R

R interface - See Reference Point R.

R - 1. The symbol for Resistance. See resistance. 2. R interface or Reference Point R in ISDN. See Reference Point R.

R/C (Radio Control) - Radio Service. In the United States, a one-way, short distance, radio service for on/off operation of remote devices. An R/C unit is not authorized to communicate voice or data. R/C operates in the 72.0–73.0 MHz and 75.4–76.0 MHz bands. The Federal Communications Commission (FCC) regulates R/C, which is in the family of personal radio services. See also FCC and personal radio services.

R1022 ATM Technology Testbed (RATT) - The result of the 1987 RACE sponsored project 1022. See also RACE.

RA (Registration Authority) - In a public key infrastructure (PKI), an entity that verifies the certificate authority (CA) prior to the issuance of a digital certificate to the requesting party. See also CA, digital certificate, and PKI.

RA (Return Authorization) - Also known as RMA (Return Material Authorization) or RAN (Return Authorization Number). A reference number in the advance-replacement process. If you receive a shipment from a distributor or manufacturer and a part is defective, you call the distributor/manufacturer and they give you an RA or RMA number to place on the package when you send it back to them. They, in turn, send you a replacement immediately.

RACE (Research for Advanced Communications in Europe) - A consortium of European carriers, end users, and universities. In 1987, RACE sponsored project 1022 to demonstrate the feasibility of asynchronous transfer mode (ATM).The result of the RACE initiative was the R1022 ATM Technology Testbed (RATT). RACE project 2061, also known as EXPLOIT, is a more recent RACE project intended to prove the viability of integrated broadband communications (IBC) in the European Union (EU). The National Research and Education Network (NREN) was the first (1990) test-bed ATM network in the United States.Advanced Communications Technologies and Services (ACTS) was developed as the successor program to RACE, and continues that work on ATM networking and some 200 other projects. See also ATM.

Raceway - A trough designated for wiring. Raceways can be in ceilings, attached to walls, or built into floors.

Rack - Also called relay rack. The two standard dimensions of racks used in telephony and rack-mountable computer equipment are 19" and 22" wide. The height ranges from one to seven feet. Some racks can be attached to walls (wall mount). Most racks are rated as zone 4, which means that they are designed to withstand earthquakes to a certain degree.

Radar (Radio Detection and Ranging) - Radar is a means of detecting objects within the vicinity of a radio signal. Different types of objects can be detected, depending on the frequency of radio used. Radar works by sending a pulse from a transmitter: the pulse travels outward, bounces off objects, and is returned to a receiver. The time difference between the pulses departure and arrival determines the distance of the object. Any Doppler effect on the pulse determines the speed of the object toward (or away from) the transmitter.

Radar Detector - Radar detectors are famous for their use in speed-limit enforcement in the United States. Radar detectors use radar technology to measure the Doppler effect of radio signals that are sent from a transmitter, bounced off of a moving object, then returned at a different frequency. The movement of the object compresses the radio signal as the two come into contact, thus increasing the frequency.

radian - From the Latin radius.A unit of plane angular measurement equivalent to the angle between two radii that enclose a section of a circle’s circumference (arc) equal in length to the length of a radius.There are 2π radians in a circle. See also frequency and radius.

radiant flux - The time rate of energy flow of radiant energy as measured in watts or joules per second. See also flux, joule, radiation, and watt.

radiation - 1. The act or process of the spreading out of energy in rays. 2.The emission, or outward flow, of energy in the form of electromagnetic waves, including radio waves and photons. See also electromagnetic, photon, and waveform.

radio access network (RAN) - See RAN.

Radio Act of 1927 - In the United States, the act that established the Federal Radio Commission to regulate all radio spectrum, except bands owned by federal government.The Communications Act of 1934 replaced the Federal Radio Commission with the Federal Communications Commission (FCC). See also band, Communications Act of 1934, FCC, and spectrum.

radio area network (RAN) - Synonymous with wireless radio area network (WRAN). See WRAN.

Radio Common Carrier (RCC) - A cellular/PCS service provider or paging company. A company that provides one-way (paging) or two-way (mobile phone) radio services to individuals, rather than communities. Broadcast TV or radio stations are not radio common carriers.

Radio Control (R/C) Radio Service - See R/C Radio Service.

Radio Frequency (RF) - Any electromagnetic frequency that is above the range of human hearing. Most licensed radio transmissions range from 500 kHz (500,000 Hz) to 300 GHz (300,000,000,000 Hz).

Radio Frequency Interference (RFI) - Also called EMI (Electromagnetic Interference). Interference caused by a radio signal or other magnetic field inducing itself onto a medium (twisted/nontwisted pair wire) or device (telephone or other electronics). The world we live in is full of radio waves that are emitted from electric appliances, such as blenders, automobile engines, transmitters, and even fluorescent lights. Even though we take preventative measures to avoid receiving these unwanted signals, they sometimes get into places they are not wanted. Electromagnetic interference is usually caused by one of two things. The first is when a wire connected to a device acts like an antenna and picks up the EMI, which is then passed on to the electronics inside the device and amplified. The second is when an electronic component inside a device acts like an antenna because of poor design, poor shielding, or the component is defective.

Radio Frequency Interference (RFI) - See RFI

radio guide (RG) - See RG.

radio line-of-sight (radio LOS) - See LOS.

Radio Modem - A type of data-transmission device that is used where leased telephone lines are of either poor quality, are unavailable, or are very expensive. They operate at frequencies that range from 400 Hz to 2.4 GHz. They have a point-to-point range of three to 30 miles, depending on the weather of the region, the operating frequency, and the design of the radio circuitry. These types of modems have a net throughput that ranges from 300 bps to more than 2 Mbps. More recently, this communications solution has evolved to terrestrial microwave radio, which also requires licensing to operate. For more info and an illustration, see Terrestrial Microwave.

Radio - The emission of electromagnetic radiation into the air, then picking it up with a receiver. Electromagnetic radiation occurs when a magnetic field changes at the rate of a carrier frequency. The magnetic field then traverses through the farthest reach of the magnetic field, which could be many miles. One determining factor in the distance that the signal will reach is the transmitting power. Broadcast radio has a typical output power of 15 to 100 kW (15,000 to 100,000 watts) and CB radios have an output power of 4 w. What makes the radio signal carry a voice or music is called modulation. Modulation is the act of varying a carrier signal in a way that can be sensed or “detected” by a radio receiver. Those variations are then amplified and run through a speaker so that people can hear them.

radiophone - See photophone.

RADIUS (Remote Authentication Dial-In User Service) - An Internet protocol used for authentication, authorization, and accounting of end users seeking to gain access to internal computer resources, generally through a network access server (NAS) or, for remote users, by dialing into a remote access server (RAS). Originally developed by Livingston Enterprises, RADIUS was later described by the IETF in RFCs 2058 and 2059 and is currently described in RFCs 2865 and 2866. See also authentication, authorization, IETF, NAS, RAS, and RFC.

radius - A straight line extending from the center of a circle to its edge, or from the center of a sphere to its surface. See also bend radius and radian.

Radome - A cover for a radio antenna, typically used in public broadcast applications.

RADSL (Rate-Adaptive DSL) - A version of asymmetrical digital subscriber loop, where the modems test the line at start up and adapt their operating speed to the fastest the line can handle. RADSL has a maximum downstream transfer rate of 9 Mbps and a maximum upstream rate of 1 Mbps.

RAID (Redundant Array of Inexpensive Disks) - A hard-drive control technology that is intended for servers. RAID links individual drives together, enabling them to act as one storage device, or back each other up via several different storage schemes. One storage scheme is disk striping, which shares data among disks, but does not provide disk-failure protection. RAID provides failure and back-up through disk mirroring, and multiple striping duplicate data to two of many disks. The four most popular types of RAID configurations are: RAID Level 0, which provides data striping only; RAID Level 1, which provides disk Mirroring; RAID Level 3, which stripes data and uses one disk for error correction should one of the others fail; and RAID Level 5, which provides for data striping and stripe error correction. Thus, RAID Level 5 is the best-performing RAID configuration.

Rain Attenuation - The degradation of a radio signal (particularly in the microwave region) because of rain. The rainfall average and density of the rainfall is the determining factor (along with fog, which attenuates radio much more severely) in the distance that a radio (microwave link) can send a signal. Typical ranges for the dry climate regions of the United States are as much as 6 miles, and as little as one mile for the wetter regions (for a 7-watt transmitter).

rain fade - Radio signal attenuation caused by rain. Rain fade is a factor at frequencies above 8 GHz and can be especially serious at frequencies above 11 GHz. Rain fade is sensitive to the rate of rainfall, the size of the raindrops, and the length of exposure as related to the length of the transmission path. See also attenuation. See also rain attenuation.

rain-barrel effect - The echo effect caused by signal reflection. In a real-time voice application, the effect is much like talking into a rain barrel. If you would like to experience the effect, but do not have a rain barrel handy, any barrel will do. See also echo.

Raised Floor - Many computer and telecommunications rooms have a raised floor. The raised floor is a very sturdy framework of iron, with heavy 1 in. tiles placed into the framework. The tiles are easily removed and replaced with a suction cup. The raised floor is used as a giant “duct” to move and run connecting cables through, and it is also used as an airway to pump cool air through the equipment. Instead of cooling a room, cool air is blown under the floor, where it finds its way into the equipment through holes in the floor. The holes are cut into the floor when the equipment is installed.

rake receiver - An antenna system that comprises a set of four receivers, or fingers, that work in a coordinated way to gather signal elements much like the tines of a garden rake work together to gather leaves. Each finger gathers a faded, or attenuated, signal element at a separate moment in time. The receiver employs spatial diversity and time diversity, combining and correlating the results of all four fingers to optimize the signal, thereby countering the effects of multipath fading and delay spread. Code-division multiple access (CDMA) systems employ rake receivers to deal with issues of multipath interference (MPI). See also antenna, attenuation, CDMA, delay spread, MPI, multipath fading, spatial diversity, and time diversity.

RAM (Random-Access Memory) - See Random-Access Memory.

