Glossary- R
A Data Communication Historical Series
By Bob Pollard

HOME                        INDEX


Registration Authority: Optional PKI entity that does not sign either digital certificates or CRL(s), but has responsibility for recording or verifying some or all of the information needed by a CA to issue certificates and CRL(s), and also perform other certificate management functions.


Research on Advanced Communications in Europe: Project sponsored by the European Community (EC) for the development of broadband networking capabilities.


The process of acquiring the correct timing offset so the transmissions of a cable MODEM is aligned with the correct mini-slot boundary.


A frame on which equipment is mounted


A term used to describe devices designed to fit in a data cabinet or on a rack, sometimes in a ‘modular’ fashion.


Generally refers to wireless communications with frequencies below 300 GHz.


An electronic process that identifies each individual wireless handset by examining its unique radio transmission characteristics: Fingerprinting is used to reduce fraud since the illegal phone can not duplicate the legal phone's radio-frequency fingerprint.


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


Rate Adaptive Digital Subscriber Line: A version of ADSL where a MODEM tests the line at start up and adjusts the operating speed to the highest speed the line can handle.


Redundant Array of Independent Disks: Data is stored on multiple magnetic or optical disk drives to increase output performance and storage capacities and to provide varying degrees of redundancy and fault tolerance. Instead of storing valuable data on a single hard disk that could fail at any time, RAID makes sure a backup copy of all information always exists by spreading data among multiple hard disks.


Different RAID (Redundant Array of Independent Disks) levels offer trade offs among speed, reliability, and cost.

·         Level 0: is disk striping only for better performance. Its data transfer and I/O rates are very high, but it provides no safeguards against data failure.

·         Level 1: uses disk mirroring. All data is duplicated on two drives, offering the highest data reliability. Its data transfer rate is higher than a single disk for read and similar for write. Its I/O rate is twice that of a single disk for read but similar for write.

·         Level 1/0:  is a combination of Levels 1 and 2, mirroring and striping. It offers the same data reliability as RAID 1. Its data-transfer and I/O rates are very high, but slower than RAID 0 for writes

·         Level 3: stripes data across three or more drives. All drives operate in parallel to achieve the highest data transfer rate. Parity bits are stored on separate, dedicated drives. Its I/O rate is similar to a single disk.

·         Level 5: is the most widely used. Data is striped across three or more drives for high performance. The parity bits from two drives are stored on a third drive. Its data reliability is similar to RAID 3. Its data transfer and I/O rates are very high for read, but slower than a single disk for write.

RAID-5 volume: A fault-tolerant volume with data and parity striped intermittently across three or more physical disks. Parity is a calculated value that is used to reconstruct data after a failure. If a portion of a physical disk fails, Windows recreates the data that was on the failed portion from the remaining data and parity. A user can create RAID-5 volumes only on dynamic disks, and a user cannot mirror or extend RAID-5 volumes.


Random Access Memory: Usually the main memory system within the mainframe (computer) used for processing. Normally, without battery backup, stored information will be lost if power fails.


Congestion avoidance algorithm in which a small percentage of packets are dropped when congestion is detected and before the queue in question overflows completely


Process of acquiring the correct timing offset so the cable access router transmission is aligned with the correct mini-slot boundary.


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


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


1) Registration, Admission, and Status Protocol: Protocol that is used between endpoints and the gatekeeper to perform management functions. RAS signaling function performs registration, admissions, bandwidth changes, status, and disengage procedures between the VoIP gateway and the gatekeeper.

2) Remote Access Server


Fonts that are stored as bitmaps: Raster fonts are designed with a specific size and resolution for a specific printer and cannot be scaled or rotated. If a printer does not support raster fonts, it will not print them. The five raster fonts are Courier, MS Sans Serif, MS Serif, Small and Symbol. Raster fonts are also called bit-mapped fonts.


ADSL allows the MODEM to adjust the speed of the connection depending on the length and quality of the line. See RADSL


A defined geographic point used by telephone companies for distance measurements for inter- LATA mileage rates


Traffic Policing: Process used to measure the actual traffic flow across a given connection and compare it to the total admissible traffic flow for that connection. Traffic outside of the agreed upon flow can be tagged (CLP bit set to 1) and discarded en route if congestion develops. Traffic policing is used in ATM, Frame Relay, and other types of networks. Also known as admission control, permit processing, rate enforcement, and UPC


In ATM, a value associated with one or more virtual circuits that define 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.


MICA technologies interface mode in which no framing takes place. The other interface modes are PPP and SLIP. In raw mode, data is forwarded immediately without interpretation of individual characters.


Role-Based Access Control: Form of identity-based access control where the system entities that are identified and controlled are functional positions in an organization or process.


