Multimedia Glossary: R

RARP

Reverse Address Resolution Protocol

This protocol makes life easier to change IP addresses on machines. For all the machines on a network to see one another, they must know the others' IP addresses. If the IP address of one machine changes, the change must be done on each of the other machines. This would take a million years, so enters RARP which makes it possible to manage changes centrally and broadcast them to the other machines. RARP looks for an IP address when given a hardware address (the opposite of ARP).

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Raster and raster graphics

Also see bitmap graphics.

On CRT (cathode ray tube) and LCD (liquid crystal display) monitors images are displayed on a raster along X- and Y-axes. A raster graphic is an image displayed on this raster grid. When reference is made to the image file that is displayed on the raster, it is called a bitmap file as the image information bits are mapped onto the raster.

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RFC

Request for Comment

An RFC is a documents that states protocol standards, proposed changes, information bulletins about the internet. The name is somewhat of a misnomer in some cases as an RFC document often serves as the standard which is already being accepted as valid from a certain date until it is officially changed. An RFC may also be an explanation of an existing practice.

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Request for Comment

See RFC

Reverse Address Resolution Protocol

See RARP

RGB

RGB color stands for "Red Green Blue" (see color) and is an additive color mechanism. This 10-base system is used in CSS together with HTML to assign color to elements. Here is a table with the basic RGB values:

The basic Hex-DEC color palette

		Name	Hex-DEC Value			Name	Hex-DEC Value
		Aqua	"#00FFFF"			Navy	"#000080"
		Black	"#000000"			Olive	"#808000"
		Blue	"#0000FF"			Purple	"#800080"
		Fuchsia	"#FF00FF"			Red	"#FF0000"
		Gray	"#808080"			Silver	"#C0C0C0"
		Green	"#008000"			Teal	"#008080"
		Lime	"#00FF00"			White	"#FFFFFF"
		Maroon	"#800000"			Yellow	"#FFFF00"

Also see sRGB

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Rollover image

A rollover image is used in the context of navigation where an image button, that serves as a link elsewhere, changes into a different image because of some or other associated pointer behaviour (e.g. mouse down).

Rotoscoping

A rotoscope is an animation stand used to project a sequence of action frames against a surface. An artist could then trace a set of animation frames. For example, the background of the scene would be projected, and the actor is drawn, or edited onto this background -- i.e. compositing. This process can now be done with computers and a rotoscope is no longer used. The term rotoscoping is now used for the doctoring film or animation sequences frame-by-frame.

Router

A router functions like a traffic officer, directing the flow of data to targets. It receives a packet of data, reads the address, and passes it on to the next machine in the line.

In the beginning of the internet routers were typically in a separate box so as to reduce the load on the web (i.e. HTTP) server. However, router software may reside on the HTTP server.

A router operates at the network level of the OSI model. For each protocol there would be a different router as they are protocol dependent. However, routers do not bother about different network topologies and can therefore be used to pass data along different networks such as Ethernet and Token Ring.

A router relates to a bridge and a gateway. A bridge allows any frame that is allowed to be passed on to a segment, while a router only allows addressed frames. A router is thus more intelligent than a bridge. However, routers work much harder than bridges, and therefore their throughput is much lower.

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