Algorithm - A set of specifications that define methods
and procedures for transmitting audio, video, and data.
Analog Gateway - A means of connecting dissimilar
codecs. Incoming digital signal from one type of codec is decoded
by a similar codec and converted to analog. The Analog signal is
then passed to the dissimilar codec, coded, and decoded at the far
end. Analog gateways achieved interoperability in a nonstandard
environment, but have the disadvantages of degrading video and
audio quality and often reducing functionality.
Annex D Graphics - An addendum to the H.320
videoconferencing protocol used for still image transfer between
dissimilar videoconferencing systems.
ATM - Asynchronous Transfer Mode. An emerging networking
method that can be used for carrying voice, video and data
simultaneously over low speed (T1 - 1.5 Mbps) or very high speed
(622 Mbps) networks.
Bandwidth - Amount of transmission capacity.
Basic Rate Interface (BRI) - An ISDN access or
subscriber line, consisting of two 64Kbps B ("bearer")
channels and one 16Kbps D channel used for both data and signaling
Broadcast - One-way video, usually from a single
transmitting site to many receiving sites. In some cases, the
receiving sites can communicate to the transmitting site on an
CCITT - International Telephone and Telegraph Consultative
Committee. Now known as ITU-T. An international body that sets
worldwide telecommunications standards, such as the Px64 standard
Channel Bank - Used to divide a T1 access facility into
24 digital or analog circuits.
Channel Service Unit (CSU) - A type of customer premise
equipment that terminates a T1 access facility to a channel bank,
PBX or other equipment capable of supporting a T1 interface.
Codec - Coder-Decoder: a device that encodes an incoming
analog signal into a digital signal for transmission to another
codec. The digital signal is decoded into analog format. In
videoconferencing, codecs typically code and decode video and audio.
Compression - Reduction of the amount of information to
accommodate cost-effective digital transmission to another codec.
For example, sub-T1 video codecs compress analog signals (roughly
equivalent to 90,000 kilobits per second) to digital rates varying
from 56 to 1,544 kilobits per second.
Compression Ratio - A compression ratio, usually
expressed as 5:1, refers to the size of the original data versus
the size after compression. If data has been reduced to one-fifth
the original size, the compression ratio is 5:1.
Dedicated Line - A permanently assigned path connecting
geographically dispersed sites on a long distance network.
Synonym: private line: leased line.
Delay - Refers to the slight delay that sometimes occurs
when transferring video, data and audio signals.
DES - Digital Encryption Standard, an encryption method
defined by the National Bureau of Standards.
Digital - Information contained in the form of 0s and 1s
for transmission on digital media, including fiber, microwave, and
satellite. Digital information may include video, audio, graphics,
Digital Service Unit (DSU) - A type of customer premise
equipment that terminates a single DSO or fractional T1.
DS0 - Digital Signal level zero. One 56Kbps (or 64Kbps)
line or circuit.
DS1 - Digital Signal level one. One 1.544Mbps digital
signal comprised of 24 lines or channels, each with 64 Kbps
capacity (see T1).
Digital Switch - A means of supporting multiway
conferencing using the signals in their digital format without
converting them to analog. Digital switches permit multiple users
with similar codecs to conference generally with voice-activated
Dual 56 - Combination of two 56Kbps lines for a 112Kbps
video transmission capacity. Dual 56 typically allows direct
dialing of a videoconference call.
E1 - High speed 2.048Mbps digital line with 32 channels,
each operating at 64 Kbps. E1 is only available outside the U.S.
Encryption - Alteration of transmitted information to
protect it from unauthorized tapping.
FCIF or (CIF) - Full Common Intermediate Format. A video
resolution of 352 pixels horizontally and 288 pixels vertically.
It is used primarily in higher bit rate (128Kbps and higher) video
Flash Memory - Memory which occupies little space and
does not need continuous power to be retained.
F.R.A.D. - Frame Relay Access Device: F.R.A.D. takes the
information streams and multiplexes them on public or private
frame relay networks.
Frame Relay - A packet switched networking technology
used for low speed (T1 - 1.5Mbps and lower) WAN connections.
Primarily used to connect a company's routers on their data
Frames Per Second (fps) - Frequency with which video
frames appear on a monitor. Broadcast-quality video generally
consists of 30 frames per second. Full-motion videoconferencing
typically offers video in the range of 10 - 15 frames per second.
At very low bandwidths, such as 56 or 112 Kbps, the frame rate may
Full-Duplex Audio -Audio that allows local and remote
conference participants to speak simultaneously without losing
audio contact. Full-duplex audio may be provided in a
point-to-point or multipoint conference.
Full-Motion - In compressed video, picture quality that
is generally acceptable to users although not of broadcast
quality. Typically full-motion compressed video provides anywhere
from 10 - 30 frames per second depending on the bandwidth
Graphics - Transmission of still images, usually from a
video source, but in some cases PC-generated.
G.711 - 3KHz audio-coding at 64Kbps.
G.722 - 7KHz audio-coding at 64Kbps.
G.728 - 3KHz audio compression at 16Kbps (wideband
Half-Duplex Audio - Audio that permits only one site to
speak at a time.
H.320 -Umbrella standard for videoconferencing.
H.221 - The ITU-T standard relating to communications
protocol for videoconferencing.
H.231 - Multipoint for linking three or more H.320
H.261 - The ITU-T Px64 standard relating to the video
H.230 - The ITU-T standard that defines call control and
H.242 - Call set-up and disconnect of two point
H.233 - Encryption.
H.243 - Defines call control procedures between H.231
MCU and H.320 codecs.
H.323 - Video over LAN/WAN.
H.324 - Video over POTS.
In-band - Transmission taking place within allocated
bandwidth. For example, a video call with total of 384Kbps may
allocate 64 Kbps for audio, leaving 320Kbps for video.