Ram Hook/Ram Horn - A hardware attachment used to hold ASW (Aerial Service Wire) drop clamps in aerial-span applications Ram Horn (left) Mast Clamp (right)

Raman amplifier - A type of amplifier used in long haul, single-mode (SMF) fiber optic transmission systems (FOTS). Raman amplification usually occurs throughout the length of the transmission fiber itself in a process known as distributed amplification, rather than in a discrete amplification, or lumped amplification configuration such as that employed by an erbium-doped fiber amplifier (EDFA). Raman amplification occurs as a high-energy pump wavelength is sent in the reverse direction from the output end of the fiber span, where the incoming signal is weakest.The pump wavelength, which generally is in the 1450 nm range (E-Band), interacts with and excites atoms in the crystalline lattice of the fiber core.The atoms absorb the photons, and quickly release photons with energy equal to the original photon, plus or minus atomic vibration. In other words, a frequency/wavelength shift occurs as the pump wavelength propagates along the fiber in the reverse direction.The energy lost in the pump wavelength shifts to longer-wavelength (within about 100 nm) signals, generally in the 1550 nm window (C-Band), in the forward direction, thereby serving to amplify them. Raman amplifiers offer the advantage of amplifying signals in the broad range extending from 1300 nm to 1700 nm. Further, they perform better than EDFAs in terms of signalto-noise ratio (SNR). Raman amplifiers often are used as preamplifiers to enhance the performance of EDFAs in dense wavelength division multiplexing (DWDM) systems. See also core, discrete amplification, DWDM, C-Band, E-Band, EDFA, FOTS, photon, propagation, SMF, SNR, wavelength, and window.

Rambus “D” RAM (RDRAM) - A newer dynamic random-access memory technology that allows for far greater access speeds than the previously popular SDRAM. At 600 MHz, RDRAM is about six times faster than SDRAM. The package that RDRAM comes in is a small PC board like SDRAM, only it is called a RIMM (Rambus In-Line Memory Module).

Rambus In-Line Memory Module (RIMM) - The package that RDRAM comes in. See Rambus “D” RAM.

RAMDAC (Random-Access Memory Digital-to-Analog Converter) - An integrated circuit that is commonly incorporated into video cards for personal computers. The RAMDAC converts digital images into analog video signals that a monitor can display.

RAN - 1. Recorded Announcement, a term used in IVR and ACD call-flow analysis. If you like, you can call the recorded greeting on your answering machine a RAN. For a photo of a digital announcer that stores RAN messages, see Digital Announcer. 2. Return Authorization Number, also called RA (Return Authorization), or RMA (Return Material Authorization). A reference number in the advance-replacement process. If you receive a shipment from a distributor or manufacturer and a part is defective, you call the distributor/manufacturer and they give you an RA or RMA number to place on the package when you send it back to them. They, in turn, send you a replacement immediately.

random noise - Noise comprising large numbers of frequent, transient impulses, or disturbances, occurring at statistically random time intervals.Thermal noise is a form of random noise.

Random-Access Memory (RAM) - Electronic memory is available in two families, ROM (Read-Only Memory) and RAM (Random-Access Memory). Memory devices are made from two different technologies, Bipolar (TTL) and MOS (Metal-Oxide Semiconductor). Memory is stored by a technique called writing and retrieved by a technique called reading. ROM devices can only be read and are programmed during manufacture. PROM (Programmable Read-Only Memory) devices can be programmed at a later date by an electronics reseller or electronic assembler for a special application using special equipment. Special ROM devices called EPROMs (Erasable Programmable Read-Only Memory) can be electronically erased and re-used. RAM has read and write capability. The term random access means that any memory address can be read in any order at any time. The two types of RAM are static and dynamic. Static RAM can hold its memory even when power is removed. Dynamic RAM needs constant power to refresh its memory. For a diagram of the different types of dynamic memory, see Memory.

RAS - 1. Registration/Admission/Status. In H.323-compliant multimedia networks, the protocol that supports communications between terminals (i.e., endpoint devices) and the gatekeeper. See also H.323, gatekeeper, multimedia, and terminal. 2. Remote Access Server. A host computer on a local area network (LAN) and equipped with modems to serve the needs of end users for dial-up access to internal computer resources through the public switched telephone network (PSTN).An RAS also can take the form of purpose-built hardware with either integral modems or ISDN interfaces.An RAS generally is associated with a Remote Authentication Dial-In User Service (RADIUS) server that performs authentication, authorization, and accounting functions to ensure network security. See also authentication, authorization, ISDN, LAN, modem, NAS, PSTN, RADIUS, and security.

raster - The pattern of uniformly spaced horizontal scan lines that cover the display space of a device, such as a computer monitor or television monitor.Within each line are pixels (picture elements) that can be illuminated individually

rasterize - To scan a document to convert an image into a form suitable for display on a computer monitor or printout. In telecommunications, hard copy documents are rasterized by a facsimile machine prior to transmission. In computing, documents are rasterized prior to electronic processing or storage.

rate adaption - See dynamic rate adaption.

Rate Adaptive - A type of data protocol that is capable of “testing” the telephone circuit for the fastest possible transmission rate, then transmitting at that rate. This test is done using a “ping” packet similar to that used in DSL (Digital Subscriber Loop). DSL is a rate adaptive protocol.

Rate Design - A term that refers to the way utility companies figure a way to charge money for their services. Rates are designed to be affordable for everyone (PUC/PSC requirement). A good example of rate design is the way that the telephone companies charge extra money for business lines to offset the costs of residential lines. How far the offset is and how much one rate is subsidized for the other is the rate design.

Rate Elements - The individual charges and fees for a service. For instance, all of the rate elements are listed on your phone bill: the local service charge, dial tone, 911 service, etc. All of these parts of the telephone company have been separated by the FCC and billed for separately by law.

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.

Rate-Adaptive ADSL (RADSL) - A version of asymmetrical digital subscriber loop, where the modems test the line at start up and adapt their operating speed to the fastest the line can handle. RADSL has a maximum downstream transfer rate of 9 Mbps and a maximum upstream rate of 1 Mbps.

rates and tariffs - See tariff.

RATT (R1022 ATM Technology Testbed) - See RACE.

ray - A thin beam of radiant energy, especially light.

Rayleigh Fading - Rayleigh Fading is a form of signal reduction or loss because of a receiver picking up the same signal from multiple directions. The signal commonly arrives from multiple directions because of reflections from buildings when there is no line-of-site path (receiving reflections of the same signal is also referred to as multipath reception). When the signals meet, they add or subtract each other, causing an irregular signal strength. Rayleigh fading is a common reason for geographical “dead spots” in cellular service networks.

Rayleigh Scattering - The scattering of light in a fiber-optic cable because of impurities in the glass of the fiber. It has a similar effect to what a lamp shade has on a light bulb, just not as drastic.

RBOC (Regional Bell Operating Company) - At the time of divestiture, there were 22 BOCs, grouped into seven Regional Bell Operating Companies (RBOCs). For a listing of the BOCs and RBOCs, see Regional Bell Operating Company.

RCA (Regional Calling Area) - The geographical area that a telephone company serves.

RCA Connector - A plug first developed and used by RCA (Radio Corporation of America). These plugs are very common in audio- and videopatch applications. If you have a CD player and a separate tuner/amplifier, the cord that connects the two most likely has RCA connectors.

RCC (Radio Common Carrier) - A cellular/PCS service provider or paging company. A company that is in the business of providing one-way (paging) or two-way (mobile phone) radio services to individuals, rather than communities. Broadcast TV or radio stations are not radio common carriers.

RCDD (Registered Communications Distribution Designer) - A well-known industry certification/training program offered by BICSI (Building Industry Consulting Service International). The RCDD certification is designed to educate professionals in the area of physical network distribution, including twisted pair and optical media. The RCDD is sometimes referred to as a BICSI (pronounced “bik-see”) certification. More information can be found regarding BICSI certifications at http://www.bicsi.org.

RCP (Remote Copy Protocol) - A 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.

RDF (Resource Description Framework) - A W3C specification that integrates a variety of applications, using XML as an interexchange syntax. See also RDF Site Summary, W3C, and XML.

RDF Site Summary (RSS) - See RDF and RSS.

RDRAM (Rambus “D” RAM) - A newer dynamic random-access memory technology that allows for far greater access speeds than the previously popular SDRAM. At 600 MHz, RDRAM is about six times faster than SDRAM. The package that RDRAM comes in is a small PC board like SDRAM, only it is called a RIMM (Rambus In-Line Memory Module).

Reactance - Reactance is the resistance that a component gives to an AC or fluctuating DC current. The two components that cause reactance are inductors (coils) and capacitors. (Reactance is also caused by other electronic conditions where it is not useful. All wire and electronic components possess a small amount of reactive properties, e.g., twisted-pair wire causes signal attenuation because of the inductance of the copper wire and the capacitance of the two adjacent wires.) The difference between resistance and reactance is that resistance is always the same, regardless of the voltage amplitude or frequency applied to the resistive device. The reactance of a component changes along with frequency changes, the speed at which an AC current changes direction. The higher the frequency applied to an inductor, the higher the reactance or resistance to that frequency. The reason that coils of wire cause reactance is that as electricity flows through them, they force the electricity to create a magnetic field every time it changes direction. A perfect inductor has zero reactance to a DC current, and has a specific reactance or resistance to every frequency of AC current. Each coil (inductor) has a value in henries. The higher the number of henries, the more it will resist AC or fluctuating DC. Coils are used to filter out (“choke” out) DC fluctuations in power supplies. They are also used to help tune in radio or other frequencies.

Read-Only Memory (ROM) - See Random-Access Memory.

Real Time Control Protocol (RTCP) - See RTCP.

Real Time Transport Protocol (RTP) - See RTP.

Real Time - A reference to the relationship of events in a communications channel, machine, or PC. Real time means that the inside of the machine is synchronized with real-world time that you and I live in. Another word for this is isochronous, which means “in time.” Newer technology has changed this.

Real-Time Streaming Protocol (RTSP) - An application-level protocol designed to utilize TCP/IP to enable real-time communications over the Internet, such as voice over IP.

real-time variable bit rate (rt-VBR) - See rt-VBR.

