Table of Contents




Research on Advanced Communications in Europe. Project sponsored by the EC for the development of broadband networking capabilities.

race condition ranging

The process of acquiring the correct timing offset such that the transmissions of a cable modem are aligned with the correct mini-slot boundary.

radio frequency

See Request For Comments. Document series used as the primary means for communicating information about the Internet. Some RFCs are designated by the IAB as Internet standards. Most RFCs document protocol specifications such as Telnet and FTP, but some are humorous or historical. RFCs are available online from numerous sources..

radio frequency interference

See RFI.


registration, admission, and status protocol. Protocol used in the H.323 protocol suite for discovering and interacting with a Gatekeeper.


remote defect identification. In ATM, when the physical layer detects loss of signal or cell synchronization, RDI cells are used to report a VPC/VCC failure. RDI cells are sent upstream by a VPC/VCC endpoint to notify the source VPC/VCC endpoint of the downstream failure.


Remote Dial-In User Service. Database for authenticating modem and ISDN connections and for tracking connection time.


random-access memory. Volatile memory that can be read and written by a microprocessor.

random-access memory

See RAM.

Rapid Transport Protocol

See RTP.


Réseaux Associés pour la Recherche Européenne. Association of European universities and research centers designed to promote an advanced telecommunications infrastructure in the European scientific community. RARE merged with EARN to form TERENA. See also EARN and TERENA.


Reverse Address Resolution Protocol. Protocol in the TCP/IP stack that provides a method for finding IP addresses based on MAC addresses. Compare with ARP.

rate enforcement

See traffic policing.

rate queue

In ATM, a value associated with one or more virtual circuits that defines the speed at which an individual virtual circuit transmits data to the remote end. Each rate queue represents a portion of the overall bandwidth available on an ATM link. The combined bandwidth of all configured rate queues should not exceed the total available bandwidth.


regional Bell holding company. One of seven regional telephone companies formed by the breakup of AT&T. RBHCs differ from RBOCs in that RBHCs cross state boundaries.


regional Bell operating company. Seven regional telephone companies formed by the breakup of AT&T. RBOCs differ from RBHCs in that RBOCs do not cross state boundaries.


remote copy protocol. Protocol that allows users to copy files to and from a file system residing on a remote host or server on the network. The rcp protocol uses TCP to ensure the reliable delivery of data.

rcp server

Router or other device that acts as a server for rcp. See also rcp.


Request Disconnect

read-only memory

See ROM.

Real Time Streaming Protocol


Real-time Transport Protocol

See RTP.


The putting back together of an IP datagram at the destination after it has been fragmented either at the source or at an intermediate node. See also fragmentation.


Interface hardware device that interconnects between a fax device and a Public Switched Telephone Network (PSTN) network. A redialer is used to forward a dialed number to another destination. Redialers contain a database of referral telephone numbers. When the user dials a specific number, the redialer collects the dialed digits and matches them to a listing in its database. If there is a match, the redialer dials the referral number (transparent to the user) and forwards the call to the referral number.


Part of the ICMP and ES-IS protocols that allows a router to tell a host that using another router would be more effective.


Software that intercepts requests for resources within a computer and analyzes them for remote access requirements. If remote access is required to satisfy the request, the redirector forms an RPC and sends the RPC to lower-layer protocol software for transmission through the network to the node that can satisfy the request.


Allowing routing information discovered through one routing protocol to be distributed in the update messages of another routing protocol. Sometimes called route redistribution.


1. In internetworking, the duplication of devices, services, or connections so that, in the event of a failure, the redundant devices, services, or connections can perform the work of those that failed. See also redundant system.

2. In telephony, the portion of the total information contained in a message that can be eliminated without loss of essential information or meaning.

redundant system

Computer, router, switch, or other system that contains two or more of each of the most important subsystems, such as two disk drives, two CPUs, or two power supplies.

regional Bell holding company


regional Bell operating company


Registration, Admission, and Status (RAS) protocol

This is the protocol used between endpoints and the gatekeeper.

registered jack connector

See RJ connector.


OSI terminology for a device that connects two or more networks or network systems. A data link layer (Layer 2) relay is a bridge; a network layer (Layer 3) relay is a router. See also bridge and router.

relative rate

See RR.

Reliable SAP Update Protocol

See RSUP in the "Cisco Systems Terms and Acronyms" section.


Ratio of expected to received keepalives from a link. If the ratio is high, the line is reliable. Used as a routing metric.


The event of a Cisco router rebooting, or the command that causes the router to reboot.

remote bridge

Bridge that connects physically disparate network segments via WAN links.

remote copy protocol

See rcp.

remote defect identification

See RDI.

remote job entry

See RJE.

remote login

See rlogin.

Remote Monitoring


Remote Operations Service Element


remote-procedure call

See RPC.

remote shell protocol

See rsh.

remote source-route bridging


rendezvous point

Router specified in PIM sparse mode implementations to track membership in multicast groups and to forward messages to known multicast group addresses. See also PIM sparse mode.