Regional Bell Holding Company: One of seven regional telephone companies formed by the breakup of AT&T. RBHC(s) is different from RBOC(s) because RBHC(s) cross state boundaries.


Regional Bell Operating Company: Refers to any of the seven U. S. Telephone companies that resulted from the break up of AT&T


Remote Batch Terminal: A remote input/output terminal designed to operate in a RJE location for transmitting and receiving data in batch processing form.


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.


Router or other device that acts as a server for RCP


Receive: Direction of signal moving from the high-speed receiver to the low- to medium-speed interface.


1) Received Data: RS-232 data signal received by a DTE device from a DCE device on pin 3

2) Request Disconnect


Resource Definition Framework: A set of rules (language) for creating descriptions of information, especially information available on the World Wide Web. RDF could be used to describe a collection of books, or artists, or a collection of web pages. RDF is also used in XPFE (Cross Platform Front End) applications to define the relationships between different elements, for example RDF could be used to define the relationship between the data in a database and the way that data is displayed to a user.


Remote Defect Indication:

1) Indication that a failure has occurred at the far end of the network. Unlike FERF (Far-End Remote Failure), the RDI alarm indication does not identify the specific circuit in a failed condition.

2) 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.

REACT 2000:

Hekimian's Operations Support System (OSS) for provisioning, monitoring, testing, and administering telecommunications networks.

 REACT 2001:

Hekimian's Operations Support System (OSS) that incorporates REACT 2000 capabilities while adding a Graphical User Interface (GUI), the ability to process across multiple computing platforms, a database with relational abilities, and improved communications with other OSS installations.


A frequency sensitive data communications line impairment: Causes phase shifting and power loss.


Process of re-enabling network access and privileges for a subscriber device and / or reclaiming device attributes for other subscriber devices.


Data can be retrieved (read) but not altered (written).


Rapid transmission and processing of event-oriented data and transactions:

1)A real-time system responds immediately at the time a transaction occurs, unlike a batch processing system which would produce journals, reports, and other outputs according to prescheduled batch processing cycles.

2) Real-time systems in which there is rapid and frequent interaction between human and machine are sometimes said to operate in a ‘conversational’ mode.

3) Inquiry – Response communications activity.


Refers to immediate action on information received, which will be processed, routed and transmitted quickly, along with other separate concurrent information being processed.


An anti-virus software application that operates as a background task, allowing the computer to continue working at normal speed


A testing method designed to ensure that data reaching a real-time computer or being transmitted from it is within a specified range. This process, also known as a limit check is a means of protecting a system from data transmission errors.


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.


To restart a computer by reloading the operating system: This can be done by performing either a cold boot, such as turning the computer off and then back on, or a warm boot, such as turning the computer off by typically pressing CTRL + ALT + DEL, clicking Shut Down, and then clicking Restart.


The process or device assigned to receive messages, a frame, token, data or a control sequence in a data communications network, usually, but not always, at a DTE device.


RS-449 signal (Pin 20) return for receiver circuit reference.


The designated data receiving circuit (pin 3) in an RS-232C cable for DTE (Data Terminal Equipment); RS-449: Pins 6A and 24B.


A device capable of receiving data, but unable to transmit, such as a printer

RECEIVE TIMING (Transmitter Signal Timing):

RS-449 (Pin 8A & 26B): Transmission timing signals (clock) originating at the DCE (Data Communication Equipment) end; used by the DTE (Data Terminal Equipment) for receiving data.


See Carrier Detect.


A group of related facts or fields of information treated as a unit.


A data communications control character.


The procedure or process performed to restore a computer system to a predetermined level of operation or availability after a failure.


A person who is issued a public key certificate for the purpose of recovering user data that is encrypted with Encrypting File System (EFS)


A command line interface that provides a limited set of administrative commands, which are useful for repairing a computer


An area in which Windows stores deleted files: a user can retrieve files that were deleted in error, or can empty the Recycle Bin to create more disk space.


An out-of-frame alarm condition, for two to three seconds, in T1 for an incoming DS1 signal. Synonym: loss of signal alarm


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


1) The action used by some viruses to point a command to a different location. Often this different location is the address of the virus and not the original file or application.

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


A server that accepts a SIP request, maps the address into zero or more new addresses, and returns these addresses to the client. It does not initiate its own SIP request nor does it accept calls.


1) A station on a LAN: Receives information from a network server and redirects the information to the local user.

2) 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; satisfying the request.


Route Redistribution: Allowing routing information discovered through one routing protocol to be distributed in the update messages of another routing protocol.


