R0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
- 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
- RAM: See Random Access
- 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
- Real Time: Operating mode that allows immediate interaction
with data as it is created, as in a process-control system or computer aided
- 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
- 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
- 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
- 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
- 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
- Resonance: An ac circuit condition in which inductive &
capacitive reactances interact to cause a minimum or maximum circuit
- Resource: Something that can be shared over a LAN,
inclusive but not limited to printer, modems, disk drives &
- 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
- Response Time: The time required between transmission of the
last character of a message & reception of the first reply
- 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
- 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.
: See Radio Frequency
- RFC: Request for
- RG-58: Coaxial cable with 50 ohm impedance used by
- RG-62: Coaxial Cable with 93 ohm impedance used by
- RG/U: RG is the military designation for coaxial cable, & "U"
stands for "general utility".
- RI: See Ring
- Ribbon Cable: A flat cable of individually insulated
conductors lying parallel & held together by means of adhesive or woven textile
- 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.
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
- Ring Topology: A network topology in which nodes are
connected to a closed loop. no terminators are required because there are no
- RIP: See Routing Information
- RISC: See Reduced Instruction Set
- Riser: Application for indoor cables that passes
between floors. It is normally a vertical shaft or space.
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.
- ROM: See Read Only
- 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
- 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.