Device that regenerates and propagates electrical signals between two network segments. See also segment.


Process of keeping a copy of data, either through shadowing or caching. See caching and shadowing.

Request For Comments

See RFC.

Request To Send

See RTS.

request/response unit

See RU.

required visual inspection

See RVI.

Research on Advanced Communications in Europe


Réseaux Associés pour la Recherche Européenne


Resource Reservation Protocol


Reverse Address Resolution Protocol


Reverse Path Forwarding

See RPF.


radio frequency. Generic term referring to frequencies that correspond to radio transmissions. Cable TV and broadband networks use RF technology.


Request For Comments. Document series used as the primary means for communicating information about the Internet. Some RFCs are designated by the IAB as Internet standards. Most RFCs document protocol specifications such as Telnet and FTP, but some are humorous or historical. RFCs are available online from numerous sources.


radio frequency interference. Radio frequencies that create noise that interferes with information being transmitted across unshielded copper cable.


Remote File System. Distributed file system, similar to NFS, developed by AT&T and distributed with their UNIX System V operating system.


request for proposal.


regional holding company.


Routing Information Field. Field in the IEEE 802.5 header that is used by a source-route bridge to determine through which Token Ring network segments a packet must transit. A RIF is made up of ring and bridge numbers as well as other information.


Routing Information Identifier. Bit used by SRT bridges to distinguish between frames that should be transparently bridged and frames that should be passed to the SRB module for handling.


Request Initialization Mode


Connection of two or more stations in a logically circular topology. Information is passed sequentially between active stations. Token Ring, FDDI, and CDDI are based on this topology.

ring group

Collection of Token Ring interfaces on one or more routers that is part of a one-bridge Token Ring network.

ring latency

Time required for a signal to propagate once around a ring in a Token Ring or IEEE 802.5 network.

ring monitor

Centralized management tool for Token Ring networks based on the IEEE 802.5 specification. See also active monitor and standby monitor.

ring topology

Network topology that consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop. Each station on the network connects to the network at a repeater. While logically a ring, ring topologies are most often organized in a closed-loop star. Compare with bus topology, star topology, and tree topology.


Routing Information Protocol. IGP supplied with UNIX BSD systems. The most common IGP in the Internet. RIP uses hop count as a routing metric. See also hop count, IGP, and OSPF. See also Enhanced IGRP and IGRP (Interior Gateway Routing Protocol) in the "Cisco Systems Terms and Acronyms" section.


Réseaux IP Européennes. Group formed to coordinate and promote TCP/IP-based networks in Europe.


reduced instruction set computing

RJ connector

registered jack connector. Standard connectors originally used to connect telephone lines. RJ connectors are now used for telephone connections and for 10BaseT and other types of network connections. RJ-11, RJ-12, and RJ-45 are popular types of RJ connectors.


remote job entry. Application that is batch-oriented, as opposed to interactive. In RJE environments, jobs are submitted to a computing facility, and output is received later.


remote login. Terminal emulation program, similar to Telnet, offered in most UNIX implementations.


Redundant Link Manager.


resource management. Management of critical resources in an ATM network. Two critical resources are buffer space and trunk bandwidth. Provisioning can be used to allocate network resources in order to separate traffic flows according to service characteristics.


remote monitoring. MIB agent specification described in RFC 1271 that defines functions for the remote monitoring of networked devices. The RMON specification provides numerous monitoring, problem detection, and reporting capabilities.


routing over large clouds. Working group in IETF created to analyze and propose solutions to problems that arise when performing IP routing over large, shared media networks such as ATM, Frame Relay, SMDS, and X.25.


read-only memory. Nonvolatile memory that can be read, but not written, by the microprocessor.

root account

Privileged account on UNIX systems used exclusively by network or system administrators.

root bridge

Exchanges topology information with designated bridges in a spanning-tree implementation in order to notify all other bridges in the network when topology changes are required. This prevents loops and provides a measure of defense against link failure.


Remote Operations Service Element. OSI RPC mechanism used by various OSI network application protocols.

round-trip time

See RTT.


Path through an internetwork.

Route Processor

See RP in the "Cisco Systems Terms and Acronyms" section.

routed protocol

Protocol that can be routed by a router. A router must be able to interpret the logical internetwork as specified by that routed protocol. Examples of routed protocols include AppleTalk, DECnet, and IP.

route extension

In SNA, a path from the destination subarea node through peripheral equipment to a NAU.

route map

Method of controlling the redistribution of routes between routing domains.

route summarization

Consolidation of advertised addresses in OSPF and IS-IS. In OSPF, this causes a single summary route to be advertised to other areas by an area border router.


Network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information. Occasionally called a gateway (although this definition of gateway is becoming increasingly outdated). Compare with gateway. See also relay.

route redistribution

See redistribution.

Route/Switch Processor

See RSP in the "Cisco Systems Terms and Acronyms" section.


Process of finding a path to a destination host. Routing is very complex in large networks because of the many potential intermediate destinations a packet might traverse before reaching its destination host.

routing domain

Group of end systems and intermediate systems operating under the same set of administrative rules. Within each routing domain is one or more areas, each uniquely identified by an area address.