Really Simple Syndication (RSS) - See RSS.

Rebiller - A telephone company that buys a telephone service from a facilities based telephone company and resells it. A rebiller attempts to add value to the original long-distance company’s service by providing better customer service and customized technical expertise. The rebiller gets a discount from the original long-distance company, typically about 10%. Rebilling is also known as Type-III service, where all circuits (telephone lines) are type III.

Rebooting - To restart a computer by turning it off and turning it on again. The two ways to re-boot a computer are a hard boot and a soft boot. Hard booting is manually turning off the computer to force the microprocessor to reset. Soft booting is done by pressing Ctrl-Alt-Del at the same time. This direct code sends a positive pulse to the reset of the computer. However, it will sometimes not work if the computer’s keyboard is locked up with the rest of the components.

Receiver Off Hook (ROH) - The condition of a telephone set being left off the hook, with no numbers dialed, or left off the hook after a conversation has been completed. This causes the central office to disconnect the voltage from the telephone line, which saves electricity. When the receiver is placed back on the hook, the telephone line does not become activated instantaneously. The dial tone can take one to two minutes to return. ROH is a common test result in telephone company mechanized loop testing.

Receiver - 1. The part of a telephone handset that you talk into. The receiver has a microphone inside it. 2. A radio device that is connected to an antenna and filters and detects carrier frequencies and signals modulated on them. For more information, see Modulation and AGC.

recognition and flagging - An error control mode in which detected errors are flagged by the receiving device, but there is no mechanism for error correction. Rather, error correction requires a human-tomachine request for retransmission. Recognition and flagging is primarily used in networks involving dumb terminals with no means of buffering or retaining information transmitted and which, therefore, are unable to retransmit errored data. Parity checking is an example of recognition and flagging. See also buffer, dumb terminal, error control, FEC, parity check, and recognition and retransmission.

recognition and retransmission - An error control mode that provides for retransmission of errored data packets.The error detection logic can be implemented not only in the receiving device but also in intermediate routers, switches, and other intelligent nodes.The device detecting an error issues a retransmission request to the device immediately upstream, or perhaps to the original transmitter, which holds some amount of data in a buffer until it has received an indication that the data either was received correctly or that the data was received in an errored state. If the upstream device receives no indication either way within a specified time interval, it assumes that the data was lost in transit and automatically initiates a retransmission through a protocol known as automatic repeat request (ARQ).As examples, recognition and retransmission is used in X.25 networks, and by applications running the Transmission Control Protocol (TCP) over Internet Protocol (IP) networks. Block parity is an example of recognition and retransmission. See also ARQ, block parity, buffer, checksum, error control, FEC, IP, recognition and flagging, TCP, upstream, and X.25.

recommended standard (RS) - See RS.

record communications service - A service designed or used primarily to transfer information that originates or terminates in written or graphic form. Examples of record communications services include telex and TWX.

Recorded Announcement (RAN) - 1. Recorded Announcement, a term used in IVR and ACD call-flow analysis. If you like, you can call the recorded greeting on your answering machine a RAN. 2. Return Authorization Number, also called RMA (Return Material Authorization) or RA (Return Authorization). A reference number in the advance-replacement process. If you receive a shipment from a distributor or manufacturer and a part is defective, call the distributor/ manufacturer and they will give you an RA or RMA number to place on the package when you send it back. They, in turn, send you a replacement immediately.

Rectifier - A device to convert AC power to DC power, also called a diode. An electronic semiconductor device that, simply put, only conducts electricity in one direction. Whether or not the device conducts depends on which direction the device is “biased.” Diodes are used to change Alternating Current (AC) to Direct Current (DC). If a more positive voltage is applied to the anode lead of the diode, then the diode simply acts like a wire. If the more positive voltage is applied to the cathode lead, then it acts like there is no connection. The following illustration shows the schematic symbols of the first diode, which was a vacuum tube, and a solid-state silicon diode. Figure R.3 is a pair of diodes converting AC to DC. 2. A DC power source.

red sunset - See Rayleigh scattering.

redirected PVC - In frame relay, an inactive permanent virtual circuit (PVC) that can be activated very quickly to direct traffic around a point of failure in the network or in the access loop. A redirected PVC also can be used to redirect traffic to a backup data center should the primary data center suffer a failure. See also frame relay, local loop, and PVC.

Redundancy - To have one main and one back-up. SONET equipment is capable of being configured in a redundant manner, with two fiber-optic routes (in a ring) and duplicates of the electronic cards that control the communications transmission. Many PBX systems are capable of being configured with redundant CPU and memory cards. The idea behind redundancy is that if one device fails, the other will take over, without a loss of service.

Redundant Array of Inexpensive Disks (RAID) - A hard-drive control technology that is intended for servers. RAID links individual drives together, enabling them to act as one storage device, or back each other up via several different storage schemes. One storage scheme is disk striping, which shares data among disks, but does not provide disk-failure protection. RAID provides failure and back-up through disk mirroring, and multiple striping duplicate data to two of many disks. The four most popular types of RAID configurations are: RAID Level 0, which provides data striping only; RAID Level 1, which provides disk Mirroring; RAID Level 3, which stripes data and uses one disk for error correction should one of the others fail; and RAID Level 5, which provides for data striping and stripe error correction. Thus, RAID Level 5 is the best-performing RAID configuration.

Reed-Solomon (RS) - A block coding algorithm for forward error correction (FEC). Reed-Solomon works by viewing the data as a polynomial, which it analyzes and organizes into symbols, which it groups into blocks, to each of which it adds parity bits to form codewords. For example, RS (255,223) is byteoriented, working with 8-bit symbols. Each codeword contains 255 code word bytes comprising 223 data symbols and 32 parity symbols. See also algorithm, block, block code, byte, code, FEC, parity bit, and symbol.

Reference Clock - Also called a bits clock. A device that provides a timing pulse in the form of a 1-0-1-0-1-0-1-0 bit stream. Bits clocks are used extensively in SONET networks. The bits clock provides the timing pulse that everything in the network synchronizes itself to.

Reference Model - The ITU-T specifications for integrated services digital network (ISDN) use an alphabetical reference model to describe the various Reference Points (i.e., connection points or interfaces) on the customer side of the network.Those points are R, S,T, U, and Q. See also Reference Point R, Reference Point S, Reference Point T, Reference Point U, and Reference Point Q.

Reference Point Q - Also known as the Q interface.The ISDN point of reference for the QSIG interface between two ISDN PBXs in a private network. See also ISDN, PBX, and QSIG.

Reference Point R - Also known as the R interface. The ISDN point of reference for the interface between non-ISDN compatible terminal equipment (TE2) and a terminal adapter (TA) that connects on the network side to an S interface of an NT2. See also ISDN, NT2, TA, and TE2.

Reference Point S - Also known as the S interface.The ISDN point of reference for the interface between an ISDN terminal and the NT2, which is the user side of the local loop.The S interface serves to distinguish between terminal equipment and network-related functions.The S interface is defined as a passive bus on Cat 5 cable for up to 8 NT2 devices, which are intelligent and ISDN-compatible. See also Cat 5, ISDN, and NT2.

Reference Point T - Also known as the T interface.The ISDN point of reference for the four-wire connection between NT1 and NT2. See also four-wire, ISDN, NT1, and NT2.

Reference Point U - Also known as the U interface.The ISDN point of reference for the demarcation point (demarc) between the public network local loop and the customer premises equipment (CPE) or NT1. See also demarc, CPE, ISDN, local loop, and NT1.

Reference Point V - Also known as the V interface.The ISDN point of reference for the point of interface at the network side of the connection between the line termination or loop termination and the exchange termination. In other words, it is the point between the circuit terminating equipment and the ISDN central office (CO).As the V interface exists only if the CO does not have embedded circuit terminating equipment, it is unusual in contemporary ISDN-compatible COs. See also CO and ISDN.

reflection grating - A type of diffraction grating comprising grooves ruled into a surface that can be either plane or concave. In a distributed feedback laser (DFB laser), a diffraction grating with a concave surface serves to focus light without affecting the spectra.This approach is much more effective than the mirror technique employed with a Fabry-Perot laser and vertical cavity surface-emitting laser (VCSEL). See also DFB laser, diffraction, diffraction grating, Fabry-Perot laser, and VCSEL.

reflection - The act or process of redirecting electromagnetic energy along a new path, using a conductive surface or impedance discontinuity. At a surface, the angle of the reflection equals the angle of incidence, i.e., the angle at which the incident signal strikes the plane surface of the obstacle.At the extreme, the signal reflects back towards its point of origin. See also angle of incidence and refraction.

reflector - A passive device that simply redirects radiant energy, rather than amplifying it or otherwise acting on the signal.

ReFLEX - See FLEX.

Refraction - Refraction refers to the wavelike nature of light. When light travels from one media, such as air, into another media, such as water, it bends. This is why when you look into a swimming pool, the bottom looks very distorted. Fiber-optic technology is based on the fact that light refracts (or bends) as it travels from one media to the next. A single fiber-optic strand consists of many different kinds of glass. The core is one kind and the cladding consists of many layers of glass that have different “levels” of refraction and cause light to gradually refract or bend back to the center as it travels down the fiber.

Refractive Index - The refractive index of a material refers to how much light refracts (bends) when it travels from a vacuum into the material at an angle. For a diagram and more details, see Refraction.

refresh rate - The rate at which a video monitor is completely renewed or updated.

Refurbished - Electronic equipment that has been repaired and cleaned, or remanufactured.

regenerative repeater - See repeater.

Regenerator - Also known as a repeater. A device that is used to take a signal that has traveled a long distance and make it new again. Repeaters can be coils of wire, which are used in the public telephone network for voice (POTS) lines, or they can be electronic, taking an electronic signal that has been attenuated over a long distance, reproducing it, then retransmitting it.