1) A repetition of information or the insertion of information, which is not new, and therefore redundant: Example: the use of check bits and check characters for error detection is a form of redundancy, hence the terms: cyclic redundancy, longitudinal redundancy and vertical redundancy check. Could also be the duplication of equipment for fallback purposes in order to protect for component failures.

2) 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 the failed media.

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


A hardware or software validity check based on the systematic insertion of bits or characters. See Redundancy


Backup arrays, drives, disks or power supplies that duplicate functions performed elsewhere.


A code that uses more signal units than needed to represent transmitted information.


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


·         Code: A forward-error correction technique used for satellite transmission and CD recordings.

·         Encoder: Device that takes a block of digital data and adds extra ‘redundant’ bits: When errors occur during transmission or storage, the Reed-Solomon decoder processes each block and attempts to correct errors and recover the original data. The number and type of errors that can be corrected depends on the characteristics of the Reed-Solomon code. Reed-Solomon codes are used in storage devices, barcodes, wireless or mobile communications, microwave links, satellite communications, digital television/DVB, high-speed MODEMS, etc.


A noise level equivalent to 1 picowatt of power at 1,000 Hz (1 picowatt = -90 dBm)


Used in carrier systems to allow the adjustment of carrier transmission signals.


Type of replay attack in which transmitted data is sent back to its originator


Reflexive access lists contain condition statements (entries) that define criteria for permitting IP packets. These entries are evaluated in order, and when a match occurs, no more entries are evaluated.


A meta tag that will let a person either periodically refresh the current page or switch to another page.


The rate at which a CRT image is renewed for a consistent appearance: Approx. 60 times per second.


Regeneration Stations: Points on a fiber-optic network spaced about 30 miles apart, where optical signals are regenerated (amplified and restored).


A device that amplifies, reshapes, and re-times distorted incoming signals then retransmits them on an outgoing circuit.


Unix term for ‘Regular Expression’: A series of characters used in a search. The characters &, $, ^, \, and square brackets are given special meanings in regular expressions.


A class 1 central office connecting portions of the telephone system together, with each pair of regional centers having a direct circuit group running from one center to the other.


Server that accepts Register requests


Administrative act or process where an entity's name and other attributes are established for the first time at a CA, prior to the CA issuing a digital certificate that has the entity's name as the subject.


A database repository for information about a computer's configuration: The registry contains information that Windows continually references during operation, such as:

·         Profiles for each user

·         The programs installed on the computer and the types of documents each can create.

·         Property settings for folders and program icons

·         What hardware exists on the system

·         Which ports are active

The registry is organized hierarchically as a tree and is made up of keys and their sub-keys, hives, and value entries.


To deliberately change the classification level of information in an authorized manner


Change the value of a cryptographic key that is being used in an application within a cryptographic system.


The part of a Security ID (SID) that uniquely identifies an account or group within a domain


1) Term used to describe a communications switching center or an intermediate station (terminal).

2) An electronically operated switch with one or more contacts.

3) A device in which low power flow (current) can control a larger power flow in a secondary circuit through the use of opening and closing contacts. Usually contains an electromagnet and armature.

4) Open System Interconnection (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.


From a quantitative standpoint, reliability is the probability that the system or data communications network will perform its intended function over the stated duration of time in the specified environment for its usage. From a qualitative sense, reliability is closely connected with maintainability, availability, and system security from unauthorized access.


Bandwidth-saving protocol developed by Cisco for propagating services information. RSUP allows routers to reliably send standard Novell SAP packets only when the routers detect a change in advertised services. RSUP can transport network information either in conjunction with or independently of the Enhanced IGRP routing function for IPX.


The event of a computer and / or router rebooting, or the command that causes the reboot action


An arrangement where distant terminals, via a communications channel, have access to a central computer for data processing


An alarm received at the transmit end of the circuit to indicate that a failure has occurred at the receive station.


Yellow Alarm


A diagnostic test that loops the analog side of the remote MODEM back to a distant device for isolation of line and equipment faults.


Set of interfaces that allow Cisco IOS software to control the operation of a remote ATM switch through a control protocol, such as a VSI.


A method of submitting jobs to a computer through a remote terminal


A high-throughput device for connecting remote Local area Networks (LAN) to a Wide area Network (WAN)


A diagnostic test: Creates a loop at the channel (line) side of the remote DTE or multiplexer.


A diagnostic test: Creates a loop at the composite or output (line) side of the remote DTE or multiplexer.


A diagnostic test: Creates a loop at the remote DTE (DC) side.


The submission of processing jobs to a central computer from a distant location


A service offered by Berkeley 4BSD Unix systems that allow users of one machine to connect to other Unix systems across an Internet and interact as if their terminals connected to the machines directly.


RS-449 signal (Pin 14) – A signal from the DTE (Data Terminal Equipment) to the DCE (Data Communication Equipment) that causes a loop-back on the analog signal side of the line.


