Van (Value Added Network)/Vans (Value Added
Network Service) A data transmission network
which guarantees data security and integrity through added computer
control and communications, from the sender to the recipient often
in the manner of a door-to-door courier or freight forwarder.
Vaporware Products
announced but not yet commercially available. Often used by suppliers
to lock users in with the promise of great things to come.
Videoconferencing Video
and audio communication between two or more parties via a video-codec
(coder/decoder) at either end linked by digital circuits. Formerly
needing in excess of 300Mbit/s bandwidth, systems are now available
offering acceptable quality for general use at 128Kbit/s and high-quality
71KHz audio. Factors influencing the growth of videoconferencing
are improved compression technology, reduced cost through VLSI
chip technology, low-cost switched digital networks - particularly
ISDN - the emergence of standards and applications. Main players
include BT, PictureTel and Compression Labs Inc.
Videoconferencing standards ITU-TS
H.261 was the standards watershed. Announced in November 1990,
it relates to the decoding process used when decompressing videoconferencing
pictures, providing a uniform process for codecs to read the incoming
signals. Originally defined by Compression Labs Inc. Other important
standards are H.221: communications framing; H.230 control and
indication signals and H.242d: call set-up and disconnect. Encryption,
still-frame graphics coding and data transmission standards have
still to be developed.
Videotex Term invented
by the ITU to describe TV equipment used to display computer-based
data, whether sent via a telephone (often called viewdata) or
a broadcasting charnel (Teletext). ITU distinguishes between interactive
or broadcast videotex.
VIM (Vendor Independent Messaging) Standard
for the application interface to e-mail from Lotus, WordPerfect
and others. It will include MAPI compliance.
Vines Banyan Systems'
Virtual Networking operating system is based on Unix system V.
This network operating system provides transparent communication
across heterogeneous networks and is more expansive in concept,
although attracting far fewer users, than Novell's NetWare.
Virtual circuit A
link that seems and behaves like a dedicated point to point line
or a system that delivers packets in sequence, as happens on an
actual point to point network. In reality, the data is delivered
across a network via the most appropriate route. The sending and
receiving devices do not have to be aware of the options and the
route is chosen only when a message is sent. There is no prearrangement,
so each virtual connection exists only for the duration of that
one transmission.
Virtual Container (VC) SDH
defines a number of Containers, each corresponding to an existing
plesiochronous rate. Information from a plesiochronous signal
is mapped into the relevant container along with control information
known as the "path overhead". The container plus path
overhead form a VC.
Virtual LAN A logical
rather than a physical LAN comprising workgroups drawn together
for business reasons or for a particular project irrespective
of each member's actual location. Members are likely to belong
to several such LANs as their job function dictates. Such LANs
await the maturity of high-speed transmission technologies such
as ATM before they can exist in any viable form.
Virtual teams Ad hoc
groups of users formed to solve particular problems without taking
them away from their desks. A useful option made feasible with
groupware.
Virtual company Company
built on the basis of teleworking with limited central office
administration. Made possible by improved communications and groupware
software, it is a phenomenon of the future.
VPN (Virtual Private Network) The
provision of private voice and data networking from the public
switched network through advanced public switches. The network
connection appears to the user as an end-to-end, nailed-up circuit
without actually involving a permanent physical connection, as
in the case of a leased line. VPNs retain the advantages of private
networks but add benefits like capacity on demand.
Virus Code that attaches
itself to a program and makes copies of itself. It may or may
not cause accidental or malicious damage, but is a serious nuisance
particularly in a networked environment and where dependence on
IT is heavy. Anti-virus applications such as Norton are available,
but security should be augmented by procedures and regular backups.
Voice-grade channel, Voice-grade line A
channel or line offering the minimum bandwidth suitable for voice
frequencies, usually 300bit/s to 3.4Kbit/s.
Voice Mail A system
that records, stores and retrieves voice messages; either a standalone
device or those that integrate to some extent with a user's phone
system. Standalone voice mail is similar to a collection of answering
machines but able to instruct each machine (voice mailbox) to
carry out a range of features such as call forwarding. Messages
can be delivered at a pre-arranged time, tagged and edited. Integrated
systems indicate messages waiting via a light on a user's phone
and/or an alphanumeric display. If the phone rings for a specified
number of rings, it can default to a mailbox which delivers its
invitation to leave a message and records the results.
VSAT (Very Small Aperture Terminal) One-meter
diameter satellite dishes used by remote sites, as opposed to
the 3m dishes used by head office, in a satellite-linked network.
The central office is able to broadcast or multicast data to the
remote sites. In Europe, regulatory restrictions are gradually
being lifted to allow two-way transmission. The US does not labor
under the same protectionism and so has a flourishing VSAT community
that allows the remote site to reply using the same link.
V.Fast Forerunner
to the V.34 modem standard due for ratification by 1995. V.Fast
modems send a 1Mbyte file typically in under 1.5 minutes.
V Series A group of
ITU-TS recommendations governing data transmission over telephone
lines. Series includes:
V.21 300bit/s duplex
modem for use over PSTN
V.22 1200bit/s duplex
modem for use over PSTN and leased lines
V.22 bis 2.4Kbit/s
duplex modem for use over PSTN and leased lines.
V.23 600/1200bit/s
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 2.4Kbit/s modem
for use over leased lines
V.26 bis 2400/1200bit/s
half duplex modem for use over PSTN.
V.26 ter 2400/1200
bit/s full duplex modern for use over PSTN.
V.27 4.8Kbit/s modem
for use over leased lines.
V.27 bis 4800/2400bit/s
modem for use over leasedline.
V.27 ter 4800/2400bit/s
modem for use over PSTN
V.29 9.6Kbit/s modem
for use over leased lines.
V.32 Up to 9.6Kbit/s
bps modern for use over PSTN or leased lines.
V.32 bis Up to 14.4Kbit/s
modem for use over PSTN or leased lines.
V.42 Error control
procedures.
V.42 bis Data compression
technique for use with V.42
VTAM (Virtual Telecommunications Access Method)
An IBM software routine: the virtual access
method for 3270 systems.