Regional Bell Operating Company (RBOC) - At the time of divestiture, the 22 BOCs were grouped into seven Regional Bell Operating Companies (RBOCs):

BOCs : Bell Telephone Company of Nevada, Illinois Bell Telephone Company, Indiana Bell Telephone Company, Michigan Bell Telephone Company, New England Telephone and Telegraph Company, US West Communications Company, South Central Bell Telephone Company, Southern Bell Telephone and Telegraph Company, Cincinnati Bell Company, Mountain Bell Telephone Company, Mountain States Telephone and Telegraph Company, Southwestern Bell Telephone Company, The Chesapeake and Potomac Telephone Company of Maryland, The Bell Telephone Company of Pennsylvania, The Chesapeake and Potomac Telephone Company of Virginia, The Chesapeake and Potomac Telephone Company of West Virginia, The Diamond State Telephone Company, The Ohio Bell Telephone Company, The Pacific Telephone and Telegraph Company, New Jersey Bell Telephone Company, Wisconsin Telephone Company.

RBOCs : Ameritech, Bell Atlantic, Bell South, NYNEX, Pacific Telesis, Southwestern Bell, US West.

Regional Internet Registry (RIR) - See RIR.

Register - Also called a shift register. An electronic circuit used for temporarily storing memory in a serial format (Fig. R.6). Shift registers are commonly used in the serial-to-parallel conversion for data transmission. Bits are clocked into the register one at a time, then clocked out to their destination when they are needed. Each memory segment of a register is typically an RS (Reset-Set) flip-flop.

Registered Communications Distribution Designer (RCDD) - A well-known industry certification/training program offered by BICSI (Building Industry Consulting Service International). The RCDD certification is designed to educate professionals in the area of physical network distribution, including twisted pair and optical media. The RCDD is sometimes referred to as a BICSI (pronounced “bik-see”) certification. More information can be found regarding BICSI certifications at http://www.bicsi.org.

registered port - A port that can be used by ordinary user processes or programs on most systems and can be executed by ordinary users. Registered port assignments, numbered in the range 1,024 through 49,151, are used with the User Datagram Protocol (UDP) to the extent possible. Registered ports are registered by the Internet Corporation for Assigned Names and Numbers (ICANN) as a convenience to the Internet community. See also dynamic port, ICANN, port, UDP, and well-known port.

Registered Terminal Equipment - Any line or telephone service that is installed by a telephone company is terminated to registered terminal equipment. The different levels of registered equipment are as simple as an RJ45 (Registered Jack 45) or as complicated as a DSX hand-off point in a colocation.

registration authority (RA) - See RA.

Registration Jack (RJ) - The prefix to many telephone company connection and interface standards.

Registration/Admission/Status (RAS) - See RAS.

regular pulse excitation linear predictive coding (RPELPC) - See RPELPC.

Regulation, Power - A device that takes an unstable power source, such as public utility power, and reproduces the voltage/amperage with electronics. The electronics in a power regulator are a controlled environment that produces the desired power signal. The street power provides the energy for the device (power regulator) to do this.

Regulation, Telco - The RBOCs, CLECs, long-distance companies, and competitive-access providers are all regulated by the Public Utilities Commissions (PUC) of their respective areas in some fashion. The Bell companies are heavily regulated to a disadvantage to enable new telephone companies to become established. One of those disadvantages is that they are forced to charge higher rates for their services in competitive areas. This allows the new companies to attract customers with a price advantage. Many new companies do not take advantage of the price regulation, because their networking equipment is of latest technology (SONET 100%, in many cases), which therefore carries a higher value to customers. Competitive Local Exchange Carriers (CLECs) become regulated for pricing when they reach a certain number of customers or percentage of market share. All communications companies, new and old, must demonstrate to the PUC that they are capable and willing to provide acceptable service to the public.

regulation - From the Latin regula meaning rule. Rule or order established by governmental bodies and having the force of law.

Relational Data Base - A data-base application (software program) that tracks data, based on relationships. It works very similar to a manual paper-filing system, with different categories and cross references. A good example is: There are many houses. Each house has many (one or more) residents. If a data base were created for this, each house would be listed and people would be related to the house. People make many telephone calls. The calls people make can be related to the people that make them. The way that a computer program would think, if queried, to find every person that dialed the phone number 1-602-555-1212, is as follows. It would scan through the data base and, as it found the phone number, it would list the relational items to it. More simply stated, it would list every person and house that dialed that phone number.

Relay Rack - Large racks that got their names from a time when they were used as a mounting platform for electromechanical relay circuits in telephone central offices. Their standard size is 7 feet tall by 22 inches wide. Relay racks are available in a 19-inch wide size as well.Relay Rack Large racks that got their names from a time when they were used as a mounting platform for electromechanical relay circuits in telephone central offices. Their standard size is 7 feet tall by 22 inches wide. Relay racks are available in a 19-inch wide size as well.

Relay - An electromechanical switch (Fig. R.7). Relays are used in electronic and electrical circuits as switches. A relay consists of a coil of wire wrapped around a thin cylindrical-shaped piece of iron, called a core. When electricity flows through the coil, it magnetizes the core, which is close to a pair of electrical contacts. The magnetic field attracts one of the contacts to move and make a connection. A popular application for relays is between a small voltage to run a switch that connects a very large voltage. This is why you can start the motor in a large truck with a small keyed switch. The key applies voltage to a relay, which, in turn, connects a large contact from the battery to the starter of the motor. Relays were used in old central offices (some still in service), called stepper switches. By dialing a rotary phone, you manipulated a vast network of relays and logic circuits to connect your call. Today, relays have been replaced with transistors; in large or heavier applications, they have been replaced with semiconductor devices called SCRs (Silicon- Controlled Rectifiers). However, electromechanical relays still have the special ability to physically isolate one voltage or device from another. They are still used in higher-end home-audio equipment, where if you turn down the volume, then turn on your stereo, after a short pause, you will hear a “click.” That “click” is a relay connecting the output signal voltage to your speakers.

remote access server (RAS) - See RAS.

Remote Authentication Dial-In User Service (RADIUS) - See RADIUS.

Remote Call Forward - A feature of PBX systems that enables users/ subscribers to make calls dialed to their telephone ring to a different telephone of their choice and activate the feature from a different phone. When a user wants to activate the feature, they can dial a feature code, dial their extension, then dial the extension that they would like their calls to ring on. The great thing about this feature is that if you are in a meeting, you can pick up a phone and forward the phone in your office to another co-worker or anywhere else within the PBX system. Some systems allow you to forward your extension to an off-premises telephone number, such as your home. In this case, you can work out of your home, and not miss any calls coming to your extension because they will ring directly to you.

Remote Mini-Fiber Node - A device used in the outside plant portion of cable telephony networks to convert light signals to RF electrical signals. Mini-fiber nodes can be made to be pole mounted or can be placed in hand holes/cable vaults. Because cable-TV networks are far spread and rural, fiber optic is a necessity in extending the bandwidth required to areas distant from head ends. The mini-fiber node provides the means for this extension.

Remote Order Wire - A telephone line that is used to monitor an electronic system. A dial-up maintenance line for a server or mainframe is an order wire.

Remote Shell (RSH) - 1. A UNIX operating system level of access. See also C-Shell and Root. 2. Remote Shell Protocol. It is referred to as R-shell from the similarities in the UNIX command set. An application or subprotocol that allows a user to execute commands on a remote system without having to log into the system. For example, rsh, along with a password (if the network OS supports passwords), can be used to remotely examine the status of network devices without connecting to each communication server, executing the command, and then disconnecting from the communication server.

reorder tone - Synonymous with fast busy. See fast busy signal.

REPACCS (Remote Cable-Pair Cross-Connect System) - A remotecontrolled/ automated cross box. A less-sophisticated DCS (Digital Cross-Connect System). In certain areas of cities that are hazardous for telco workers, REPACCS systems are implemented so that F1 and F2 cable pairs can be cross connected remotely.

repeat dial - Synonymous with continuous redial. See also continuous redial.

Repeater Coil - A radio-type transformer that is used to amplify voice signals on copper twisted-pair telephone wires. Repeater coils have a typical inductance value of 33 mH and are placed every 3000 to 5000 feet.

Repeater - Also known as a regenerator. A device that is used to take a signal that has traveled a long distance and make it new again. Repeaters can be coils of wire, which are used in the public telephone network for voice (POTS) lines or they can be electronic, taking an electronic signal that has been attenuated over a long distance, reproducing it, then retransmitting it.

Request for Comment (RFC) - See RFC.

Request To Send (RTS) - 1. After a modem receives a CD (Carrier Detect) signal from another modem, the next step is to send some data. Before it sends data, it sends an RTS (Request To Send). After it receives a CTS (Clear To Send) from the far-end modem, it begins sending data. 2. A control signal that has a dedicated wire in the RS-232 protocol. When the far device places a logic “one” or 5-V voltage on this wire, it enables the near modem to initiate a transmission.

Rerouting - To change the physical path or medium of a communications signal. Rerouting is a part of SHARP (Self-Healing Alternate-Route Protection) service from telephone companies over their SONET networks. If a cable is cut, the electronic equipment reroutes the transmission with very little or no interruption in service. If you are talking on a voice line while a fiber is cut on a SONET ring network that is very busy and fully utilized, you might hear a very light click sound.

Resale Carrier - A long-distance company that leases long-distance facilities and sells service on them. Sprint and MCI are resellers in some areas; in some areas, they have their own switches, fiber-optic lines, and microwave equipment. In those areas, they are facilities-based carriers.

Réseaux IP Européens Network Coordination Center (RIPE NCC) - See RIPE NCC.

Reseller - Also called an aggregator. A long-distance or cellular/PCS reseller. They sign up with a long-distance company as a reseller and all their customers are “aggregated” together for a bulk discount. The longdistance or cellular company provides the service and does the billing. The advantage to the long-distance company is that they have more people pushing their long distance. The advantage to the customer is the value-added service and personal consulting of the aggregator.

Reset - See Rebooting.

Resilient Packet Ring (RPR) - See RPR.

Resistance - The unit of resistance is the ohm, abbreviated/represented by the Greek letter omega (�). Resistance is just what its name depicts, resistance to electric current flow. A 100-W 120-V household light bulb has about one ohm of resistance. The more resistance in a circuit, the less current is allowed to pass through it.

