Glossary - V

V.22 (protocol, communications)

An IUT-T modem protocol which allowed data rates of 1200 bits per second. V.22bis doubled this.

V.22bis (protocol, communications)

An IUT-T modem protocol which allowed data rates of 2400 bits per second, twice that of V.22.

V.32 (protocol, communications)

The IUT-T standard protocol for modems transmitting at 4800 or 9600 bits per second. V.32bis extended this to 14400 bps. V32 and V.32bis acheive bidirectional data transmission not by having different sets of tones at each end but by subtracting what is sent from what is received.

V.32bis (protocol, communications)

V.32 twice. An extension of the IUT-T V.32 modem protocol allowing speeds of 7200, 12000 and 14400 bits per second. The modem should select the appropriate speed according to the current line conditions. See also V.32ter.

V.32ter - V.32terbo (protocol, communications)

An extension of the IUT-T V.32bis modem protocol. While waiting for V.34, many modem manufacturers decided to extend V.32bis to 19.2 kbps. This was known as V.32ter which some marketroids rechristened V.32 terbo which is not only misspelled but misses the fact that V.32ter means the third revision of V.32.

V.34 (protocol, communications)

A modem operating at data signalling rates of up to 28 800 bits per second (2400, 2743, 2800, 3000, 3200 and 3429 and up to 28800 bits per second) for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits.
During the lengthy process of approval by IUT-T, many manufacturers released 28.8 kbps modems described as V.FAST. The V.34 recommendation was ratified by ITU-T on 20 September 1994. Rockwell and US Robotics both have seats on the ITU-T, and have both released chip set/BIOS combinations that they feel will meet V.34. V.34 modems will also support V.FC if the manufacturer currently supports V.FC (e.g. Rockwell).
Ref: IUT-T V 34.

V.34bis (protocol, communications)

A draft IUT-T standard for modem transmitting at 33600 bps.

V.35 (protocol, communications, standard)

The IUT-T standard for data transmission at 48 kilobits per second over 60 - 108 KHz group band circuits. It contains the 34-pin V.34 connector specifications normally implemented on a modular RJ-45 connector.

V.42

An IUT-T standard protocol for error correction between modems which includes MNP up to level 4.

V.42bis

An extension of the IUT-T V.42 standard modem protocol to included compression.

VAN

Value Added Network (network)

Vannevar

A bogus technological prediction or a foredoomed engineering concept, especially one that fails by implicitly assuming that technologies develop linearly, incrementally, and in isolation from one another when in fact the learning curve tends to be highly nonlinear, revolutions are common, and competition is the rule. The prototype was Vannevar Bush's prediction of "electronic brains" the size of the Empire State Building with a Niagara-Falls-equivalent cooling system for their tubes and relays, a prediction made at a time when the semiconductor effect had already been demonstrated. Other famous vannevars have included magnetic-bubble memory, LISP machines, videotex, and a paper from the late 1970s that computed a purported ultimate limit on areal density for integrated circuits that was in fact less than the routine densities of 5 years later.

VBR

Variable bit rate (ATM)
Information that can be represented digitally by groups of bits (as opposed to streams) is characterized by a variable bit rate. Most data applications generate VBR traffic,which can tolerate delays and fluctuating throughput.

VBR-NRT - nrt-VBR

Variable Bit Rate - Non-Real Time (ATM)
One of five ATM Forum-defined service types. It is used for transmitting traffic where timing information is not critical and which is characterized by the average and peak cell rates. It is well-suited for long data packets transfers.

VBR-RT - rt-VBR

Variable Bit Rate - Real Time (ATM)
One of five ATM Forum defined service types for transmitting traffic that depends on timing information and control and which is characterized by the average and peak cell rates. It is suitable for carrying traffic such as packetized (compressed) video and voice.

VC

Virtual Circuit (network)
A connection set-up across the network between a source and a destination where a fixed route is chosen for the entire session and bandwidth is dynamically allocated on demand by the network as users have traffic to transmit. See also datagram, SVC, PVC.

Virtual Connection (network)
A connection established between end-users (source and destination), where packets are forwarded along the same path and bandwidth is not permanently allocated until it is used.

