Proximity
Videoconferencing Glossary
algorithm
A step-by-step problem-solving procedure. Transmission
of compressed video over a communications network requires
sophisticated compression algorithms. Some videoconferencing
systems offer both proprietary and standard compression
algorithms.
analog signals
Audio/video signals currently used in broadcasting where
the signal is represented by variable measurable physical
quantities (such as voltage). Current TV and radio
signals are analog, as are many telephone lines. (Contrast
with digital). Example devices: video camera, VCR,
projector, scan converter, document camera, sound system.
audio
In video communications, electrical signals that carry
sounds. The term is also used to describe systems concerned
with sound with recording and transmission; speech
pickup systems, transmission links that carry sounds,
amplifiers and the like. Example devices: microphones,
audio mixer.
audio bridge
Equipment that mixes multiple audio inputs and feeds
back composite audio to each station after removing
the individual station's input.
bandwidth
In casual use, the amount of information that can be
transmitted in an information channel. High bandwidth
Internet access means those web graphics load quickly
on Netscape. High bandwidth videoconferencing means
that the picture and sound will be clear. In computers,
the speed at which data can be transmitted on a communications
frequency. In telecommunications, the maximum frequency
(spectrum) measured in Hertz or cycles per second,
between the two limiting frequencies of a channel.
B channel
The ISDN circuit-switched bearer channels, capable of
transmitting 64 Kbps of digitized information.
bps
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)
bridge
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.
carrier
A term used to refer to various telephone companies that
provide local, long distance or value added services;
alternately, a system or systems whereby many channels
of electrical information can be carried over a single
transmission path. Example carriers: AT&T, MCI,
Sprint.
codec
Coder-Decoder. Videoconferencing hardware that codes
the outgoing video and audio signals and decodes the
incoming signals. Prior to transmission, the codec
converts analog signals to digital signals and compresses
the digital signals. Incoming audio and video must
be decompressed and converted from digital back to
analog.
compressed video
When the vast amount of information in a normal TV transmission
(90 Mbps) 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 (ISDN). Some information is sacrificed in the
process, which may result in diminished picture and
sound quality.
desktop videoconferencing
Videoconferencing on a personal computer is most appropriate
for small groups or individuals (compare with room-based
videoconferencing). Many desktop videoconferencing
systems support document sharing.
digital signals
Audio/video signals represented by discrete variations
(in voltage, frequency, amplitude, location, etc.).
A digital clock, for example, displays the time as
discrete numeric values rather than angular displacement
of analog hands. In general, digital signals can be
transmitted faster and more accurately than analog
signals. As an example, music from digital cd's is
usually more clear than music from analog records.
(Contrast with analog signals.)
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.
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.
full-motion video
Video reproduction at 30 frames per second (fps) for
NTSC signals or 25 fps for PAL signals. Also known
as continuous-motion video. In the videoconferencing
world, the term "full-motion video" is often
used, and often misunderstood. Videoconferencing systems
cannot provide 30 fps for all resolutions at all times
nor is that rate always needed for a high-quality,
satisfying video image. Picture quality must sometimes
be sacrificed to achieve interactive visual communication
across the telephone network economically. Videoconferencing
vendors often use "full-motion video" to
refer to any system that isn't still-frame. Most videoconferencing
systems today run 10 to 15 frames per second at 112
Kbps. Need 384 Kbps in order to transmit 30 FPS.
H.320 standard
A widely-used video compression standard that allows
a wide variety of videoconferencing systems to communicate
utilizing ISDN telephone lines.
H.323 standard
A widely-used video compression standard that allows
a wide variety of videoconferencing systems to communicate
utilizing IP (Internet Protocol).
ISDN - Integrated Services Digital Network
A CCITT standard for integrated transmission of voice,
video and data. Bandwidths include: Basic Rate Interface
- BR (144 Kbps - 2 B & 1 D channel) and Primary
Rate - PRI (1.544 and 2.048 Mbps).