Resistor Color Code - See Appendix F. Resistors have four color bands. They are regarded to as the first, second, third, and fourth bands. The first band is the closest to one side of the resistor and the following bands count to the inside. The first band indicates the first integer of the value of resistance. The second band indicates the second integer of the value of resistance. The third band indicates a multiplier or number of zeros to be placed after the first two band numbers.

Resistor - An electronic component/semiconductor usually made from carbon. Resistors are usually used to limit current flow through a circuit or create RC/RL (resistor-capacitor/resistor-inductor) frequency filters.

resolution - The definition, sharpness, or level of detail of the reproduction of an image. Resolution is directly related to the number and density of the dots of color (black, white, and perhaps other colors). Group III facsimile specifications, for example, provide a number of options, expressed as horizontal lines per inch (lpi) in terms of scanning (input), and linear dots per inch (dpi) in terms of sensing and printing (output).The actual (and nominal) fax industry standards are as follows:

• Standard: 98 × 203 (100 × 200)

• Fine: 196 × 203 (200 × 200)

• Superfine: 392 × 203 (400 × 200)

In video images, resolution is determined by the number and areal density of the pixels, or pels (picture elements), which essentially are dots of picture similar to the dots in half-tone printing.

Resonance - A circuit is resonant if the inductive reactance and capacitive reactance are equal. This condition occurs for all inductor/ capacitor circuits. The frequency at which the resonance happens is determined by the value in mH of the coil and the value of the capacitor in �F.

resource management cell (RM-Cell) - See RM-Cell.

Resource ReserVation Protocol (RSVP) - A transport-layer protocol that is intended to provide quality-of-service transmission levels in conjunction with TCP/IP over the Internet. The RSVP protocol makes the sender of data responsible for notifying the receiver that a call is to be made (or data to be sent) and what QOS (Quality of Service) will be needed. The responsibility of selecting the resources or path by which the transmission will take is given to the receiver or called party. RSVP is modeled to work with IPv6 and Ipv4.

Retrofit - To make older equipment work with newer equipment. Retrofit is a term commonly used among telephone company network technicians in reference to upgrading telephone equipment. Return Authorization Number (RAN) See RAN.

Return to Zero (RZ) - A transmission format where each positive bit returns or drops to a zero value during its timing period. The dropto- zero format assists in timing/synchronizing of the transmission signal.

Reverse Battery Supervision - A form of answer supervision. An inband signaling method, if a telephone call goes from one central office to another (or PBX), the originating central office needs to know when the call has been answered so that a billing cycle can begin. The terminating central office briefly reverses the voltage on the connecting trunk line as a signal.

Reverse Channel - Also called a backward channel. The channel that flows upstream in an asymmetrical (uneven) transmission. An asymmetrical communications transmission that is characterized by one direction being very fast, compared to the other. Cable TV is an example of asymmetrical communication. The cable TV head end sends massive amounts of video and audio information down a coax one way and the cable TV set-top decoder boxes send small amounts of ID and status information the other way back to the head end over the same coaxial connection. Sometimes asymmetrical channels are referred to as “upstream” for the slow channel and “downstream” for the fast channel, or “forward” for the fast channel and “backward” for the slow channel.

RF (Radio Frequency) - Any electromagnetic frequency that is above the range of human hearing. Most licensed radio frequency transmissions range from 500 kHz (500,000 Hz) to 300 GHz (300,000,000,000 Hz).

RF Choke - A coil of wire that filters out high frequencies.

RF Splitter - Used to make a junction point or split a signal so that it will travel down multiple paths over coax. Also called a splitter and UHF/VHF splitter.

RFC (Request For Comment) - The official document by which the Internet Activities Board (IAB) and the Internet Engineering Task Force (IETF) publish standards, protocols, best practices, or other information relative to the operation of the Internet.The format dates to the early days of the ARPANET in which authors circulated hard copies of their proposals to their colleagues and requested their comments. In the more formal context of contemporary Internet administration, requests for comments actually are made in an Internet Draft document. See also ARPANET, IAB, IETF, and Internet.

RFI (Radio Frequency Interference) - See Radio Frequency Interference.

RFP (Request For Proposal) - Also called RFQ (Request For Quotation). A formal invitation that a company or individual gives to other individuals or companies, to bid or price a service.

RG (Radio Guide) - The RG numbering system of coaxial cable (coax) refers to the fact that the RF (Radio Frequency) signal is guided down the center conductor of the cable system.The RG numbering system dates to WWII United States military specifications and has no real contemporary significance other than type designators. Each RG number does, however, specify impedance, core conductor gauge (AWG) and type, outside diameter (OD), and other physical attributes of the cable. See also coaxial cable.

RG Number	Center Wire Gauge	Impedance (Ω)	Outside Diameter (OD)	Core Type	Example Applications
RG-6/U	18 AWG	75 ohms	.332 in.	Solid	CATV, cable modems, DBS TV
RG-8/U	10 AWG	50 ohms	.405 in.	Solid	10Base5 Ethernet, Ham radio
RG-58/U	20 AWG	53.5 ohms	.116 in.	Solid	10Base2 Ethernet, Ham radio
RG-58C/U	20 AWG	50 ohms	116 in.	Solid	RG-58A/U Military Spec
RG-58A/U	20 AWG	50 ohms	116 in.	Stranded	10Base2 Ethernet, CATV
RG-59/U	20 AWG	75 ohms	146 in.	Solid	Ham Radio, CCTV
RG-62/U	22 AWG	93 ohms	.146 in.	Solid	ARCnet, IBM cabling system

Coaxial Cable Types

RG-58 A type of coaxial cable that has a transmission impedance of 50 �. It is used primarily in LAN applications and wired in a bus physical topology. For more information on different types of coaxial cable, see Coax and Characteristic Impedance.

RG-59 - A type of coaxial cable designed for television antenna use that has an impedance of 75 ohms. For more information on different types of coaxial cable, see Coax and Characteristic Impedance.

RG-62 - A type of coaxial cable with a transmission impedance of 93 ohms. It is primarily used in LAN applications and wired in a bus physical topology. ARCnet utilizes RG-62 as its transmission media. For more information on different types of coaxial cable, see Coax and Characteristic Impedance.

RG-8 - A type of coaxial cable that has a transmission impedance of 50 ohms. For more information on different types of coaxial cable, see Coax and Characteristic Impedance. For a photo of RG-8, see DIN Connector.

RG-U - The military designation for general-use coaxial cable.

RHC (Rural Health Care Corporation) - See RBOC and Rural Health Care Program.

RI (Ring Indicator) - An indicator on a modem that indicates that a ring voltage (90 volts AC) is present on the telephone line to which it is connected.

ribbon cable - 1. A type of horizontal cable comprising many metallic wires lying side by side, in parallel, forming a flat, ribbon-like structure. Ribbon cables are used indoors under carpeting, for reasons of safety and aesthetics, as they lie flat. Ribbon cables can be used only in straight cable runs, as they do not flex sideways. See also horizontal cable. 2. A type of outside plant (OSP) fiber optic cable comprising unbuffered (i.e., uninsulated) acrylate-coated glass optical fibers (GOF) lying side by side, in parallel, and encased in a plastic material to form a flat, ribbon-like structure. A distribution cable typically contains a single ribbon of 6 or 12 fibers.A long haul cable may contain many such ribbons, stacked on top of each other. Along a high traffic physical cable route, it is not unusual to find a cable containing 12 ribbons of 12 fibers, each, for a total of 144 fibers.The advantage of ribbon fiber is in its ease of handling and splicing.As the fibers are not individually buffered and sheathed, they are less bulky, therefore, more manageable. Also, a technician can splice the entire ribbon at once, rather than having to splice each individual fiber. See also optical fiber.

Rich Site Summary (RSS) - See RSS.

Rich Text Formatting (RTF) - See rich text.

rich text - Textual data (letters, numbers, and punctuation marks), including formatting, such as italics, bold, and color other than the black and grayscale in which this book is printed. Rich text often conforms to the Rich Text Formatting (RTF) standard developed by Microsoft Corporation. RTF allows a word processing program to create a rich text file encoded with all necessary formatting instructions, and without any hidden codes.An RTF-encoded file also can be transmitted between applications on a computer and across a network without loss of formatting because it consists only of standard text characters. See also plain text.

right of way - The right, established by common or statutory law, of passage over an area of land.A public right of way grants passage to all and essentially is a public easement that allows the construction of roads over it and public utilities (e.g., electrical, gas, telephone, sewer, and water) over and through a narrow strip of land. See also utility.

RIMM (Rambus In-Line Memory Module) - The package that RDRAM comes in. See Rambus “D” RAM.

ring again - A CLASS service feature of the public switched telephone network (PSTN). The feature allows a calling party who encounters a busy signal to request network notification when the called line becomes available.When both lines become available, the network calls the calling party back with a distinctive ring tone. When the caller lifts the handset, the network automatically redials the call. See also CLASS and PSTN.

Ring Banding - Some pic cable comes with no ring banding, which means that the color code is determined by two wires twisted together (e.g., a white and a blue). Ring-banded cable comes with color rings painted around each wire, and the same twisted pair listed before would be white/blue bands and blue/white bands.

Ring Cycle - The ring cycle for a North American POTS telephone line is two seconds of ringing, then four of quiet. Ringing cycles vary throughout the world.

Ring Generator - A ring generator is the part of a PBX or central-office switch that provides the source of the ring voltage that rings telephones. Ring generators are an individual circuit card in many PBX systems. In some systems, the ring-generation capability is built into the station/ telephone interface cards.

Ring Latency - In a token-ring network, ring latency is the time required for a transmission packet to go all the way around the ring.

ring tone - Also known as ringing signal and ringing tone. An audible indication to the called party of an incoming call.The nature of the ring tone varies. In the United States, Canada, and other countries in the North American Numbering Plan (NANP), the traditional ring tone is generated by two metal bells mounted inside the telephone set.The ringer is activated by a current of approximately 90–110 volts at 20 Hz generated by a central office-based ringing machine and sent across the copper local loop at a cadence of approximately two seconds on and four seconds off. Contemporary telephones generally dispense with metal bells in favor of various microprocessor-generated ringing signals, and there may be several from which to choose. Personalized ring tones recently have become popular, especially with respect to cellular telephones. Dozens of music genres and hundreds of selections are commonly available for both the ring tone of the cell phone and the ringback tone. See also ringback tone.

