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 It is 11:34 PST on Monday 03/01/2021

"V" Networking Definitions & Concepts...

VAX OSI Transport Service (VOTS) .. to .. VRML (Virtual Reality Modeling

# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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VAX OSI Transport Service (VOTS):
Vector Graphics:
Vertical Wiring:
VGA:
View (Database)
Virtual Circuit
Virtual Circuit Switching
Virtual Memory System (VMS):
Virtual Reality Modeling Language (VRML):
Volume:
Volume Catalog:
Volume ID:
Volume Signature:



Value: (UML)

An element of type domain.

Variable: (OO)

A property of an object that contains a data value describing the object.

VAX OSI Transport Service (VOTS):

In the OSI Reference Model, a transport level protocol used on Digital Equipment Corporation (DEC) machines. VOTS can be used in local-area or wide-area networks.

Vector Graphics:

Vector graphics describes the use of geometrical primitives such as points, lines, curves, and polygons to represent images in computer graphics. It is used by contrast to the term raster graphics, which is the representation of images as a collection of pixels (dots), bit mapped.

Virtually all current output devices must ultimately translate vector representations of an image to a raster format (bit mapped), but when working with vector graphics such a transformation is only done at the time the image is actually required and may be done completely differently depending on the device at which the rendering is to be targeted at. In the 1970's and 1980's, special vector graphics systems were available, in which the electron beam of the CRT display monitor was steered directly to trace out the shapes required. These systems allowed very high-resolution line art to be displayed without the (at the time) huge memory requirements that an equivalent-resolution raster system would have had. Vector plotters used in technical drafting still draw vectors directly to paper.

The term is mainly used in the context of two-dimensional graphics. Virtually all modern 3-d rendering is done using extensions of 2-d vector graphics techniques.

Vector graphics are simply another type of image that can be displayed on your display screen. Much like the GIF and JPEG formats you are used to seeing and working with, vectors have their own advantages and disadvantages as a way of delivering images on Web pages. The advantages, however, are getting more and more enticing.

To understand why vectors are a good thing, let's take a crash course in how images work on a computer screen. Most of the graphics you see on the Web today are bitmaps; that is, they are made up of a set of pixels, each one a different color, combining into the patterns that make up the image. When you create a bitmap, you use a graphics application to essentially decide which pixels will be which color and what the dimensions of the image should be. Simple enough. But what happens if you want to change the size of the image? Well, you either start over and make a new graphic, or you stretch it - with generally unpleasant results.

Enter the vectors. Rather than assigning colors to pixels, a vector graphic application lets you draw with lines and shapes. Essentially, a vector graphic is a series of commands that might dictate a line's direction, thickness, and color, which gets rendered on the screen later. The benefits are obvious: The files are very small (each pixel need not be accounted for), they can be resized to any proportion, and they are eminently flexible because they can simply be re-rendered at any point.

Vertex: (UML)

A source or a target for a transition in a state machine. A vertex can be either a state or a pseudo-state.

Vertical Partitioning: (Database)

Splitting the columns (attributes) of a table into multiple tables to improve retrieval performance.

Vertical Wiring:

In a structured wiring system, the vertical wiring is the cable that stretches from the wiring closet on each floor to the main equipment room in the basement or first floor of the building. In contrast, the horizontal wiring is the cable that runs from a telecommunication wiring closet to each of the workstations on a floor of a building.

Video Graphics Array (VGA):

Video Graphics Array (VGA) is a computer display standard marketed in 1987 by IBM. VGA belongs to a family of earlier IBM video standards and largely remains backward compatible with them. VGA can be seen as an enhancement of and sucessor to the previous EGA graphics adapter.

As with most IBM hardware the VGA was extensively cloned by other manufacturers. While the VGA has been obsolete in original form for some time it was the last IBM standard that the majority of clone manufacturers decided to follow, making it even today the only standard graphics interface that can be relied on to be present on the PC architecture. VGA was technically superseded by IBM's XGA standard, in reality it was superseded by the numerous extensions to the VGA by clone manufactuers and came to be known as Super VGAs.

Even today, VGA remains a relavant graphics standard. It forms the "lowest common denominator" that all PC graphics cards need to support prior to a device-specific driver being loaded. On Windows machines, the Microsoft Windows splash screen appears while the machine is still operating in VGA mode, which is the reason that this screen always appears in reduced resolution and color depth than following screens.

The VGA specifications are as follows:

  • 256KByte Video RAM
  • 16 colour or 256 colour modes
  • 262144 colour palette
  • Selectable 25Mhz or 28Mhz master clock
  • Maximum of 720 horizontal pixels
  • Maximum of 480 lines
  • Refresh rates at up to 70 Hz
  • 4 video planes
  • Hardware smooth scrolling support
  • Some 'Raster Ops' support
  • Barrel shifter
  • Split screen support
  • Soft fonts

The VGA supports both All Points Addressable graphics modes, and Alphanumeric Text modes. Standard graphics modes are:

  • 640x480 in 16 colors
  • 640x400 in 16 colors
  • 320x200 in 16 colors
  • 320x200 in 256 colors (Mode 13h)

An undocumented, but popular 256 colour mode called Mode X was used to make available programming techniques and graphics resolutions not possible in the standard Mode 13h. This was a trade off for extra complexity and performance loss in some types of graphics operations.

Standard alphanumeric text modes for the VGA are 80x25 and 40x25 text cells. Each cell may choose from one of 16 available colours for its foreground and 8 colours for the background. The character may also be made to blink, or at the expense of the blinking option, the background may be selected from 16 colours.

