Glossary R

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Raceway: Any channel designed for holding wires or cables (conduit, electrical metallic tubing, sleeves, slots, underfloor raceways, cellular floors, surface raceways, wireways, cable troughs, busways, auxiliary gutters & ventilated flexible cableway).
Radio Frequency: (RF) The frequencies in the electromagnetic spectrum that are used for radio communications.
Radio Frequency Interference: (EFI/RFI) A form of "noise" on data transmission mediums that can reduce data integrity & increase transmission errors.
RAM: See Random Access Memory
RAM base address: Starting address for memory dedicated to a specific task.
Random Access Memory: (RAM) Memory in which data is temporarily stored for processing.
RARP: See Reverse Address Resolution Protocol
RD: See Receive Data
Read Only Memory: (ROM) Memory chips that store data or software.
Real Mode: CPU mode in which applications have direct access to the physical memory of the computer.
Real Time: Operating mode that allows immediate interaction with data as it is created, as in a process-control system or computer aided system.
Receive Data: (RD) An incoming signal in the RS232-C DTE-DCE interface
Receiver: An electronic package that converts the optical signal to an electrical signal. See also Photo Detector.
Record Locking: A method of managing shared data on a network by preventing more than one user from accessing the same segment of data at the same time.
Redirector: An application that intercepts requests for resources local to a node on the network & redirect those requests elsewhere on the network.
Reduced Instruction Set Computing: (RISC) Internal computing architecture where processor instructions are pared down so that most can be performed in a single processor cycle, theoretically improving computing efficiency.
Redundancy: In data transmission the portion of a message's gross information content that can be eliminated without losing essential information also, duplicate facilities.
Reflection: The change in direction (or return) of waves striking a surface. For example, electromagnetic energy reflections can occur at an impedance mismatch in a transmission line, causing standing waves.
Refraction (Fiber Optic): The bending of lightwaves or rays as they go from one material to another due to the differences in velocities in the material. Refractive Index: The ratio of light velocity in a vacuum to its velocity in the transmitting medium.
Reliable Transport: A transport layer, such TCP, which guarantees reliable, in-sequence delivery of all data. Contrast to "unreliable" or best effort transport which has very lower overhead, but leaves reliability mechanisms to the upper layer.
Remote: A term used to describe network devices that are managed or controlled from a network system other than the system to which they are directly connected.
Remote Access: A term which describes remote LAN connectivity of individual users, such as home offices, traveling employees & small branch locations. Communication is possible over a selection of WAN services, including asynchronous dial-up lines to 115.2 Kbps, ISDN, X.25 & Frame Relay.
Remote Bridge: A bridge located on a network system separate from the host system.
Remote Control Access: A type of remote access to a network where a remote PC dials into & takes control of a PC on a network. Only screens & keyboard updates are passed over the connection.
Remote Login: A specific feature which allows authorized users of one TCP/IP system to log into another over a network & interact as if directly connected to each other.
Remote Node Access: A type of remote access to a network where a remote PC or workstation dials into & fully functions as an end node on the network while also utilizing the processing power of the remote PC; processing is done on the local computer.
Remote Procedure Call: (RPC) A protocol governing the method with which an application activates processes on other nodes & retrieves the results.
Remote Repeater: A repeater located on a network system other than the host system.
Repeater: A device that increases the length of a network by regenerating the signal.
Request To Send: (RTS) A modem control signal sent from the DTE to the modem which tells the modem that the DTE has data to send.
Resistance: In dc circuits, the opposition a material offers to current flow, measured in Ohms, In ac circuits, resistance is the real component of impedance, & may be higher than the value measured at dc.
Resonance: An ac circuit condition in which inductive & capacitive reactances interact to cause a minimum or maximum circuit impedance.
Resource: Something that can be shared over a LAN, inclusive but not limited to printer, modems, disk drives & directories.
