Glossary 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
- 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. Riser: Application for
indoor cables that passes between floors. It is normally a vertical shaft or
- 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.
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
- 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
- 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.
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
- 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 Chord: A chord having specially treated
insulation or jacket so that it will react like a spring. Retractability may be
added to all or part of a chord'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
- RJ11: Four-wire modular connectors for phone
- 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
- 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
- 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
- RPC: See Remote Procedure
- 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.
- 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 introduces 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.