As well as the standard modes the VGA supports many of the modes of its predecessors the EGA, CGA, MDA and due to its configurable nature, un-documented modes.

View: (Database)

A named query store in a data dictionary that is used to create a virtual table whenever a user includes the name of the view in a data access request.

View: (Satellite Communications)

In satellite communications, the quality or degree of visibility of a satellite to a ground station; i.e., the degree to which the satellite is sufficiently above the horizon and clear of obstructions so that it is within a clear line of sight by an Earth terminal.

Note: A pair of satellite Earth terminals has a satellite in mutual view when both have unobstructed line-of-sight contact with the satellite simultaneously.

View: (UML)

A projection of a model seen from a given perspective or vantage point and omitting entities that are not relevant to that perspective. A virtual table that, from the user's perspective, behaves exactly like a typical table but has no independent existence of its own.

View Element: (UML)

A view element is a textual and/or graphical projection of a collection of model elements.

View Projection: (UML)

A projection of model elements onto view elements. A view projection provides a location and a style for each view element.

Virtual Circuit (VC):

In long-distance communications, a virtual circuit is a temporary connection between two points. This type of circuit will appear as a dedicated line to the user, but will actually be using packet switching to accomplish transmissions. The virtual circuit is maintained as long as the connection exists. A different virtual circuit may be established each time a call is made.

Virtual circuits are used in contrast to leased lines, in which a dedicated connection between two particular points is always available. X.25 and frame relay both use virtual circuits.

In the X.25 environment, a virtual circuit is a logical connection between a DTE (computer) and a DCE (digital service unit, modem, or multiplexer). This type of connection can be a switched virtual circuit (SVC) or a permanent virtual circuit (PVC). The SVC can connect to a different DTE at the other end each time. The PVC always connects to the same DTE at the other end.

Virtual Circuit Switching (VCS):

Is a temporary connection between end stations. Connections last only as long as necessary and are disconnected when the session is complete. The virtual circuit must be set up just prior to data transfer. Some packet-switching services provided by the carriers allow customers to dynamically define a VCS as required.

Virtual Class (OO):

A class from which no objects can be created.

Virtual LAN (VLAN):

A logical network built out of sub-networks of workgroups that are established through intelligent software on switches and routers and that are independent of the physical network topology.

Virtual Memory System (VMS):

A proprietary operating system used by Digital Computer for its VAX (Virtual Address Extension) computers.

By and large, the VMS TCP/IP internet network facilities are modeled after the UNIX ones. (Indeed, wherever possible, they borrowed the UNIX code and adapted it.) But VMS is different for a couple of reasons:

  • There is no single dominant version of TCP/IP for VMS. About five versions exist, all from different vendors, and all provide slightly different services. Whoever runs the VMS machine will have chosen one of them already, so you have what you have. They all work perfectly well but have slightly differnt warts.
  • VMS has its own native network (DECnet) and its own file-management system (RMS). In many places (notably mail), VMS assumes that when you talk about a network, you mean DECnet, and you have to say specifically that, no, you mean the Internet instead.
Virtual Path Identifier/Virtual Channel Identifier (VPI/VCI):

A code in an ATM (Asynchronous Transfer Mode) cell that enables the cell to reach the intended output interface.

Virtual Table: (Database)

A table in a relational database that exists only in main memory.

Visibility: (UML)

An enumeration whose value (public, protected, package, or private) denotes how the model element to which it refers may be seen outside its enclosing namespace.

  - private
  + public
  # protected
  ~ package
Volume:

A file storage unit. Each disk attached to an AppleTalk file server is considered a volume, although some disks may contain multiple volumes.

Volume Catalog:

A tree-structured catalog of the files and directories on a volume.

Volume ID:

A session-unique value assigned by a file server to each of its volumes; AFP (AppleTalk File Protocol) calls use the Volume ID to specify the desired volume.

Volume Signature:

A 2-Byte field in AFP (AppleTalk File Protocol) calls that identifies the valume type; volumes are of three possible types: flat, fixed Directory ID, or variable Directory ID.

Virtual Reality Modeling Language (VRML):

VRML is an acronym for the Virtual Reality Modeling Language. Using VRML one can craft their own three-dimensional virtual worlds. In which one can make virtual rooms, buildings, cities, mountains, and planets to name a few. Basically, the Virtual Reality Modeling Language (VRML) is a standard language for describing interactive 3-D objects and worlds delivered across the Internet. These virtual worlds can be filled with virtural furniture, cars, people, spececraft, or anything else that can be dreamed up. The imagination is the only limit.

Perhaps the most exciting feature of VRML is its ability to link virtural worlds together on the World Wide Web (WWW or the Web. Using linking, one can connect a door in one world to another VRML world described elsewhere on the Web. Doors in that world can link back to the prevoius world or to other worlds on the Web. VRML linking puts the entire Internet at ones fingertips, enabling one to explor the network as if wondering through a vast universe, stepping between worlds through door after mouse hole after gateway after mirror after portal after worm hole.

The VRML Specification:

VRML's features are defined by a public VRML specification document available at the VRML Repository. VRML is a rapidly evolving standard with a tremendous amount of support from the software community. As VRML evolves, so will the VRML specification document. One is encouraged to check the VRML Repository at the Web3D Repository for the latest information on the VRML specification.




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Networking "V" Definitions and Concepts

robert.d.betterton@rdbprime.com


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This page was last updated on 09/18/2005
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