V.35 - ITU-T standard describing a synchronous, physical layer protocol
used for communications between a network access device and a packet network.
V.35 is most commonly used in the United States and Europe, and is recommended
for speeds up to 48 Kbps.
VA (Volt Ampere) - The product of voltage and current in a circuit. In a
DC circuit, it is equivalent to the power (watts); in an AC circuit, it is
equal to power (watts) divided by the power factor.
Value Added - A voice or data network service that uses available
transmission facilities and adds some other service or services to increase the
value of the transmission.
Vaporware - A slang term for software which has been announced and
perhaps even demonstrated, but has not been delivered to commercial customers.
Variable Impedances - Capacitors, inductors, or resistors which are
adjustable in value.
Varistor - A variable resistor. A device which does not have a linear
VBR (Variable Bit Rate)
- a type of traffic that, when sent over a network, is tolerant of delays and
changes in the amount of bandwidth it is allocated (e.g., data applications).
VC (Virtual Channel (or Circuit))
- a communications path between two nodes identified by label rather than fixed
VCC (Virtual Channel Connection)
- a unidirectional concatenation of VCLs that extends between the points where
the ATM service users access the ATM Layer. The points at which the ATM cell
payload is passed to, or received from, the users of the ATM Layer (i.e., a
higher layer or ATMM-entity) for processing signify the endpoints of a VCC.
VCI (Virtual Channel Identifier)
- the address or label of a VC; a value stored in a field in the ATM cell
header that identifies an individual virtual channel to which the cell belongs.
VCI values may be different for each data link hop of an ATM virtual
VCL (Virtual Channel Link)
- a means of unidirectional transport of ATM cells between the point where a
VCI value is assigned and the point where that value is translated or removed.
VDT (Video Display Terminal) - A data terminal with a TV screen.
VF (Voice Frequency) - An audio frequency in the range essential for
transmission of speech, typically from about 300 Hz to 3000 Hz.
VFD (Vacuum Fluorescent Display) - A light-emitting triode utilizing
fluorescent phosphors which can be used in alphanumeric display panels.
VGA (Variable Graphics Array) - A graphics standard developed by IBM for
the IBM PC which allows the PC’s screen to generate any of four levels of
VINES (Virtual Network Software)
- Banyan's network operating system based on UNIX and its protocols.
Virtual Channel Switch
- a network element that connects VCLs. It terminates VPCs and translates VCI
values. The Virtual Channel Switch is directed by Control Plane functions and
relays the cells of a VC.
- an endpoint-to-endpoint connection in an ATM network. A virtual connection
can be either a virtual path or a virtual channel.
Virtual Path Switch
- a network element that connects VPLs, it translates VPI (not VCI) values and
is directed by Control Plane functions. The Virtual Path Switch relays the
cells of a Virtual Path.
VLAN (Virtual Local Area Network)
- Work stations connected to an intelligent device which provides the
capabilities to define LAN membership.
VLV (Very Low Voltage) - A discrete lead designation used to reflect a
low voltage condition at plant batteries at the maximum limit setting on the
plant connected from a grounded or looped break lead (classified the same as
the LV2 alarm).
Voice-Activated Dialing - A feature that permits you to dial a number by
calling the digits out to your cellular phone instead of punching them in
yourself. The technology has advanced to the point that several models of
mobile phones are now offered with the feature, which contributes to
convenience as well as driving safety.
Voice Mail (or Voice Messaging) - A computerized, highly sophisticated
answering service that automatically answers your call, plays a greeting in
your own voice and records a message. Depending on the sophistication of the
service, it also can notify you via a pager that you have received a call.
After you have retrieved your messages, you can delete them, save them, reply
to them or forward them to someone else on your voice mail system.
Volatile - Descriptive of a data storage device that loses its contents
when power is lost (turned off).
Volt - The derived SI unit of electric potential difference.
Voltage - Potential difference between two points. The measurement of
electrical potential in a conductor.
Voltage Alarm Relay - Relay constructed on a voltmeter, with alarm
contacts which close whenever the voltage falls below a specified minimum or
rises above a specified maximum.
Voltage Dip - The instantaneous reduction in voltage resulting from an
increase in load.
Voltage Droop - The difference in voltage between no load and full load,
expressed in percent of the full load value.
Voltage Drop - A reduction in voltage level caused by a current flowing
through an impedance; equal to the current impedance product.
Voltage Drop (DC Feeder) - A reduction in voltage in conductors caused by
current flowing through its resistance. It is equal to the product of current
times feeder resistance.
Voltage Drop Calculation - For a given length of a DC feeder, one way
distance: Voltage Drop = k x amps x feet / circular mils where k = 11.1 for
copper and k = 17.4 for aluminum.
Voltage Gradient - Potential drop per unit length of a conductor, or per
unit thickness of a dielectric.
Voltage Noise - Unwanted electrical signals which produce undesirable
noise in the circuits of the control systems in which they occur.
Voltage Regulation (Battery Chargers) - A measure of how well a rectifier
battery plant can control the steady state DC output voltage under two extreme
conditions: (1) Vo at no load current with the input AC voltage at the designed
maximum value, called Vomax; (2) Vo at full load current with the input AC
voltage at the designed minimum value, called Vomin. %Regulation = ((Vomax -
Vomin) /(Vomax + Vomin)) x 100 Note: "±" is used to distinguish the above
regulation formula from the classical equipment formula defined as: %Regulation
= ((Vonl -Vofl) / Vofl) x 100 where fl = full load, nl = no load and Vin is
kept at rated value.
Voltage Regulation/Stabilization - The maintaining of a voltage source
within required limits despite fluctuations in input voltage or load.
Voltage Regulator - A device which maintains its output voltage at a
constant level. Such devices often depend on saturated core operation for
Voltage Spike - A short duration transient that exceeds the average
amplitude of the associated signal.
Voltmeter - An instrument for measuring voltages.
VP (Virtual Path)
- a unidirectional logical association or bundle of VCs.
VPC (Virtual Path Connection)
- a concatenation of VPLs between virtual path terminators (VPTs). VPCs are
VPDN (Virtual Private Data Network)
- a private data communications network built on public switching and transport
facilities rather than dedicated leased facilities such as T1s.
VPI (Virtual Path Identifier)
- the address or label of a particular VP; a value stored in a field in the ATM
cell header that identifies an individual virtual path to which the cell
belongs. A virtual path may comprise multiple virtual channels.
VPL (Virtual Path Link)
- a means of unidirectional transport of ATM cells between the point where a
VPI value is assigned and the point where that value is translated or removed.
VPN (Virtual Private Network)
- a private voice communications network built on public switching and
transport facilities rather than dedicated leased facilities such as T1.
VPT (Virtual Path Terminator)
- a system that unbundles the VCs of a VP for independent processing of each
VS/VD (Virtual Source/Virtual Destination)
- An ABR connection may be divided into two or more separately controlled ABR
segments. Each ABR control segment, except the first, is sourced by a virtual
source. A virtual source implements the behavior of an ABR source endpoint.
Backwards RM-cells received by a virtual source are removed from the
connection. Each ABR control segment, except the last, is terminated by a
virtual destination. A virtual destination assumes the behavior of an ABR
Forward RM-cells received by a virtual destination are turned around and not
forwarded to the next segment of the connection.
VT (Virtual Tributary) - a structure used to carry payloads such as DS1s
that run at significantly lower rates than STS-1s.