Ring Topology - A LAN topology (a MAN topology in SONET) that connects all devices on a network in a ring configuration. The data transmitted through the network goes through each device. As the devices receive the data, they check to see if it is intended for them. If it is, then they keep it; if it is not, then they pass it along. Unlike Ethernet star and bus topologies, the ring topology is not contention based; each device gets a specified turn in sending and receiving data.

Ring Voltage - Ring voltage on a POTS telephone line is 90V AC.

Ring-Down Box - Used in building ring-down circuits. A device that you put on each end of a copper twisted pair that provides battery and ring voltages that a central office would. However, no dialing is involved. When you pick up one phone, the one on the other end automatically rings. When the ringing phone is picked up, the lines are connected together with a talk battery and people can talk on both ends, just like a normal telephone call. Tellabs manufactures a wide variety of ring-down devices.

Ring-Down Circuit - A simple telephone line that is made using ring down boxes. See Ring-Down Box.

Ring - One wire in a POTS telephone line. The ring side of the line is usually marked red when terminated and carries the 90V AC ring-voltage signal that makes the telephone ring.

ringback tone - An intermittent audible indication to the calling party that a dialed telephone number is ringing. A ringback tone is a status indicator that the dialed number is available (i.e., not busy), that all connections through the appropriate network or networks between the originating and destination devices either have been made or are available to be made, and that the call can be connected if someone or something answers the call. The call can be answered by a human being if the destination telephone number is not engaged, or if the destination telephone number is engaged, has call waiting service, and a call waiting indicator tone prompted a human being to either abandon the first call or place it on hold in order to answer the second.The call can be answered by a premises-based answering machine or a local or network-based voice processor in the event that the called number does not answer, is busy, or does not answer within a programmable number of rings. The nature of the ringback tone varies by region and country. In the United States, Canada, and other countries in the North American Numbering Plan (NANP), the standard PSTN ringback tone is generated by summing a 440-Hz tone with a 480-Hz tone and applying these to the telephone line in a two-second on and four-second off cadence.The tone combination produces a warbling “ring ... ring ... ring” sound, caused by the 40-Hz beat, or interference due to the difference in frequency, between the two tones.The ringback tone may be generated by the switch serving either the called party or the calling party, but it is not generated by the called telephone instrument or PBX.The ringback tone generally starts and stops at the same rate as the ringing tone of the called telephone, but generally is out of phase, i.e., staggered in time. Personalized ringback tones recently have become popular, especially with respect to cellular telephones. Dozens of music genres and hundreds of selections are commonly available for both the ringback tone and the ringing tone.The service generally is on a subscription basis and carries an additional charge per tone selected. It is possible to select up to 100 or so active ringback tones at any given time, to play different tones for different callers, and to vary the tone by time of day, perhaps to have one tone for business hours and another for all other times. See also ring tone.

Ringer Equivalency Number (REN) - A number that references a device’s load on a telephone line when the line rings. Telephones, modems, answering machines, and other devices connected to telephone lines are required to have this number printed or stamped somewhere on the device, or placed in the device’s literature. A telephone line in North America is capable of driving 5 bells, or 5 devices with a ringer equivalancy number of 1. If a telephone line has more than 5 such devices plugged into it, it may fail to ring when called.

ringing signal - See ring tone.

ringlet - In Resilient Packet Ring (RPR) networks, a small local ring where the larger ring drops traffic off to nodes. See also node, ring topology, and RPR.

RIP (Routing Information Protocol) - A traffic-control method used by routers. RIP was originally developed by Xerox Corporation in the early 1980s for use in Xerox Network Systems (XNS) networks. Cisco Systems has developed their own version of RIP that works well as a standard with other manufacturers’ routers and has additional proprietary features that work only on Cisco products. In general, RIP works well in small environments, but has serious limitations when used in larger internetworks. For example, RIP limits the number of router hops between any two hosts in an internet to 16. RIP is also slow to converge, meaning that it takes a relatively long time for network changes to become known to all routers. RIP determines the best path through an internet by looking only at the number of hops between the two end nodes. This technique ignores other routing metrics, such as differences in line speed, line utilization, and other metrics, many of which can be important factors in choosing the best path between two nodes. See also Routing Protocol.

Rip Cord - An aid in stripping the jacket off of bundled pair cable. It is a nylon string that is put in telephone wire and cables when it is manufactured. The string is used by installers to rip the jacket or insulation when it is being installed.

RIR (Regional Internet Registry) - The regional organization responsible for assigning Internet Protocol (IP) addresses to either the National Internet Registry (NIR) or Local Internet Registries (LIRs) that, in turn, assign them to Internet Service Providers (ISPs). The RIR receives IP address assignments from the Internet Assigned Numbers Authority (IANA). RIRs include the following:

• African Network Information Center (AfriNIC)

• Asia Pacific Network Information Center (APNIC)

• American Registry for Internet Numbers (ARIN)

• Latin-American and Caribbean Network Information Center (LACNIC)

• Réseaux IP Européens Network Coordination Center (RIPE NCC)

In addition to general number administration, each RIR is responsible for maintaining one or more of the root servers, maintaining a Whois database for IP ownership lookups, deployment of a routing database, co-ordination of ENUM delegations, and network measurement and statistical reporting. See also ENUM, IANA, IP, IP address, ISP, LIR, NIR, and Whois.

rise and fall time - See cycle time.

Riser Cable - A twisted-pair cable (usually several hundred pairs) distribution system that progresses from the telephone company Demarc or point of entrance in a building to each floor of that building.

Riser - A telephone cable feed inside a building that runs vertically from floor to floor. It is called a riser because it is usually placed in a place that architects call risers. We call them elevator shafts, plenums, or airways, whichever the riser is used for. Typical copper pair riser cables are in the hundreds of pairs in size (100, 200, 300 pair, etc.).

Rivest-Shamir-Adleman (RSA) - See RSA.

RJ (Registration Jack) - The prefix to many telephone company connection and interface standards.

RJ11 - The telephone jack that most of us have come to know. It has a 6× plug with four conductors. Handset cords are a smaller plug, a 4× plug with four conductors. If you look at the two of them side by side, you will notice the difference.

RJ21 - Also known as RJ21X. See RJ21X.

RJ21X - An RJ21X is a 66M150 block that is designated as the demarcation point for telephone company-provided communications lines. Most RJ21X blocks have an orange cover where the telephone numbers of the lines are written.

RJ45 - An 8-position, 8-conductor modular jack. RJ45 is used in many computer LAN applications.

RJ48 - An 8-position, 8-conductor modular jack. Used to terminate T1 service.

RJ48X - An 8-position, 8-conductor modular jack. They are used to terminate T1 service and they have a shorting bar that is built-in for making manual loop-backs.

RM-Cell (Resource Management Cell) - In asynchronous transfer mode (ATM), a flow control feedback mechanism that communicates to the originating end-user device to change the transfer characteristics of the connection during periods of congestion.The network buffers cells and advises the sender to throttle back on the rate of transmission.The available bit rate (ABR) class of service makes use of RMCells.ABR is a best-effort category in which the network attempts to pass the maximum number of cells, but with no absolute guarantees. See also ABR, best effort, buffer, cell, congestion, and flow control.

RMA (Return Material Authorization) - See Return Material Authorization.

RMON (Remote Monitor) - A network management protocol that has an MIB (Management Information Base) extended beyond what SNMP (Simple Network-Management Protocol) provided. RMON enables a network manager to monitor, configure, and troubleshoot a network. RMON2 is a newer version of the original RMON that enables visibility for a system administrator to view the network and physical layers by protocol. See also SNMP.

RMS - See Root Mean Square.

road warrior - Someone who travels extensively on business, conducting business warfare on the road. The term originates in the Mel Gibson movie Mad Max 2:The Road Warrior (1981).

Roaming - When a cellular/PCS telephone travels outside of its calling area, it is roaming. When a cellular/PCS telephone roams, it continues to send a signal out that tells any cellular site it can reach (regardless of company) that “I am here.” If it can communicate with a cellular site, then the roam indicator is displayed on your phone. If you have a roaming service with your cellular/PCS company, then you can still receive calls even though you are out of your calling area. If you don’t pay extra for roaming service, you can still make outgoing calls; however, they cost extra.

Robbed-Bit Signaling - Also called bit robbing, but usually known as inband signaling. The practice of taking a bit here and there in the beginning and end of a digital transmission for use in the overhead of the transmission equipment. Bit robbing is bad news when the signals being multiplexed into the transmission are data. Robbing a bit from a data stream severely corrupts it. Bit robbing is reserved for multiplexing multiple voice circuits onto a T1. Circuits intended to transmit data use out-of-band signaling or clear-channel signaling.

Robust - A term that is synonymous with fast, flexible, and reliable.

Robustness Principle - Also known as Postel’s Law.A principle stated by Jon Postel in RFC 793 (1981) and again in RFC 1122 (1989), Requirements for Internet Hosts – Communications Layers.The Robustness Principle states,“Be liberal in what you accept, and conservative in what you send,” which essentially advises the Internet community to design host software in such a way as to 1) be prepared for malevolent incoming packets and 2) be prepared for deficiencies on other hosts that can make it unwise to exploit legal but obscure protocol features that can cause disruption if the other host misbehaves. See also host; Internet; packet; Postel, Jon; protocol; software; and standard.

ROH (Ringer Off Hook) - See Receiver Off Hook.

Rolm (Siemons-Rolm) - A telephone equipment manufacturer.

ROM (Read-Only Memory) - See Read-Only Memory.

Root Account - A type of log-on account that allows access to UNIX subsystems software used exclusively by network or system administrators. Root-account logins commonly give the user a “#” as a prompt, similar to the way that MS-DOS would give a C>. Programming changes are generally unrestricted when logged into a system as a root user. See also C Shell and V Shell.

