VBR (Variable Bit Rate). An ATM
Forum defined service category which supports variable bit
rate data traffic with average and peak traffic parameters.
VC (Virtual Channel). A communications
channel that provides for the sequential uni-directional transport
of ATM cells.
VCC (Virtual Channel Connection).
A 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 (that is, a higher layer or ATM-entity) for processing
signify the endpoints of a VCC. The VCCs are uni-directional.
VCI (Virtual Channel Identifier).
A unique numerical tag as defined by a 16-bit field in the
ATM cell header that identifies a virtual channel, over which
the cell is to travel.
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.
VHF (Very High Frequency). Refers
to electomagnetic signals between approximately 54 MHz and
300 MHz.
VLR (Visitor Location Register).
A database that is updated by the MSC
with selected subscriber information from the HLR
when the subscriber 'roams' into the location (MSC service
area) controlled by the VLR.
VP (Virtual Path). A unidirectional
logical association or bundle of VCs.
VPC (Virtual Path Connection). A
concatenation of VPLs between Virtual Path Terminators (VPTs).
The VPCs are uni-directional.
Voice grade channel/line.
A channel offering the minimum bandwidth for the transmission
of voice signals. Normally 300 bps to 3.4 kpbs.
Voice mail. A system that
records, stores and retrieves voice messages. In cellular
telephone systems a number of features come with voice mail
such as call
forwarding. The short messaging service (SMS)
is a unique feature of voice mail for digital cellular phones.
V-Series. A set of recommendations
(or protocols)
from the ITU-TS governing data transmission over telephone
lines. Included in the V-series of protocols are:
- V.21 300 bps duplex modem for use over PSTN.
- V.22 1200 bps duplex
modem for use over PSTN and leased lines.
- V.22 bis 2.4 kbps duplex modem for use over PSTN and leased
lines.
- V.23 600/1200 bps modem
for use over PSTN.
- V.24 Definitions of interchange circuits between DTE
and DCE.
- V.25 bis Automatic calling and answering equipment on
the PSTN.
- V.26 2.4 kbps modem for use over leased lines.
- V.26 bis 2400/1200 bps half-duplex
modem for use over PSTN.
- V.26 ter 2400/1200 bps
full duplex modem for use over PSTN.
- V.27 4.8K kbps modem for use over leased lines.
- V.27 bis 4800/2400 bps modem for use over leased line.
- V.27 ter 4800/2400 bps modem for use over PSTN.
- V.29 9.6 kbss modem for use over leased lines.
- V.32 Up to 9.6 kpbs bps modem for use over PSTN or leased
lines.
- V.32 bis Up to 14.4 kbps modem for use over PSTN or leased
lines.
- V.42 Error control procedures.
- V.42 bis Data
compression technique for use with V.42
VSWR
(Voltage Standing Wave Ratio) The ratio of the maximum
value of a standing
wave to its minimum value. The result indicates the level
of disparity in an antenna system.