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Random Access Memory, RAM

It is memory that can be read from or written to by a computer or other devices.  Information stored in RAM is lost when the computer is turned off.

Real-Time Control Protocol, RTCP

RTCP provides support for real-time conferencing of groups of any size within an intranet. This support includes source identification and support for gateways like audio and video bridges as well as multicast-to-unicast translators.  It offers quality-of-service feedback from receivers to the multicast group as well as support for the synchronization of different media streams. 

Real-Time Transport Protocol, RTP

RTP is an Internet protocol for the transport of real-time data, e.g. audio and video. It can be used for media-on-demand as well as interactive services such as Internet telephony. 

Real Time Streaming Protocol, RTSP

RTSP is a control protocol, and a starting point for negotiating transports such as RTP, multicast and Unicast, and for negotiating codecs.  RTSP can be considered a “remote control” for controlling the media stream delivered by a media server. RTSP servers typically use RTP as the protocol for the actual transport of audio/video data.

Receiver

A unit that converts an RF signals to another type of signal (e.g. radio, video, television).  Also refers to an electronic package that converts light energy to electrical energy in a fiber optic system.

Recording Resolution

The more pixels used to represent an image, the closer the result can resemble the original.  The number of pixels in an image is sometimes called the resolution.  Pixel counts can be expressed as a single number, as in a "three-megapixel" digital camera, which has a nominal three million pixels, or as a pair of numbers, as in a "640 by 480 display", which has 640 pixels from side to side and 480 from top to bottom (as in a VGA display), and therefore has a total number of 640 × 480 = 307,200 pixels or 0.3 megapixels.  The pixels, or color samples, that form a digitized image (such as a JPEG file used on a web page) may or may not be in one-to-one correspondence with screen pixels, depending on how a computer displays an image. An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels.  One could refer to it as 2048 by 1536 or a 3.1-megapixel image.  As the megapixels of a camera increase so does the ability of a camera to produce a larger image; a 5 megapixel camera is capable of capturing a larger image than a 3 megapixel camera.  Larger monitor screens usually have higher screen resolution, measured in pixels.

Refresh Rate

The refresh rate of a monitor is the maximum number of times the image on screen can be "drawn" per second, measured in Hertz.  The most common refresh rate for today's Televisions are 60hz for NTSC-based systems and 50hz for PAL-based systems.

Remote Control

A transmitting and receiving of signals for controlling remote devices such as pan and tilt units, lens functions, wash and wipe control and similar.

Resistance

In DC circuits, the opposition a material offers to current flows, measured in ohms.  In AC circuits, resistance is the real component of impedance, and may be higher than the value measured at DC.

Resolution

Image resolution is a measure of how much detail a digital image can hold: the greater the resolution, the greater the level of detail. Resolution can be specified as the number of pixel-columns (width) by the number of pixel-rows (height), e.g. 320x240.  Alternatively, the total number of pixels (usually in megapixels) in the image can be used. In analog systems it is also common to use other format designations, such as CIF, QCIF, 4CIF, etc.

Retractile Cord

It is a cord having specially treated insulation or jacket so that it will retract like a spring.  Retractability may be added to all or part of a cord’s length.

Return Loss

It is a measure of signal reflections from a cable or device with a fixed, standard reference impedance on the measuring equipment.  It is usually expressed in decibels (dB).

RG-58

A coaxial cable designed with 50-ø [impedance; therefore, not suitable for CCTV]. It is very similar to RG-59, only slightly thinner.

RG-59

A type of coaxial cable that is most common in use in small to medium-size CCTV systems.  It is designed with an impedance of 75-ø [It has an outer diameter of around 6 mm and it is a good compromise between maximum distances achievable (up to 300 m for monochrome signal and 250 m for color) and good transmission.

RGB

The red, green & blue, the black is simulated colour.  CMYK is the four primary colours.

RG/U

RG is the abbreviation for radio guide, a military designation for a coaxial cable, and U stands for universal.

RJ-45

Modular telecommunications connector.

RoHS

Restriction on Hazardous Substances, RoHS refers to the European Union directive 2002/95/EC (27-JAN-2003) which bans the use of certain substances as of July 2006.  The use of heavy metal substances, Lead and its compounds, Polybrominated Biphenyls (pbbs) and their ethers/oxides (PBDEs, PBBEs) are primary concern in electronic products.  In cable, primary concern are namely: Abestos and its compounds, Cadmium and its compounds, Chromium VI and its compounds, Lead and its compound, Mercury and its compound, and Polybrominated Biphenyls (pbbs) and their ethers/oxides (PBDEs, PBBEs).

ROM

An acronym for Read-Only Memory, a semiconductor circuit into which code or data is permanently installed by the manufacturing process. ROM contains instructions or data that can be read but not modified.

Router
A device that determines the next network point to which a packet should be forwarded on its way to its final destination. A router creates and/or maintains a special routing table that stores information on how best to reach certain destinations.  A router is sometimes included as part of a network switch.

RS-232

A format of digital communication where only two wires are required.  It is also known as a serial data communication.  The RS-232 standard defines a scheme for asynchronous communications, but it does not define how the data should be represented by the bits, i.e., it does not define the overall message format and protocol.  It is very often used in CCTV communications between keyboards and matrix switchers or between matrix switchers and PTZ site drivers.  The advantage of RS-232 over others is its simplicity and use of only two wires.

RS-422

RS-422 is a serial data communication protocol that specifies 4-wire, full-duplex, differential line, multi-drop communications. It provides balanced data transmission with unidirectional/non-reversible, terminated or non-terminated transmission lines. RS-422 does not allow multiple drivers, only multiple receivers. Maximum recommended range is 4,000 feet (1200 meters). Maximum recommended baud rate is 10Mbit/s.

RS-485

This is an advanced format of digital communications compared to RS-422.  The major improvement is in the number of receivers that can be driven with this format, and this is up to 32.