Refers to the use of a common computer system for processing data transmitted from other locations; the assignment of various processing jobs to distant locations with primary control at the central processor. This action would result in a distribution of the workload.


Starting a computer and loading the software operating system into computer memory from a server on the network.


A device that is available through the network, but is not connected to the local node.


A device attached by a communication line or telephone link to a controlling unit.


End system or router that is attached to a remote access network and is either the initiator or the recipient of a call.


A service that provides removable media, such as tapes and discs, and storage devices (libraries): Removable Storage allows applications to access and share the same media resources.


The action by which a user or program assigns a new name to a file. Viruses may rename program files and take the name of the valid file so running the program inadvertently runs the virus.

Anti-virus programs may rename infected files making them unusable until they are manually cleaned or deleted.


In color management, the approach used to map the colors specified in an image file to the color gamut of a users monitor or printer. The color gamut is the range of color that a device can produce.


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

Refers to token-passing networks, where a station receives a frame or token from an upstream station, repeats it, and places it onto the ring for its downstream neighbor. A repeating station can examine, copy, or modify control bits in the frame. In some types of networks, the frame or token is re-timed when repeated.


A delay in the amount of time that elapses before a character begins repeating when a key is held down on the keyboard.


A device, unit or combination of apparatus that receives communication signals and delivers (re-transmits) corresponding signals which are amplified and/or reshaped and any distortion is removed.


A device that automatically punches a paper tape based on the received signals (characters). A Perforator would punch a tape based on a keyboard input at a terminal, the tape would then be transmitted via a paper tape reader; the receiving Re-perforator would punch a tape based on the received signals from the line that would be used for processing or switching.


Attack in which a valid data transmission is maliciously or fraudulently repeated, either by the originator or by an adversary who intercepts the data and retransmits it, possibly as part of a masquerade attack.


A folder within a replica set. See Replica set and Replication


One or more shared folders that participates in replication (duplication)


1) Process of keeping a copy of data through shadowing or caching

2) The process of copying data from a data store or file system to multiple computers to synchronize the data. Active Directory provides multi-master replication of the directory between domain controllers within a given domain. The replicas of the directory on each domain controller are writable. This allows updates to be applied to any replica of a given domain. The replication service automatically copies the changes from a given replica to all other replicas.

3) The process in which a virus makes copies of itself in order to carry out subsequent infections: Replication is one of major criteria separating viruses from other computer programs.


Automatic or manually initiated data or communications activity reports: A pre-set criteria or defined action would trigger a pre-formatted report, with the report information varying based on the processed information being monitored.


System for storing and distributing digital certificates and related information to certificate users, including CRL(s), CPS(s), and certificate policies


Denial by a system entity that was involved in an association of having participated in the relationship, especially an association that transfers information


An official document of the Internet Engineering Task Force (IETF) that specifies the details for protocols included in the TCP/IP (Transmission Control Protocol/Internet Protocol) family.

REQUEST TO SEND (RTS):A basic data set interchange lead (defined in an EIA Standard). Example: The computer tells the MODEM it wants to send information by raising a signal (voltage) on the RTS lead; RS232, Pin 4 and RS449, Pins 7 and 25.


1) A specific IP (Internet Protocol) address within an address group permanently reserved for leased use to a specific DHCP (Dynamic Host Configuration Protocol) client. Client reservations are made in the DHCP database using DHCP Manager and based on a unique client device identifier for each reserved entry.

2) In Admission Control Service, an allocation of network resources, contained in a Resource Reservation Protocol (RSVP) reservation request; administered by the Admission Control Service.


Block maintained by RSVP to store a reservation


Storage batteries that back-up the primary power source in a computer, telephone system or other devices; Un-interruptible power supply


To restart a computer without turning it off (no power down)


A resident extension is a memory-resident portion of a program that remains active after the program ends. It essentially becomes an extension to the operating system. Many viruses install themselves as resident extensions.


A resident virus loads into memory and remains inactive until a trigger event. When the event occurs the virus activates, either infecting a file or disk, or causing other consequences. All boot viruses are resident viruses and so are the most common file viruses.


Customer premises equipment running XGCP that has connections to the VoIP network and connections to user telephony equipment.


The ratio of error bits to the total number of bits sent (transmitted)


Risk that remains after countermeasures have been applied


DNS (Domain Name System) client programs used to look up DNS name information. A Resolver can be either a small stub, a limited set of programming routines that provide basic query functions, or larger programs that provide additional lookup DNS client functions, such as caching.


1) Generally, any part of a computer system or network: Such as a disk drive, printer, or memory that can be allotted to a running program or a process.