Routing Information Field

See RIF.

Routing Information Identifier

See RII.

Routing Information Protocol

See RIP.

routing metric

Method by which a routing algorithm determines that one route is better than another. This information is stored in routing tables. Metrics include bandwidth, communication cost, delay, hop count, load, MTU, path cost, and reliability. Sometimes referred to simply as a metric. See also cost.

routing over large clouds


routing protocol

Protocol that accomplishes routing through the implementation of a specific routing algorithm. Examples of routing protocols include IGRP, OSPF, and RIP.

routing table

Table stored in a router or some other internetworking device that keeps track of routes to particular network destinations and, in some cases, metrics associated with those routes.

Routing Table Maintenance Protocol


Routing Table Protocol

See RTP.

routing update

Message sent from a router to indicate network reachability and associated cost information. Routing updates are typically sent at regular intervals and after a change in network topology. Compare with flash update.


See RP (Route Processor) in the "Cisco Systems Terms and Acronyms" section.


remote-procedure call. Technological foundation of client-server computing. RPCs are procedure calls that are built or specified by clients and executed on servers, with the results returned over the network to the clients. See also client/server computing.


Reverse Path Forwarding. Multicasting technique in which a multicast datagram is forwarded out of all but the receiving interface if the receiving interface is the one used to forward unicast datagrams to the source of the multicast datagram.


relative rate. In ATM, one of the congestion feedback modes provided by ABR service. In RR mode, switches set a bit in forward and backward RM cells to indicate congestion. See also ABR and RLM.


Popular physical layer interface. Now known as EIA/TIA-232. See EIA/TIA-232.


Balanced electrical implementation of EIA/TIA-449 for high-speed data transmission. Now referred to collectively with RS-423 as EIA-530. See also EIA-530 and RS-423.


Unbalanced electrical implementation of EIA/TIA-449 for EIA/TIA-232 compatibility. Now referred to collectively with RS-422 as EIA-530. See also EIA-530 and RS-422.


Popular physical layer interface. Now known as EIA/TIA-449. See EIA/TIA-449.


Acronym stands for Rivest, Shamir, and Adelman, the inventors of the technique. Public-key cryptographic system which may be used for encryption and authentication.


remote shell protocol. Protocol that allows a user to execute commands on a remote system without having to log in to the system. For example, rsh can be used to remotely examine the status of a number of access servers without connecting to each communication server, executing the command, and then disconnecting from the communication server.


Route Switch Module


See RSP (Route/Switch Processor) in the "Cisco Systems Terms and Acronyms" section.


remote source-route bridging. SRB over WAN links. See also SRB.


See RSUP (Reliable SAP Update Protocol) in the "Cisco Systems Terms and Acronyms" section.


Resource Reservation Protocol. Protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so forth) of the packet streams they want to receive. RSVP depends on IPv6. Also known as Resource Reservation Setup Protocol. See also IPv6.


RTP Control Protocol. Protocol that monitors the QOS of an IPv6 RTP connection and conveys information about the on-going session. See also RTP (Real-Time Transport Protocol).


read the fantastic manual. Acronym often used when someone asks a simple or common question.


Routing Table Maintenance Protocol. Apple Computer's proprietary routing protocol. RTMP establishes and maintains the routing information that is required to route datagrams from any source socket to any destination socket in an AppleTalk network. Using RTMP, routers dynamically maintain routing tables to reflect changes in topology. RTMP was derived from RIP. See also RIP (Routing Table Protocol).


1. Routing Table Protocol. VINES routing protocol based on RIP. Distributes network topology information and aids VINES servers in finding neighboring clients, servers, and routers. Uses delay as a routing metric. See also SRTP.

2. Rapid Transport Protocol. Provides pacing and error recovery for APPN data as it crosses the APPN network. With RTP, error recovery and flow control are done end-to-end rather than at every node. RTP prevents congestion rather than reacts to it.

3. Real-Time Transport Protocol. One of the IPv6 protocols. RTP is designed to provide end-to-end network transport functions for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. RTP provides services such as payload type identification, sequence numbering, timestamping, and delivery monitoring to real-time applications.

RTP Control Protocol



Request To Send. EIA/TIA-232 control signal that requests a data transmission on a communications line.


read the source code.


Real Time Streaming Protocol. Enables the controlled delivery of real-time data, such as audio and video. Sources of data can include both live data feeds, such live audio and video, and stored content, such as pre-recorded events. RTSP is designed to work with established protocols, such as RTP and HTTP.


round-trip time. Time required for a network communication to travel from the source to the destination and back. RTT includes the time required for the destination to process the message from the source and generate a reply. RTT is used by some routing algorithms to aid in calculating optimal routes.


request/response unit. Request and response messages exchanged between NAUs in an SNA network.


Reliable User Data Protocol

run-time memory

Memory accessed while a program runs.


required visual inspection.

Posted: Tue Sep 21 15:22:43 PDT 1999
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