Virtual channel (network, ATM)
A term to describe unidirectional flow of ATM cells between connecting (switching or end-user) points that share a common identifier number (VCI) A VC may traverse several virtual paths.
Each physical circuit in an ATM network is pre-configured with some number of virtual paths. Each virtual path may support many virtual channels. Neither VPs nor VCs are assigned any dedicated bandwidth. Bandwidth is allocated on demand by the network as users have traffic to transmit. See VCC.

VCC

Virtual Channel Connection (ATM)
Defined as a concatenation of virtual channel links.
Virtual channels in two or more sequential physical circuits can be concatenated to create an end-to-end connection, called a VCC. A VCC is a specific instance of a SVC or PVC. A VCC may traverse one end-to-end VPC or several sequential VPCs.

VCI

Virtual Channel Identifier (ATM)
The unique numerical tag used to identify every virtual channel across an ATM network, defined by a 16-bit field in the ATM cell header. See VC, VCC, VP.

VCL

Virtual Channel Link (network)
A means of unidirectional transports of ATM cells between the point where a VCI value is assigned and the point where that value is translated or removed.

VCPI

Virtual Control Program Interface
An alternative, and incompatible method for doing the same thing as DOS Protected Mode Interface (DPMI).

VDSL

V Digital Subscriber Line (communications, protocol, network)
See also DSL.

VDU

Visual Display Unit (hardware)
A device incorporating a cathode ray tube (CRT) display, a keyboard and a serial port. A VDU usually also includes its own display electronics which store the received data and convert it into electrical waveforms to drive the CRT.
Early VDUs could only display characters in a single preset font, and these were confined to being layed out in a rectangular grid, reproducing the functionality of the paper-based teletypes they were designed to replace. Later models added graphics facilities but were still driven via serial communications, typically with several VDUs attached to a single multi-user computer. This contrasts with the much faster single bitmap displays integrated into most modern single-user personal computers and workstations.

VESA

Video Electronics Standards Association (body, standard)
An industry standards organisation created in 1989 or 1990 mostly(?) concerned with IBM compatible personal computers. The first standard it created was the 800 x 600 pixel Super VGA (SVGA) display and its software interface.
It also defined the VESA Local Bus (VLB). See also PCI.

VF

Variance Factor
It is the CRM normalized by the variance of the total cell rate over a given circuit.

VFast

28800 bps, original (working) name for V.34 standard for modem. Most implementations were incompatible with each other. It is obsolete.

VGA

Video Graphics Array (hardware)
A display standard for IBM PCs, with 640 x 480 pixels in 16 colours and a 4:3 aspect ratio. There is also a text mode with 720 x 400 pixels.
IBM technical references define the *product name* of their original VGA display board as "Video Graphics Array", in contrast to the preceding boards, the "Color Graphics Adapter" (CGA) and "Enhanced Graphics Adapter" (EGA).

Videotex

An obsolete electronic service offering people the privilege of paying to read the weather on their television screens instead of having somebody read it to them for free while they brush their teeth. The idea bombed everywhere it wasn't government-subsidised, because by the time videotex was practical the installed base of personal computers could hook up to time-sharing services and do the things for which videotex might have been worthwhile better and cheaper. Videotex planners badly overestimated both the appeal of getting information from a computer and the cost of local intelligence at the user's end. Like the gorilla arm effect, this has been a cautionary tale to hackers ever since. See also vannevar.

VIM

Vendor Independant Messaging (communications, networking)
An electronic mail API promoted by an industry group headed by Lotus Development. VIM is a competitor to Microsoft's MAPI.

Virus

(By analogy with biological viruses, via SF) A cracker program that searches out other programs and "infects" them by embedding a copy of itself in them, so that they become Trojan horses. When these programs are executed, the embedded virus is executed too, thus propagating the "infection". This normally happens invisibly to the user.
Unlike a worm, a virus cannot infect other computers without assistance. It is propagated by vectors such as humans trading programs with their friends (see SEX). The virus may do nothing but propagate itself and then allow the program to run normally. Usually, however, after propagating silently for a while, it starts doing things like writing "cute" messages on the terminal or playing strange tricks with the display (some viruses include display hacks). Many nasty viruses, written by particularly antisocial crackers, do irreversible damage, like deleting all the user's files.
In the 1990s, viruses have become a serious problem, especially among IBM PC and Macintosh users (the lack of security on these machines enables viruses to spread easily, even infecting the operating system). The production of special anti-virus software has become an industry, and a number of exaggerated media reports have caused outbreaks of near hysteria among users; many lusers tend to blame *everything* that doesn't work as they had expected on virus attacks. Accordingly, this sense of "virus" has passed into popular usage (where it is often incorrectly used to denote a worm or even a Trojan horse). Compare back door.