2) For Device Manager: any of four system components that control how the devices on a computer work. These four system resources are Interrupt Request (IRQ) lines, Direct Memory Access (DMA) channels, Input/Output (I/O) ports, and memory addresses.

3) For server clusters: a physical or logical entity that is capable of being managed by a cluster, brought online and taken offline, and moved between nodes. A resource can be owned only by a single node at any point in time.


A term used in a LAN environment to identify a group of computer or computer ports offering similar facilities, such as an application program, and identified by a symbolic name.


A Dynamic Link Library (DLL) containing a compliment of the resource Application Programming Interface (API) for a specific type of resource. The Resource DLL is loaded into the address space of its Resource Monitor.


A Windows NT 4.0 domain that is used for a hosting file, print, and other application services


In Windows remote access, strings expected from the device, which can contain macros


In data communications the term would refer to the amount of time that elapsed between the generation of an inquiry at a terminal and the receipt of a response at the same terminal, ‘inquiry-response’.


REpresentational State Transfer: A loosely defined specification for HTTP-based services where all of the information required for processing a request is present in the initial request and each request receives only a single response, and the response is in a machine-readable form.
  An example could be a service that accepts HTTP requests for a search and returns the result as an XML document.


To return a failed service, system or device to satisfactory operation through repair, reassignment, rerouting, substitution of parts, etc.


A representation (status) of the present state of a user’s computer: Restore point is created by System Restore at specific intervals, and when System Restore detects the beginning of a change in the computer. Also, restore point can be created manually at any time.


A limited digital communications channel operating at a reduced speed (I.E. 56 Kbps instead of 64 Kbps) due to channel restrictions.


A token denoting a special mode of asynchronous bandwidth allocation: The bandwidth available for the asynchronous class of service is dedicated to single dialogues between specific requesters.


The restoration of the synchronous mode of operation following an error condition: Or in framing a signal correction performed because two frame synchronization errors were detected. As a result, the signal is re-framed and the pattern is re-synchronized.


A component used in fiber optic transmission that permits the light signal on the input fiber to be retransmitted on multiple output fibers.

RETRY:Re transmitting a block, field, or other unit of data a predefined number of times


The opposite of NRZ (Non-Return to Zero), the voltage levels return to zero after each encoded bit.


A telecommunications path through a dual purpose MODEM used for transmitting supervisory or error control signals. The reverse data flow, with a lower bandwidth, is opposite to the information data transfer. The Reverse Channel would be used for error control, diagnostics, circuit assurance and circuit breaking, or in some cases slow speed data communications.


A receiver generated control character sent to request termination of an in-progress transmission.


A telephone directory service where a given phone number can be used to cross reference a name.


Radio Frequency: Generic term referring to frequencies that correspond to radio transmissions; wireless communications with frequencies below 300 GHz. Cable TV and broadband networks use RF technology.

RF (Radio Frequency) NOISE:

Undesired radio signals that alter a radio communications signal causing extraneous sounds during transmission and/or reception.


Request for Comments: Internet: The process of creating an Internet standard and the name of the standard. New standards are proposed and published on the Internet, as a Request for Comments. The proposal is reviewed by the Internet Engineering Task Force, a consensus building body that facilitates discussion, and eventually a new standard is established, and the reference number/name for the standard retains the acronym RFC, i.e. the official standard for E-mail message formats is RFC 822.


Radio Frequency Interference: An undesired radio signal that interferes with a radio communication signal causing extraneous noise and/or signal dropouts.


Request For Proposal.


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


Represents the colors Red, Green, and Blue: Used in color coding web pages, such as GIF files; 64K color values can be represented by a byte (8 bits) each for red, green, and blue


Regional Holding Company


Routing Information Field: A 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.


Position the mouse pointer over an object; then press and release the secondary (right) mouse button. Right-clicking opens a shortcut menu that contains useful commands, based on the pointer position.


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


Refers to the design topology of a local area network in which the wiring is sequentially connected from one workstation to another, forming a ring. Data is passed from each workstation around the ring in one direction. Each workstation examines or copies and repeats the data, which finally returns to the originating station.


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


RS232-C (pin 22): Designation and sense (signal) circuit used by the terminal or computer to detect the presence of ringing voltage on the communication circuit, identifying an incoming call; RS-449 signal from the DCE (Data Communication Equipment) to the DTE (Data Terminal Equipment).


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


The part of a Station Management (SMT) function that ensures the integrity of unique addresses on the Fiber-Distributed Data Interface (FDDI) ring.


Centralized management tool for Token Ring networks based on the IEEE 802.5 specification


A network topology with decentralized control: Messages are passed around the ring from node to node until they reach their destination or address; most use the token-passing access method.