Resource Sharing: A mode of operation in which certain resources within a system may be shared by multiple DTE's. The resources may be hardware (i.e., printer, disk storage) or software (application programs, data files).
Response Time: The time required between transmission of the last character of a message & reception of the first reply character.
Retractile Cord: A cord having specially treated insulation or jacket so that it will react like a spring. Retractability may be added to all or part of a cord's length.
Retransmissive Star: In optical fiber transmission, a passive component that permits the light signal on an input fiber to be retransmitted on multiple output fibers to near the melting point; used mainly in fiber based local area networks also, star coupler.
Return Loss: Noise or interference caused by impedance discontinuities along the transmission line at various frequencies. Return loss is expressed in decibels.
Reverse Address Resolution Protocol: (RARP) A TCP/IP protocol governing the translation of a DLC (Data-Link Control) address to an IP (Internet Protocol) address.
RF : See Radio Frequency
RFC: Request for Comment.
RG-58: Coaxial cable with 50 ohm impedance used by Thinnet
RG-62: Coaxial Cable with 93 ohm impedance used by ARCnet
RG/U: RG is the military designation for coaxial cable, & "U" stands for "general utility".
RI: See Ring Indicator
Ribbon Cable: A flat cable of individually insulated conductors lying parallel & held together by means of adhesive or woven textile yarn.
Ring: A LAN network where workstations are connected to form a loop. The method of access control is token passing, where data is sent from workstation to workstation around the loop in the same direction until it reaches its destination.
Ring Conductor: A telephony term used to describe one of the two conductors in a cable pair used to provide telephone service. This term was originally coined from its position as the second (ring) conductor of a tip-ring 0sleeve switchboard plug.
Ring Indicator: (RI) A control signal in the RS232-C DTE-DCE interface. This signal indicates that a remote DTE intends to establish a communication like with local DTE. It performs the same function as the ringing on a common telephone set.
Ring Topology: A network topology in which nodes are connected to a closed loop. no terminators are required because there are no connected ends.
RIP: See Routing Information Protocol
RISC: See Reduced Instruction Set Computing
Riser: Application for indoor cables that passes between floors. It is normally a vertical shaft or space.
RJ11: Four-wire modular connectors for phone lines.
RJ45: Eight-wire modular connectors for StarLAN networks & some phone lines.
RMON: The remote monitoring MIB, which allows a network monitoring device to be configured & read from remote locations.
RMS: Root-mean-square.
ROM: See Read Only Memory
Route discovery: Process through which a router can learn LAN topology by passing information about its address & the LASNs it connects & receiving the same information from others.
Router: Hardware/software products that receive network layer datagrams & forward them to their destinations.
Routing: The process of selecting the correct circuit path for a message.
Routing Information Protocol: (RIP) An interior Gateway Protocol used by TCP/IP to exchange routing information on a small computing network.
RPC: See Remote Procedure Call
RS232: A standard interface connection that provides for only modest transmission rates & is often used with modems. RS232 cables have 25-pin, D-type connectors on either end. The most popular connector on a PC is 9-pin.
RS422: An EIA recommended standard for cable lengths that extended the RS232 50 foot limit. Although introduced as a companion standard with RS449, RS422 is most frequently implemented on unused pins of DB25 (RS232) connectors. Electrically compatible with CCITT recommendation V.11.
RS423: An EIA recommended standard for cable lengths that extended the RS232 50 foot limit. Although introduced as a companion standard with RS449, RS423 is not widely used. Electrically compatible with CCITT recommendation V.10.
RS449: An EIA recommended standard for the mechanical characteristics of connectors; introduced as companion standard to RS422 & RS423 standards. Specifies two connectors a 37 pin connector & a 9-pin connector. This is not widely used.
RTS: See Request To Send
Rubber: (wire insulation) A general term used to describe wire insulation's made of thermosetting elastomers, such as natural or synthetic rubbers, neoprene, Hypalon, butyl rubber, & others.

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