VLAN

Virtual Local Area Network
A network configuration in which users communicate using LAN protocols as if they were on the same physical LAN, but where they are in fact on physically separate LANs. Software and/or hardware mask the physical topology of the users and provide a logical topology which is more suitable to the users' requirements.

VML

Vector Markup Language (graphics)

Vocoder

Voice coder, speech is encoded before transmission to reduce the number of bits required to represent speech.

VOD

Video on Demand (communications)
A technology that enables the customer to remotely select and play a video, transmitted over communications links. A planned system using video compression to supply programs to viewers when requested, via ISDN or cable.

VP

Virtual Path
A term to describe a set of virtual channels (VCs) grouped together, between crosspoints (i.e. switches).
Each physical circuit in an ATM network is pre-configured with some number of virtual paths. Each virtual path may support many virtual channels. Neither VPs nor VCs are assigned any dedicated bandwidth. Virtual paths may be used to construct end-to-end connections, called VPCs.

VPC

Virtual Path Connection (ATM)
Virtual paths in two or more sequential physical circuits can be concatenated to create a logical connection, called a VPC. VPCs must be pre-configured. All Cells traversing VCs in a VPC are routed the same way.
See VPI.

VPCI/VCI

Virtual Path Connection Identifier/Virtual Channel Identifier (network)
A combination of two numbers, one for identifying the VP and one for VCI.

VPDN

Virtual Private Data Network (network, public)

VPI

Virtual Path Identifier (ATM)
The 8-bit number in an ATM UNI cell header or the 12-bit number in an ATM NNI or B-ICI cell header identifying the specific virtual path (VP) on which the cell is traversing on the current physical circuit. The ETSI version of ATM called it VCI. A virtual connection established using only the VPI is known as a virtual path connection (VPC).

VPL

Virtual Path Link (network, ATM)
The field in the ATM cell header that labels (identifies) a particular virtual path.

VPN

Virtual Private Network (network)
Network resources provided to users, on-demand, by public carriers such that the users view this partition of the network as a private network (customer-unique addressing, network management capabilities, dynamic reconfiguration, etc.).
A VPN can also be used using cryptology across Internet, each end of a connexion is controled by a firewall.
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. The advantage of the VPNs over the dedicated private networks is that the former allow a dynamic allocation of network resources.

VPT

Virtual Path Terminator (network)
A system that unbundles the VCs of a VP for independent processing of each VC.

VRC

Vertical Redundancy Check (network)
Partity check applied to a single word, not to a complete set of words.

VRML

Virtual Reality Modeling Language (language)

VRU

Voice Response Unit (telephone)
Syn IVR (Interactive Voice Response).
Equipment that prompts callers to input information about their accounts or about the nature of their call. For example, a VRU might be a recording that instructs, "Please enter your account number using your touch-tone phone," or "If you would like to speak with a sales agent, please press one". The VRU feeds such information into the ACD so that calls are correctly routed. VRUs can also feed information to agents in the form of screen pops. VRUs are sometimes called Interactive Voice Response (IVR) units.

VS/VD

Virtual Source/Virtual Destination (ATM)

VSA

Virtual Scheduling Algotithm (ATM)
GCRA equivalent algorithm used by ITU UPC and NPC specifications.

VSAT

Very Small Aperture Terminal (communications)
A kind of ground station used to contact a communications satellite such as INMARSAT.

VT

Virtual Tributary (network, ATM)
A mechanism of capacity allocation in SONET that subdivides a synchronous payload envelope into lower-bit-rate envelopes within the SONET signal.

VTAM

Virtual Telecommunications Access Method
Access method IBM SNA architecture.

VTOA

Voice Telephony Over ATM (ATM)
ATM Forum specification concerning voice telephony over ATM.

VTP

Virtual Terminal Protocol
OSI's remote terminal protocol.

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