address resolution, making possible email type names for end users, and converting those into the appropriate network addresses. They also handle call tracking and billing, call signalling, and the management of gateways.
gateway
A network device that allows an H.323 (Internet-based) videoconference device to connect to an H.320 (ISDN) videoconference device. It is essentially an adapter to allow dissimilar network devices to exchange information.
H
I
IP
The Internet Protocol. IP is the basic language of the Internet. It was developed by the government for use in internetworking multiple computer networks together.
ISDN
Integrated Services Digital Network. This set of standards allows multiple digital channels at 64Kbps to be used on top of the standard Public Switched Telephone Network (PSTN) infrastructure. BRI and PRI are common configurations of ISDN connections.
J
jitter
The change in latency with time. This is a network problem that is very important to video quality. Significant jitter destroys video.
K
L
latency
The length of time it takes a packet to move from source to destination; delay.
loopback test
A testing often found in the menus of videoconference systems. It creates a virtual connection with itself, and allows the user to see the video and hear the audio signals they are transmitting.
lossless compression
Refers to data compression techniques in which no data is lost. For most types of data, lossless compression techniques can reduce the space needed by only about half. Only certain types of data can tolerate lossy compression. Lossless compression technique when compressing data and programs.
lossy compression
Refers to data compression techniques in which some amount of data is lost. Lossy compression technologies attempt to eliminate redundant or unnecessary information. Most video compression technologies, such as MPEG, use a lossy technique.
M
MPEG
MPEG (Moving Picture Experts Group) is a series of ISO standards for digital video and audio, designed for different uses and data rates.
N
O
P
packet
A unit of information sent across a (packet-switched) network. A packet generally contains the destination address as well as the data to be sent.
port
Logical endpoints used by TCP and UDP networking protocols to distinguish specific data channels on a network interface.
Q
QuickTime
A file-format and architecture developed by Apple for use with digital audio and video. Available on most computing platforms.
R
real time
A transmission that occurs right away, without any perceptible delay. Very important in video conferencing, as much delay will make the system very unusable.
S
streaming media
Sending video or audio over a network as needed, instead of forcing the user to download the entire file before viewing it. Typically a few seconds of data is sent ahead and buffered in case of network transmission delays. (Although some data is buffered to the hard drive, it is written to temporary storage and is gone once viewing is complete).
T
T.120
T.120 is an ITU-T standard (International Telecommunications Union) for document conferencing. Document conferencing allows two or more people to concurrently view and edit a document across a network. T.120 is the commonly used name to refer to a family of distinct standards.
TCP/IP
Transmission Control Protocol over Internet Protocol. It is the combined Ethernet protocol standard that covers both network and transport layers.
teleconferencing
Two or more people who are geographically distant having a meeting of some sort across a telecommunications link. Includes audio, video, and/or data conferencing.
U
V
VC
Acronym for Video conferencing
voice activated switching
Automatically switching the video feed to whoever is speaking in a multipoint videoconference. Usually a function of the MCU (multipoint conferencing unit)