Integrated Services Digital Network. A set of protocol
and interface standards that effectively constitute an
integrated (voice, video, and data) telephone "network." These
standards promote global availability and compatibility
of ISDN products and services. The two types of ISDN
discussed in this Guide are Basic Rate Interface (BRI)
and Primate Rate Interface (PRI). ISDN BRI (ISDN Basic
Rate Interface) is the interface to connect the desktop
to the digital long distance network. ISDN BRI provides
two 64Kbps B ("bearer") channels to carry information
content, the voice, video, and data substance of a transmission.
A separate 16Kbps D ("data") channel is used
for call setup and signaling. ISDN BRI is often called "2B+D" ISDN,
for its combination of two B and one D channel. This
service is marketed and supported by the LECs. ISDN PRI
(Primary Rate Interface) is the ISDN equivalent of a
T-1 circuit. It provides 23B+D (in North America) or
30B+D (in Europe) running at 1.544 Mbps and 2.048Mps,
respectively. Each channel (time slot) is 64Kbps. One
channel is reserved as the D channel; the other 23, as
bearer channels (23+D).
Kbps
Kilobits per second. Refers to transmission speed of
1,000 bits per second.
multi-point videoconference
Videoconference with more than two sites. The sites must
connect via a video bridge. (Compare with point-to-point
videoconference.)
NT 1
Network Termination type 1. The NT-1 is a device which
converts the two-wire line (or "U" interface)
coming from your telephone company into a 4-wire line
(or "S/T" interface). The NT- 1 is physically
connected between the ISDN board of your videoconferencing
system and your ISDN phone line. The NT- 1 supports
network maintenance functions such as loop testing.
Check to see if your ISDN equipment requires an external
NT-1 to operate.
NTSC - National Television Standards Committee (Never
Twice the Same Color)
A video standard established by the United States (RCA/NBC}
and adopted by numerous other countries. This is a 525-line
video with 3.58-MHz chroma subcarrier and 60 cycles per
second. Frames are displayed at 30 frames per second.
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 multi-point
videoconference.)
POTS
Plain Old Telephone Service. Conventional analog telephone
lines using twisted-pair copper wire. This is used
to provide residential service.
public room
Videoconferencing service offered to the public on a
fee-for-usage basis.
room-based videoconferencing
Videoconferencing using a sophisticated system is appropriate
for large groups. (Compare to desktop videoconferencing.)
room coordinator
A room coordinator (room monitor) is there to make sure
the equipment is on and operational, greet the incoming
attendees and be nearby in case something is needed
i.e. adjust the volume, troubleshoot, indicate where
the closest rest room is! They are not necessarily
present in the room during the actual videoconference.
Switched 56
Switched 56 service allows customers to dial up and transmit
digital information up to 56,000 bits per second in
much the same way that they dial up an analog telephone
call. The service is billed like a voice line-a monthly
charge plus a cost for each minute of usage. Nearly
all LECs and IXCs offer switched 56 service and any
switched 56 offering can connect with any other offering,
regardless of which carrier offers the service.
T-1
The transmission bit rate of 1.544 millions bits per
second. This is also equivalent to the ISDN Primary
Rate Interface for the U.S. The European T1 or E1 transmission
rate is 2.048 million bits per second.
TELCO
Generic term for the local telephone company. Can refer
to an Interexchange Carrier or to the Local Exchange
Carrier.
whiteboarding
A term used to describe the placement of shared documents
on an on-screen "shared notebook" or "whiteboard." Desktop
videoconferencing software includes "snapshot" tools
that enable you to capture entire windows or portions
of windows and place them on the whiteboard. You can
also use familiar Windows operations (cut and paste)
to put snapshots on the whiteboard. You work with familiar
tools to mark up the electronic whiteboard much like
you do with a traditional wall mounted board.
videoconferencing
Communication across long distances with video and audio
contact that may also include graphics and data exchange.
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