0-9  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z radio frequency (RF) Electromagnetic waves propagating in free space without a copper or fiber guide. A frequency band that is higher than the audio frequencies but below the infrared frequencies. rain fade The temporary loss of a wireless signal due to the inability of the signal to penetrate unusually heavy rain clouds or rainfall. Rain fade is usually brief, lasting only as long as the heavy rain-cloud condition persists. Raman amplifier A device that uses a pump laser to strengthen an optical signal by using the optical fiber as the amplification medium. This contrasts with an erbium-doped fiber amplifier (EDFA), which uses a piece of fiber doped with the element erbium to amplify the optical signal. Raman pump module If a beam of light is sufficiently intense and monochromatic, a threshold can be reached beyond which light at the Raman frequencies is amplified and which exhibits the characteristics of stimulated emission. Raman lasers use cladding pumped fiber technology, which differs from erbium doped fiber amplifiers (EDFAs), allowing higher power for longer transmission distances or higher data rates. Rayleigh scattering Scattering of light from inhomogeneities of material density or composition. In fiber optics, one of the causes of attenuation. receive power The measured power of the received signal strength. The receive power is the decibel ratio of Watts to one milliwatt (dBm). In other words, the output power of a signal referenced to an input signal of one milliwatt. receiver A device that detects an optical signal and converts it into electrical form usable by other devices. A receiver transforms an optical signal into an electrical signal. Receivers include preamplifiers, bandpass filters, photodetectors, and electronic detectors. recurring revenue Refers to sources of revenue that occur predictably at regular, typically monthly periods, on an ongoing basis. Examples include license fees, contractual obligations, rents, and ongoing maintenance fees. Generally, investors like recurring revenues because they are typically stable and predictable. refraction The bending of light as it passes between materials of a different refractive index. refractive index The refractive index of a material is the ratio of the speed of light in a vacuum to the speed of light in that material. regenerator A receiver-and-transmittor combination used to reconstruct signals for digital transmission. In an optical regenerator, the receiver converts incoming optical pulses to electrical pulses, decides whether the pulses are 1s or 0s, generates "cleaned-up" electrical pulses, and then converts them to squared-off pulses for transmission. regional Bell operating company (RBOC) An ILEC created by AT&T's divestiture of its local exchange business. The remaining RBOCs are BellSouth, Bell Atlantic, US WEST, and SBC Communications. relational database management system (RDBMS) A collection of programs that enables one to store, modify, and extract information from a database using a flexible retrieval process based on an infinite combination of relationships among stored data. remote access A workstation-to-network connection made using a modem and a telephone line that allows data to be sent or received over greater distances than those allowed by conventional cabling request for quote (RFQ) A document submitted by the customer and delivered to the vendor that requests a price for hardware, software or services to solve a specific problem. research and development (R&D)   restoration With protection, one of the main methods used to ensure the survivability of optical networks. Restoration uses any available capacity between nodes to transport data to replace a failed link. Restoration options include centralized or distributed architectures and either dynamic or preplanned routing strategies. Restoration takes longer than protection but is more efficient in its use of available capacity. return on assets (ROA) A measure of a company's profitability that is equal to the company's earnings, usually for the fiscal year, divided by its total assets, expressed as a percentage. return on equity (ROE) This figure indicates the performance of the stockholder's investment in the company. The relative performance of the investment can be gauged by comparing trends over time as well as comparisons to other firms in the industry. The figure, generally stated as a percentage, is equal to net income for a given period of time, usually the fiscal year, (after preferred stock dividends but before common stock dividends) divided by the company's stockholder's equity. return on investment (ROI) ROI is a measure of a corporation's profitability, equal to a fiscal year's income divided by common stock and preferred stock equity plus long-term debt. ROI is also used to quantify or describe income generated or costs reduced by capital investments made by a firm. revenue multiples Revenue multiples are often used to value companies with negative operating cash flows, and are a common measure for new technology companies. Multiples for any given company are compared to the multiples for the comparable companies to help assess whether a company is under- or over-valued. Calculated as enterprise valuation divided by forward revenues. revenue per user (RPU) The average revenue a company generates on a per customer or per unit basis over a stated period of time. RPU is usually reported in terms of dollars per month. ring Connection of two or more stations in a circular logical topology. Information is passed sequentially between active stations, each one in turn examining or copying the data and finally returning it to the originating station, which removes it from the network. ring topology Topology in which the network consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop. Each station on the network connects to the network at a repeater. Rivest-Shamir-Adleman (RSA) A highly secure cryptography method by RSA Data Security, Inc. that uses a two-part key to control access to websites and data. The private key is kept by the owner; the public key is published. Data is encrypted by using the recipient's public key, which can only be decrypted by the recipient's private key. RSA is also used for authentication by creating a digital signature. In this case, the sender's private key is used for encryption, and the sender's public key is used for decryption. route mile The length of cable laid, irrespective of the number of strands of fiber per cable. router A combination of hardware and software that connects and manages the flow of information between different types of networks (connecting two or more networks of differing protocols). A router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks to which it is connected. A router is located at any juncture of networks, or gateway, including each Internet point of presence. A router is often included as part of a network switch. routing The process of determining the path information takes when moving through a switched network.