Root Mean Square (RMS) - A method of calculating the power consumption or power output of an electronic/electrical device. RMS power is ultimately the average of an AC waveform, which is the peak voltage, multiplied by 0.707. The other methods of calculating power include true power, peak power, and transparent power. Most electronic/ audio applications use either peak or RMS power. To convert from peak power to RMS power, multiply the peak power rating by 0.707. The result is RMS power. To convert RMS power to peak power, divide the RMS power rating by 0.707. The result is the peak power rating.

root server - A server that serves as the central point in a hierarchical structure of database hosts. In the Internet, for example, root domain name servers (DNSs) are positioned as the authoritative sources of all domain names.The Regional Internet Registries (RIRs) maintain the root servers, to which they post domain names directly. Individual Internet service providers (ISPs) download updates from the root servers. See also database, DNS, Internet, RIR, and server.

root -1. In a hierarchically organized structure of entities, the main level from which all other levels branch out. Such a structure can take the form of a root with multiple branches, each of which may have multiple leaves. 2. In a hierarchical network tree topology, the central bus from which all other busses branch out. See also bus topology and tree topology. 3. In a hierarchically structured database, a record at the first level, from which all other records branch out. Such a structure is known as a tree.

Round-Trip Time (RTT) - The time (usually measured in milliseconds) 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. See also Network Transit Time Delay.

Route - Nortel’s name for a trunk group. See also Member.

Routed Protocol - A network communications language that is supported or “encapsulated and transmitted” by routers. Examples of routed protocols are Ethernet, Appletalk, TCP/IP, frame relay, and X.25. Routed protocols are encapsulated by routing protocols, such as Intermediate System to Intermediate System (IS-IS), Cisco System's Enhanced IGRP (Enhanced Interior Gateway Routing Protocol), and RIP (Routing Information Protocol). See also Routing Protocol.

Router - A network layer device that uses one or more measures (cost, number of hops, etc.) to determine the optimal path along which communications traffic should be forwarded. Routers forward packets from one network to another, based on address information. They are also capable of translating (or repackaging) data into dissimilar routed protocols, such as Ethernet, token ring, RS-232, etc. Routers were once called gateways. See also Routing Protocol.

routine' - Synonymous with procedure.A program module, or section of code, that executes a specific task.

Routing Domain - A group of routers and hosts operating under the same set of routing protocols. Within each routing domain is one or more areas. Each is uniquely identified by an area address.

Routing Information Protocol (RIP) - A traffic-control method used by routers. RIP was originally developed by Xerox Corporation in the early 1980s for use in Xerox Network Systems (XNS) networks. Cisco Systems has developed their own version of RIP that works well as a standard with other manufacturers’ routers and has additional proprietary features that work only on Cisco products. In general, RIP works well in small environments, but has serious limitations when used in larger internetworks. For example, RIP limits the number of router hops between any two hosts in an internet to 16. RIP is also slow to converge, meaning that it takes a relatively long time for network changes to become known to all routers. RIP determines the best path through an internet by looking only at the number of hops between the two end nodes. This technique ignores other routing metrics, such as differences in line speed, line utilization, and other metrics, many of which can be important factors in choosing the best path between two nodes. See also Routing Protocol.

Routing Metric (Routing Measure) - A 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, best packet size, path cost, and reliability.

Routing Protocol - The functional part of a router’s operating system that works with other routers within a network to transport data from one location to another. The three classes of routing protocols are: distance vector, link-state, and hybrid. Routing protocols work by incorporating algorithms that help the router know which port to relay data from and to. This is accomplished through routing tables that can be created statically (by a user) or dynamically (automatically by the routing protocol). Routing protocols carry data of other protocols (such as Ethernet, X.25, or TCP/IP) by placing an address in front of the packet to be routed. This address is translated by the routing protocol in routing tables to correspond to a MAC (Media-Access Control) address and/or a router port. Each time a packet passes through a router, the routing protocol header is read, stripped off, and a new header is added. Examples of routing protocols include Cisco System’s Enhanced IGRP (Enhanced Interior Gateway Routing Protocol), IS-IS (Intermediate System to Intermediate System), and RIP (Routing Information Protocol). See also Routed Protocol.

Routing Table - A reference to call-handling instructions input to an ACD (Automatic Call Distribution) system. The routing table lists each incoming trunk and the steps that the call goes through. The “steps” the call goes through are also called a “call treatment or a script.” A routing table could list trunk number 1 and the treatment that calls receive when they come in on that trunk. 2. An incoming digit translation file in a PBX system’s memory that instructs the system on which extension to route a call based on DNISI or D10 digits. 3. A list of paths or connections through a network that is kept in a router’s memory. See also OSPF. 4. A data file stored in a router or other internetworking device that keeps track of routes to particular network destination addresses and their associated circuit interface port on the router. Many routing protocols store metric data within routing tables as well. See also Routing Protocol and Routing Metric.

Routing - Referring to the process of deciding where to forward packets based on a view of the network as a whole. See also router.

RP - Redirecting Forward Party. Another name for a phone that is call forwarded.

RPELPC (Regular Pulse Excitation Linear Predictive Coding) - A speech encoding technique that uses regular pulses in an excitation frame and a long-term predictor, based on long-term correlation of voice samples, to model the speech pitch. RPELPC at 13 kbps is specified for use in cellular radio networks conforming to the pan-European GSM standard. See also cellular radio, encode, frame, and GSM.

RPR (Resilient Packet Ring) - The IEEE 802.17 specifications for a medium access control (MAC) layer protocol that uses Ethernet switching and a dual counter-rotating ring topology to optimize the transport of Ethernet/IP packet data traffic over optical fiber rings. RPR is designed to maintain the resiliency of SONET/SDH, but at a much reduced level of overhead.As RPR is independent of the Physical Layer, it can be implemented over existing SONET/SDH physical rings or can run on a standalone basis. RPR calls for dual counter-rotating local ringlets that interconnect nodes where data traffic is intended to drop. RPR also uses statistical multiplexing, which allows bandwidth to be oversubscribed, while establishing Committed Information Rate (CIR) and peak-rate thresholds per application. The nodes negotiate bandwidth requirements among themselves based on fairness algorithms and in consideration of a classification scheme that recognizes and provides higher priority access to traffic sensitive to latency and jitter while ensuring that best effort traffic, such as Internet traffic, is afforded equal access and a fair share of the remaining bandwidth. RPR supports the following class of service (CoS) levels:

• Class A traffic is intolerant of latency and jitter. RPR addresses Class A traffic through a high CIR that ensures the availability of an average level of bandwidth appropriate for high priority traffic such as real-time voice and video.

• Class B is more tolerant of latency and jitter. RPR addresses Class B traffic through either a lower CIR that ensures the availability of an average amount of bandwidth appropriate for medium priority applications that have less stringent QoS requirements, or through an Excess Information Rate (EIR) option. In the event of network congestion, Class B traffic is subject to fairness-based flow control. Class B is intended for business-class data traffic such as transaction processing.

• Class C traffic is best effort traffic with no latency or jitter requirements and, therefore, is strictly EIR traffic.

In the event of network congestion, Class B traffic is subject to fairness-based flow control. Class B traffic includes low priority applications such as consumer-level Internet access. In the event of a node or link failure, the RPR protection scheme can restore the network in 50 ms or less, which is the SONET/SDH benchmark.There are two restoral mechanisms: wrapping and steering.The wrap option calls for data to travel around the ring until it reaches the node nearest the break. That node turns the traffic around and sends it in the reverse direction over the counter-rotating ring.The steer option calls for the originating station to exercise sufficient intelligence to avoid the failed ring and place the traffic on the ring that retains continuity.Traffic continuously travels over both fibers of the dual counter-rotating ringlets. See also 802.17, bandwidth, best effort, CIR, CoS, EIR, Ethernet, flow control, IEEE, IP, jitter, latency, MAC, node, optical fiber, overhead, QoS, real-time, ring topology, SDH, SONET, and STDM.

RS-232 - A popular physical-layer interface now known as EIA/TIA-232. See EIA/TIA-232.

RS-232C - A communications protocol that was developed by the EIA so that data devices could communicate. The standard includes the different functions and signals for two devices to communicate. The signals are physically interfaced to a cable via a 25-pin or 9-pin connector. Each pin having a signal function. In order for an RS-232 connection to work, the cable and pin-outs must match. Even though most modem and DCE/DTE manufacturers use the RS-232 protocol, not all use the same pin-outs. To complete a connection, a cable must be a null cable (null-modem cable), which means that transmit and receive are reversed inside the cable from one end to the other.

RS-328 - The first EIA facsimile standard (1966).

RS-366 - EIA standard for auto-dialing.

RS-422 - Balanced electrical implementation of EIA/TIA-449 for highspeed data transmission. Now referred to collectively with RS-423 as EIA-530. See also EIA-530 and RS-423.

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.

RS-449 - 1. EIA standard that is the newer version of RS-232. RS-449 uses a 37-pin connector and each of multiple transmit and receive pairs are balanced. RS-449 is faster and able to transmit longer distances (300 feet) than RS-232 (limited to 50 feet). 2. Popular physical-layer interface. Now known as EIA/TIA-449. See EIA/TIA-449.

RS - 1. The ASCII control-code abbreviation for record separator. The binary code is 1110001 and the hex is E1. 2. RS Connectors, Recommended Standard, the prefix in RS-232, RS-328, etc.

RSA (Rivest-Shamir-Adleman) - A public key encryption algorithm developed by Ronald Rivest,Adi Shamir, and Leonard Adleman in 1978 that became a de facto standard. RSA formed the basis for a number of encryption programs, including Pretty Good Privacy (PGP). Current versions of RSA employ a 128-bit encryption algorithm, which is computationally infeasible to decode without the key.The 40-bit export version is not considered highly secure. See also encryption, PGP, public key encryption, and standard.

RSA (Rural Service Area) - The counterpart to MSA (Metropolitan Service Area). A term that refers to the 306 metropolitan areas where the FCC manages cellular and PCS communications. There are also RSA (Rural Statistical Area) markets that the FCC determined as separate from each other. 428 RSA markets are in the United States. Each statistical area, 734 in all, has at least two licensed service providers.