Integrated Presentation System - Presentations such as
those created in Microsoft® PowerPoint®, can be displayed and
presented to the far site while simultaneously being presented to
remote users connected via the Internet/Intranet.
Interactive - Communication in which all participating
sites have equal capability. Interactive videoconferencing permits
all sites to see and hear one another.
Interoperability - Communication between dissimilar
codecs. The ITU-T Px64 standard is designed to permit
Inverse Multiplexer (Imux) - A device that creates a
single higher-speed transmission by combining and synchronizing
two or more channels.
ISDN (Integrated Services Digital Network) - A switched
network service providing end-to-end digital connectivity for
transmitting voice, data, and video simultaneously over a single
line verses multiple lines. Uses high-speed, out-of-band signaling.
There are two major forms of ISDN: BRI and PRI.
ITU-T - International Telecommunications Union-Telephony
Sector. Formerly known as CCITT. An international body that sets
worldwide telecommunications standards, such as the Px64 standards
JPEG - Joint Pictures Experts Group. Still-frame
graphics for multimedia.
Kilobits per Second (Kbps) - Measure of rate of digital
transmission, often abbreviated Kbps.
LEC - Local Exchange Carrier; provides local
telecommunications service and access to long distance networks.
Local Loop - The communications lines between the long
distance subscriber and the LEC switching center.
Loopback - A diagnostic test where a signal is
transmitted over a communications link or network and then
returned to the sending device. Loopbacks are used to make sure
the video equipment is working properly and as a way to
Multiplexer - A device that permits subdivision of a
given bandwidth. For example, a T1 Multiplexer may divide a T1
line (1,544Kbps) into two capacities of 768Kbps each.
MPEG - Motion Pictures Experts Group: This is a standard
for motion video.
Multiway - Communication between more than two sites.
Multiway communication may occur through a digital switch or
through an analog gateway.
Multipoint Control Unit - Device which allows more than
two sites to be connected in a videoconference. Sometimes called a
digital switch or video bridge.
NTSC - North American standard for analog video format.
National Television Systems Committee.
Out of band - Transmission taking place external to
allocated bandwidth. A video call with out-of-band audio requires
a separate phone line for the audio.
PAL - European standard for analog video format.
Pixel - Picture element; a measure of resolution for
Primary Rate Interface (PRI) - An ISDN subscriber line
consisting of 23 64Kbps B channels and one 64Kbps D channel used
POP - Point-of-Presence. The location or office where a
line from an Inter-Exchange Carrier (IXC) connects to the local
telephone company or directly to the user.
POTS - Plain Old Telephone System. The analog phone
system (including telephones, modems, central offices switches,
etc.) currently in use around the world.
Px64 - The ITU-T's international video standard which
provides a standard algorithm for video compression and
decompression. Formally known as H.261, it was adopted in December
QCIF - Quarter Common Intermediate Format. A video
resolution of ¼ the size of FCIF - 176 pixels horizontally and
144 pixels vertically. It is used primarily in low bite rate
(128Kbps and lower) videoconferencing.
RBOC - Regional Bell Operating Company; controls a
grouping of local exchange carriers.
Resolution - A measure of sharpness or clarity on a
RSVP - Resource Reservation Protocol. An emerging data
network standard protocol used to reserve bandwidth within packet
networks. It is primarily used in data network routers to
guarantee a fixed bandwidth through the router for a single or
group of users using real time data (like voice or video). All
other traffic not assigned to the reservation (such as e-mail or
Web access) is delivered by best effort by the router (as it is
RS-232 - Connectivity from the codec permitting data
inputs for transmission from .3 to 190.2 Kbps.
RS-449 - Transmission interface between the codec and
the transmission link that typically connects to a T1 Multiplexer.
A user RS-449 port may also be available for data transfer.
SECAM - French standard for analog video format.
SNMP - Simple Network Management Protocol; the protocol
governing network management and monitoring of network devices and
their functions. SNMP came out of the TCP/IP environment.
Standards - Uniform specifications to permit
interoperability in videoconferencing.
Switched 56 - Transmission network at 56Kbps that allows
dial-up videoconferencing. Because picture quality at 56Kbps is
often not acceptable, most dial-up videoconferencing takes place
on two 56Kbps lines, for a total of 112Kbps (see Dual 56).
TCP/IP - The international standard protocol used on the
Internet and company data networks. It provides worldwide
connectivity and includes services such as the World Wide Web,
e-mail, file transfer and remote terminal login.
Transmission Speed - Data rate for videoconferencing,
usually expressed in Kbps.
T1 - Commonly used transmission line for
videoconferencing, with a capacity of 1,544Kbps.
T.120 - Multilayer protocols for graphics/data
T3 - A 45Mbps leased line. Usually obtained from a local
or long distance telephone carrier.
Videoconferencing - Communication across long distances
with video and audio contact.
Voice Activated Switching - In multiway
videoconferencing, used so that all participating sites
automatically see the site which is currently speaking.
Voice-tracking - camera automatically tracks the voice
of the person speaking.
V.35 - Transmission interface between the codec and the
transmission link that permits Switched 56 connectivity.
Web Server - A computer that delivers (serves up) Web
pages. Every Web server has an IP address and possibly a domain
name. For example, if you enter the URL
http://www.sandybay.com/index.html in your browser, this sends a
request to the server whose domain name is sandybay.com. The
server then fetches the page named index.html and sends it to your
Web Browser - A software application used to locate and
display Web pages. Three of the most popular browsers are Netscape
Navigator, Microsoft Internet Explorer, and Spyglass Mosaic. All
of these are graphical browsers, which means that they can display
graphics as well as text. In addition, most modern browsers can
present multimedia information, including sound and video.