QOS - Quality of Service is a catchphrase for a network that can transport data without losing cells, with predictable end-to-end delay, with real-time delivery of data once the connection is completed. High-quality multimedia over a network, whether in real-time or merely playing audio or video files from a server, requires a network that can deliver QOS. Protocals such as ATM (Asynchronous Transfer Mode) are designed to deliver multiple levels of QOS. Attempting to deliver QOS using IP requires additional services such as RSVP (Resource Reservation Protocol), which allows bandwidth to be reserved and to be supported on intermediate devices such as routers.  

Radiolink - Network transmission using radio technology, such as microwave or infrared technology. 

RBOC - (regional Bell operating company) is a term describing one of the U.S. regional telephone companies (or their successors) that were created as a result of the breakup of American Telephone and Telegraph Company (AT&T, known also as the Bell System or "Ma Bell") by a U.S. Federal Court consent decree on December 31, 1983. 

Registered Jack - RJ (registered jacks, sometimes described as RJ-XX) is a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. Federal Communications Commission (FCC). 

Refractive index - Numerical value that describes the refraction of light when it passes through the boundary of two different materials.

Regenerator - Device that restores a degraded digital signal for continued transmission; also called a repeater.

Relay - A device used in electromechanical switches that uses a current to close a mechanical switch.

Remote access -The ability to access a network from a location not directly connected to the network site.

Repeater - Device that restores a degraded digital signal for continued transmission; also called a regenerator.

Resolution - A measure of sharpness or clarity on a monitor.

Reverse battery signaling - Method of DC signaling based on the signal's changing polarity of the voltage in the circuit.

Ring - A point of electrical contact in a manual switchboard plug. It connects to one of the two wires in a two-wire transmission. The other point of contact is termed the tip. Although the manually switched line is obsolete, the terms are still used for line assignment purposes. Routed on a trunk-by-trunk basis through a matrix of incoming and outgoing trunks. 

RGB - Red-Green-Blue picture display format.

RJ-11 - The plastic four-wire jack on a phone wire.

RJ-45 - The plastic eight-wire ISDN jack.

Room  based videoconferencing - Videoconferencing using a sophisticated system. Appropriate for large groups.

Router - A protocol-dependent device that connects similar and dissimilar LANs and also WANs.

RS-232 - Generic 25-pin data interface used for serial byte data communication (same as V.24). An EIA-specified physical interface with associated electrical signaling between DCE and DTE. The most commonly employed interface between computer devices and modems.

RS-366 - Generic dialing interface ( An EIA interface standard for autodialing).

RS-449 - Generic 37-pin fast differential data interface.

RS-530 - Interface using DB-25 connector, but for higher speeds than RS-232. Has balanced signals (like EIA-422) except for three maintenance signals which are EIA-423.

RTP/RTCP - Real-Time Protocol/Real-Time Control Protocol. Protocols that provides real-time data delivery characteristics over IP.

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