RSC (Remote Switching Center) - A common term for a long distance carrier’s central office, or relay point. Many Long Distance Carriers have offices that are not occupied by personnel, only equipment.

RSH - 1. Remote Shell. A UNIX operating system level of access. See also C Shell and Root. 2. Remote Shell Protocol. Referred to as R Shell from the similarities in the UNIX command set. An application or subprotocol that allows a user to execute commands on a remote system without having to log into the system. For example, rsh, along with a password (if the network OS supports passwords), can be used to remotely examine the status of network devices without connecting to each communication server, executing the command, and then disconnecting from the communication server.

RSS (Really Simple Syndication or Rich Site Summary) - A metadata push technology, i.e., a technology that can identify changes in data and initiate a content push to the end user, without the user having to search it out and pull it from the site.The term RSS is an umbrella term variously used to describe a number of versions of several data Web feed formats specified in Extensible Markup Language (XML) and used for syndication of Web content.Those standards include Really Simple Syndication, Rich Site Summary, and RDF Site Summary. More recently, the IETF adopted the Atom Publishing Protocol (APP), which builds on the previous RSS work.The Atom Syndication Format is described in IETF RFC 4287 (2005). See also metadata, push, We b, and XML.

RSVP (Resource ReserVation Protocol) - A transport-layer protocol that is intended to provide quality-of-service transmission levels in conjunction with TCP/IP over the Internet. The RSVP protocol makes the sender of data responsible for notifying the receiver that a call is to be made (or data to be sent) and what QOS (Quality of Service) will be needed. The responsibility of selecting the resources or path by which the transmission will take is given to the receiver or called party. RSVP is modeled to work with IPv6 and Ipv4.

rt (real-time) - Referring to a quality of service (QoS) level designed for applications that require transmission to take place in real time, that is to say that the transmission must take place at the exact moment and in the exact sequence as the event itself takes place in the real world. Real-time QoS is essential in many applications directly involving humans and their perception of time, and particularly those involving human-to-human interaction.Voice conversations and videoconferences take place in real time and demand real-time QoS. See also non-real-time, nrt, and QoS.

rt-VBR (real-time Variable Bit Rate) - In asynchronous transfer mode (ATM), a class of traffic that takes place in real time and that requires access to time slots at a rate that can vary significantly from time to time.Traffic parameters include peak cell rate (PCR), cell delay variation tolerance (CDVT), sustainable cell rate (SCR), maximum burst size (MBS), and burst tolerance (BT).The quality of service (QoS) parameter is cell loss ratio (CLR). Real-time compressed audio, voice, and video encoded at variable rates are examples of rt-VBR traffic.ATM also defines available bit rate (ABR), constant bit rate (CBR), non realtime Variable Bit Rate (nrt-VBR), unspecified bit rate (UBR), and variable bit rate (VBR) traffic classes. See also ABR, ATM, BT, CBR, CDVT, compression, MBS, nrt-VBR, PCR, QoS, real-time, SCR, time slot, UBR, and VBR.

RTCP (Real Time Control Protocol) - In the TCP/IP protocol suite, a companion protocol to the Real Time Transport Protocol (RTTP), RTCP allows monitoring of the data delivery in a manner scalable to large multicast networks, and provides minimal control and identification functionality. RTCP and RTP both are defined in IETF RFC 1889 (1996). See also IETF, multicast, protocol, protocol suite, RTP, and TCP/IP.

RTE (Registered Terminal Equipment) - See Registered Terminal Equipment.

RTF (Rich Text Formatting) - A standard developed by Microsoft Corporation for formatting text files in such a way that the formatting survives transfer not only between applications on a computer, but also between computers on a network. See also plain text and rich text.

RTM (Ready To Market) - A term indicating that a product has passed prescribed tests and is ready to go to market as a general release. Pre-release tests usually include an alpha test and a beta test.

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

RTP (Real Time Transport Protocol) - In the TCP/IP protocol suite, a mechanism for providing endto-end network transport functions suitable for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. Defined in IETF RFC 1889 (1996), RTP provides end-to-end delivery services including payload type identification, sequence numbering, and timestamping. In combination, the sequence numbering and timestamping provide the receiving node with sufficient information to resequence them as necessary. RTP does not address resource reservation and does not guarantee quality of service (QoS) for real-time services. RTP does not either guarantee delivery through the network or prevent out-of-order delivery, and it does not assume that the underlying network is reliable and delivers datagrams in sequence to the receiving machine. RTP does, however, prevent out-of-order delivery to the application.Applications such as voice over Internet Protocol (VoIP) generally run RTP on top of the User Datagram Protocol (UDP), which provides multiplexing and checksum services. In the context of the OSI Reference Model, RTP falls into both the Session Layer (Layer 5) and the Presentation Layer (Layer 6). RTP Control Protocol (RTCP) is an upper-layer companion protocol that allows monitoring of the data delivery. See also application, checksum, datagram, IETF, multicast, multiplex, payload, Presentation Layer, protocol, protocol suite, QoS, real-time, RTCP, Session Layer, TCP/IP, transport, UDP, unicast, and VoIP.

RTS (Request To Send) - 1. After a modem receives a CD (Carrier Detect) signal from another modem, the next step is to send some data. Before it sends data, it sends an RTS (Request To Send). After it receives a CTS (Clear To Send) from the far-end modem, it begins sending data.

RTSP (Real-Time Streaming Protocol) - An application-level protocol designed to utilize TCP/IP to enable real-time communications over the Internet, such as voice over IP.

RTT (Round Trip Time) - The time (usually measured in milliseconds) 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. See also Network Transit Time Delay.

rule of thumb - A rule, or guideline, based on experience and sound judgement rather than scientific knowledge.The origin of the term is vague, but some suggest that it originated in the practice of carpenters, seamstresses, artists, and other craftsmen of using their thumb to approximate measurements.The fact that the measurement of an inch is based on the distance between the thumbnail and the first joint certainly lends credence to this theory.

rules of engagement - Mutually agreed-upon rules that define how military forces should behave during times of war, including the treatment of prisoners and civilians. Rules of engagement differ from a warrior’s code, which is a less formal set of defined limits on what warriors can and cannot do if they want to continue to be regarded as warriors, rather than murderers or cowards. For the warrior who adheres to such an informal code or to the formal rules of engagement, certain actions are unthinkable, even in the most dire or extreme circumstances. Rules of engagement date at least to the Middle Ages in Europe, when highly trained and well-paid gentleman knights spent years in apprentice and training to prepare them to wage war.They wielded heavy weapons and they, and their steeds, wore heavy armor for protection against those same weapons wielded by their noble opponents in battles fought on the field of honor.The invention of the crossbow upset the balance, however, as one small bolt from a crossbow fired by even the least skilled, most common peasant farmer could topple even the mightiest and most gentlemanly knight wearing the heaviest armor. Once toppled to the ground, the knight became immobile and, therefore, an easy kill for a common peasant with a stiletto.This innovation was considered so disgraceful that Pope Innocent II in 1139 declared the crossbow “hateful to God and unfit for Christians.” The second Lateran Council of churches stated that, “We prohibit under anathema that murderous art of crossbowmen and archers, which is hateful to God, to be employed against Christians and Catholics from now on.” This decree did not prohibit the use of the crossbow against infidels, who apparently weren’t considered to be gentlemen, much less worthy of the protection of the Church.The Church of England also attempted to outlaw the crossbow. See also Geneva Convention and warrior’s code.

run-length encoding - A string coding compression technique used in facsimile machines to digitize and compress a document prior to transmission by identifying color redundancy in the original document. The transmitting machine scans a document from top-to-bottom and left-to-right, sensing dots of black and white, grayscale, or color at an interval that depends on the resolution setting. Rather than transmitting a set of bits identifying the value of each dot of each line, the scanning machine looks for redundancy, i.e., strings or runs, of dots of the same value.The machine then can transmit a set of bits identifying that value and the length of the run before the value changes. Modified Huffman (MH) is a run-length encoding compression technique used in Group III facsimile machines. See also compression, facsimile, Group III, MH, resolution, and string coding.

runt - An unintentionally truncated frame or packet.A runt is either malformed or errored in transit and must be ignored if received.

Rural and High Cost Program - In the United States, a program that subsidizes basic telephone service in high-cost areas of the United States and its territories.The Rural and High Cost Program is one of four programs established by the Telecommunications Act of 1996, supported by the Universal Service Fund (USF), and administered by the Universal Service Administrative Company (USAC). See also Telecommunications Act of 1996, USAC, and USF.

Rural Health Care Corporation (RHC) - See also RBOC and Rural Health Care Program.

Rural Health Care Program - In the United States, a program administered by the Rural Health Care Corporation (RHC) to subsidize telecommunications and Internet service for eligible rural health care providers in high-cost areas.The Rural Health Care Program is one of four programs established by the Telecommunications Act of 1996, supported by the Universal Service Fund (USF), and administered by the Universal Service Administrative Company (USAC). See also RBOC, Telecommunications Act of 1996, USAC, and USF.

RZ (Return to Zero) - A transmission format where each positive bit returns or drops to a zero value during its timing period. The drop-to-zero format assists in timing/synchronizing the transmission signal.

Sample Meridian 1 CCR Script
GOTO CLOSED IF LOGGED AGENTS QUEUE 1234=0
QUEUE TO 1234
GIVE RAN 105
GIVE MUSIC 100

SECTION LOOP
WAIT 60
GIVE RAN 106
GOTO DIFFICULTIES IF LOGGED AGENTS QUEUE 1234=0
GOTO LOOP

SECTION DIFFICULTIES
GIVE RAN 107
FORCE DISCONNECT

SECTION CLOSED
GIVE RAN 108
FORCE DISCONNECT

–RAN 105 Thank you for calling abc company, your call will be answered by the next available agent.
–RAN 106 Please continue to hold
–RAN 107 We are currently experiencing technical difficulties, please call alternate number xxx-xxxx
–RAN 108 We are closed, our business hours are . . . please call back during these times.

RFQ (Request For Quotation) See RFP.

routing by rumor - See distance-vector routing protocol.