A command on a token ring or Fiber-Distributed data Interface (FDDI) networks that resets the Network Interface Card (NIC) and creates a new token.


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. Although logically a ring, ring topologies most often are organized in a closed-loop star.


20 Hz AC at a voltage of 75 to 105 supplied by the central office to ring the subscriber's telephone bell.


Audible Ringing Tone


A circuit or method of signaling where the incoming signal utilizes alternating current over the circuit


A sound from your phone used to signal an incoming call or message. On most new phones additional sounds can be downloaded from the wireless system or by data cable. Many sound variations are possible and the most popular sounds are music.


See Routing Information Protocol


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


Reduced Instruction Set Computing


Process that systematically identifies valuable system resources and threats to those resources; quantifies loss exposures (loss potential) based on estimated frequencies and costs of occurrence, and optionally recommends how to allocate resources to countermeasures so as to minimize total exposure.


Process of identifying, controlling, and eliminating or minimizing uncertain events that might affect system resources


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.


The modular jack and plug interface used with a standard, single line telephone.


The modular jack and plug interface used with a standard, single line telephone when used for alternate voice and data. An RJ16X modular jack would be used to connect the MODEM.


The designation for the eight-pin modular connector in the 10BaseT standard for Unshielded Twisted Pair (UTP) connections: This standard refers to workstations or smart wiring hubs. The actual connector is described in International Standards Organization (ISO) standard 8877.


A modular jack for data transmission purposes; programmed by inserting a proper value resistor, used with a programmable type MODEM.


Redundant Link Manager


Remote Login: Terminal emulation program, similar to Telnet, offered in most UNIX implementations. See Remote Login


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.


See Ring Management

RO or R/O:

See Receive Only

If the SID (System Identification Code) on the cell phone control channel does not match the SID programmed into the cell phone, the cell phone knows it is roaming. The MTSO (Mobile Telephone Switching Office) of the cell where the phone in question is roaming contacts the MTSO assigned to the phones home system, which then checks its database to confirm that the SID of the phone detected is valid. The home system verifies the phone to the local MTSO, which then tracks the phone as it moves through its cells. All of this happens within seconds.


Dial service for cable subscribers that require access away from their cable MODEM


Able to function or continue to function in a variety of unanticipated situations


A term the media use to denote any program intended to damage programs or data, or to breach a system's security. It includes Trojan horse programs, logic bombs, viruses, etc.


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: A semiconductor media into which code or data is permanently installed by a manufacturing process. ROM contains instructions or data that can be read but not modified. The stored information normally cannot be re-written or altered.


The highest or uppermost level in the hierarchy of an organized set of information: The root is the point from which further subsets are branched in a logical sequence.


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


The Certification Authority (CA) at the top of a certification hierarchy; also called the root certification authority. The root CA has a self-signed certificate


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


Ultimate CA, which signs the certificates of the subordinate CA(s): The root CA has a self-signed certificate that contains its own public key.


A self-signed certification authority certificate: It is called a root certificate because it is the certificate for the root authority. The root authority must sign its own certificate because by definition there is no higher certifying authority in the certification hierarchy.


Public key for which the matching private key is held by a root


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


A group (several) contiguous lines that allow a connection to be made to the next free line in the group


An arrangement that allows incoming dialed calls to seek out an idle circuit in a prearranged multi-circuit group, or find the next open line to establish a through circuit.


Receive Only Teletype Re-perforator


A path through an inter-network, network or any end to end line connection.

  The action of directing of a message to the appropriate network, line or station (terminal) based on information contained in the message header.


A type of automatic route selection: Allows the caller (sender) to select the first-choice trunk group.


An 8-byte value that is concatenated with an IPv4 prefix to create a unique VPN IPv4 prefix


A condition where two or more private-line circuits are partially or entirely routed over two physically separate routes: Prevents a total loss of service if one cable (line) gets cut or damaged.


In SNA, a path from the destination sub-area node through peripheral equipment to an NAU


Refers to Least Cost Routing


Method of controlling the redistribution of routes between routing domains


Processor module in the Cisco 7000 series routers that contains the CPU, system software, and most of the memory components that are used in the router


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.


Processor module in the Cisco 7500 series routers that integrate the functions of the RP and the SP


The process in which a stub-bridged segment is terminated on a point-to-point routed interface. Specifically, the router is routing on an IEEE 802.3 or Ethernet header carried over a point-to-point protocol, such as PPP, RFC 1483 ATM, or RFC 1490 Frame Relay.


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


1) A packet switching computer system that routes data between networks using IP addressing: Routers also provide firewall security. Large Routers are the main backbone of the Internet.

2) 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. May be called a gateway


1) Scheduled preventative maintenance; 2) A computer data processing program the machine uses to perform repetitive tasks.


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.


The backup facilities or secondary path to a destination used in the event of link failure or component breakdown.


See routing Indicator


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.


A group of characters in the header of a message that identifies the final circuit or terminal to which the message should be delivered


The standard protocol used by network devices that use the transport layer of Transmission Control Protocol/Internet Protocol (TCP/IP) to exchange routing information.


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.


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


A data (address) matrix: Contain available routes and such parameters as user class of service and destination. A switching software table used in order to select a route for a designated address/call.

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.


Message sent from a router to indicate network reach-ability and associated cost information. Routing updates typically are sent at regular intervals, and after a change in network topology.


Route Processor: Processor module in the Cisco 7000 series routers that contains the CPU, system software, and most of the memory components that are used in the router.


Remote-Procedure Call: Technological foundation of client / server computing. RPC(s) are procedure calls that are built or specified by clients and are executed on servers, with the results returned over the network to the clients.


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


See Remote Program Load


Restore Path request: The RPR is a WaRP request sent using a Restore Path packet that is used to establish a virtual path between two nodes. The request is sent by a source node, or a proxy source node, to establish an intra-zone path for a VWP. The packet usually is sent during failure recovery procedures but also can be used for provisioning new VWP(s). The node that sends the request is called the originating node. The node that terminates the request is called the target node.


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.


Registration Rejection: RAS message sent as a registration rejection


Registration Request: RAS message sent as a registration request


FS, GS, RS, US - File Separator, Group Separator, Record Separator, and Unit Separator: Information separators used within data in an optional fashion. The hierarchical relationship will usually be FS is the most inclusive, then GS, then RS and US the least inclusive.


1) Rural Service Area: Areas not included in a MSA (Metropolitan Statistical Area) are divided into RSA(s). Generally these are the rural areas of the US. The FCC (Federal Communications Commission) uses the RSA(s) to license cellular carriers in areas not included in the MSA(s). There are 428 RSAs in the US.

2) Rivest, Shamir, and Adelman: The inventors of the technique for a Public-key cryptographic system that can be used for encryption and authentication


Receiver Select Code: Used to select a designated terminal on a multi-point line.


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; rsh executes the command, and then disconnects from the communication server.


Re-Start In Progress: MGCP command used to indicate that a span, or collection of spans, has come into service, has gone out of service, or is about to go out of service.


Route Switch Module


Route/Switch Processor: Processor module in the Cisco 7500 series routers that integrates the functions of the RP and the SP


Remote Source-Route Bridging: SRB over WAN links.


‘Rich Site Summary’ or ‘RDF (Resource Definition Framework) Site Summary’ or ‘Real Simple Syndication’: A commonly used protocol for syndication and sharing of content, originally developed to facilitate the syndication of news articles, now widely used to share the contents of blogs. RSS is an XML (Extensible Markup Language) based summary of a web site, usually used for syndication and other kinds of content-sharing.

Reliable SAP Update Protocol: Bandwidth-saving protocol developed by Cisco for propagating services information. RSUP allow routers to reliably send standard Novell SAP packets only when the routers detect a change in advertised services. RSUP can transport network information either in conjunction with or independently of the Enhanced IGRP routing function for IPX.


A device, which allows Commodore 64 and 128 computers to use a common external MODEM designed for other platforms. Accommodates the RS-232 Standard


The Electronic Industries Association (EIA) standard for the communication interface between Data Communications Equipment (DCE) and Data Terminal Equipment (DTE): The 25-pin connector and signaling standard is presented on the following page.

RS 232-C signals and connector:

Pin 1 – Protective ground

Pin 2 – Transmitted Data (to MODEM)

Pin 3 – Received Data (to Terminal)

Pin 4 – Request to Send (to MODEM)

Pin 5 – Clear to Send (to Terminal)

Pin 6 – Data Set Ready (to Terminal)

Pin 7 – Signal ground (common return)

Pin 8 – Received Line Signal Detector (to Terminal)

Pin 9 – Reserved for MODEM testing

Pin 10- Reserved for MODEM testing

Pin 11- Unassigned

Pin 12- Sec. Receive Line Signal Detector (to Terminal)

Pin 13- Sec. Clear to Send (to Terminal)

Pin 14- Sec. Transmitted Data (to MODEM)

Pin 15- Transmit Timing (to Terminal)

Pin 16- Sec. Received Data (to Terminal)

Pin 17- Receive Timing (to Terminal)

Pin 18- Unassigned

Pin 19- Sec. Request to Send (to MODEM)

Pin 20- Data Terminal Ready (to MODEM)

Pin 21- Signal Quality Detector (either way)

Pin 22- Ring Indicator (to Terminal)

Pin 23- Data Rate Detector (DTE/DCE) (either way)

Pin 24- Transmit Timing (to MODEM)

Pin 25- Unassigned


A designation for the Electronic Industries Association (EIA) standard for the defined electrical characteristics of balanced-voltage digital interface circuits: The definition and standard for RS 449 pins and connections.


A designation for the Electronic Industries Association (EIA) standard for the electrical characteristics of unbalanced-voltage digital interface circuits: Basis for RS 449 standards.


A designation for the Electronic Industries Association (EIA) standard that is compatible with RS-232C, but supports higher data rates at greater distances: The RS-449 interface uses a 37-pin connector and supports transmission data rates up to 2 Mbps at distances up to 200 feet. The 37-pin connector and signaling standards is presented in the next entry.


Pin 1 – Shield (Frame ground)

Pin 2 – Signaling rate Indicator (from DCE ‘Data Communication Equipment’)

Pin 3 – Not used

Pin 4 – Send Data (to DCE)

Pin 5 – Send Timing

Pin 6 – Receive Data (from DCE)

Pin 7 – Request to Send (to DCE)

Pin 8 – Receive Timing (from DCE)

Pin 9 – Clear to Send (from DCE)

Pin 10 – Local Loopback (to DCE)

Pin 11 – Data Mode (from DCE)

Pin 12 – Terminal Ready (to DCE)

Pin 13 – Receiver Ready (from DCE)

Pin 14 – Remote Loopback (to DCE)

Pin 15 – Incoming Call (from DCE)

Pin 16 – Signaling Rate Selector (to DCE)

Pin 17 – Terminal Timing to (DCE)

Pin 18 – Test Mode (from DCE)

Pin 19 – Signal Ground

Pin 20 – Receive Common

Pin 21 – Not used

Pin 22 – Send Data (to DCE)

Pin 23 – Send Timing (from DCE)

Pin 24 – Receive Data (from DCE)

Pin 25 – Request to Send (to DCE)

Pin 26 – Receive Timing (from DCE)

Pin 27 – Clear to Send (from DCE)

Pin 28 – Terminal in Service (to DCE)

Pin 29 – Data Mode (from DCE)

Pin 30 – Terminal Ready (to DCE)

Pin 31 – Receiver Ready (from DCE)

Pin 32 – Select Standby (to DCE)

Pin 33 – Signal Quality (from DCE)

Pin 34 – New Signal (from DCE)

Pin 35 – Terminal Timing (to DCE)

Pin 36 – Standby Indicator (to DCE)

Pin 37 – Send Common (to DCE)

RS-449 (secondary) signals and connector:

Pin 1 – Shield

Pin 2 – Secondary Receiver Ready

Pin 3 – Secondary Send Ready

Pin 4 – Secondary Receiver Data

Pin 5 – Signal Ground

Pin 6 – Receive Common

Pin 7 – Secondary Request to Send

Pin 8 – Secondary Clear to Send

Pin 9 – Send Common


Re-perforator-Transmitter (paper Tape)


RTP Control Protocol: Protocol that monitors the QoS of an IPv6 RTP connection and conveys information about the on-going session.


Routing Table Maintenance Protocol: Apple Computer's proprietary routing protocol: RTMP establishes and maintains the routing information that is required to route data-grams from any source socket to any destination socket in an AppleTalk network. Using RTMP, routers dynamically maintain routing tables to reflect changes in topology.


Rich Text Format File: RTF is an alternative format to the DOC file type supported by Microsoft Word.

RTF files are ASCII text files and include embedded formatting commands. RTF files do not contain macros and cannot be infected with a macro virus. This makes RTF files a good document format for communicating with others via e-mail. However, some macro viruses attempt to intercept the saving of a file as an RTF file and instead cause it to be saved as a DOC file with an RTF extension. Users can catch this trick by first reading the file in a simple text editor like Notepad. DOC files will be nearly unreadable, while RTF files will be readable. The normal file type has the extension RTF.


Read The Fantastic Manual: Acronym often used when someone asks a simple or common question.


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.

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: Commonly used with IP networks. 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 such services as payload type identification, sequence numbering, time-stamping, and delivery monitoring to real-time applications.


See Request to Send


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 as 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 to 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 NAU(s) in an SNA network.


Reliable User Data Protocol


Memory accessed while a program runs


1) Reverse Interrupt: A communications control character that is transmitted by a receiving terminal requesting a cancellation of the current transmission, so that it may send a higher priority message of its own.

2) Required Visual Inspection


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, etc) of the packet streams they want to receive. RSVP depends on IPv6. RSVP is also known as Resource Reservation Setup Protocol.