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| Tecnología |
| Glosario de Términos de Telecomunicaciones |
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Analog Data: Data represented by a physical quantity that is considered to be continuously variable and whose magnitude is made directly proportional to the data or to a suitable function of the data. Analog Signal: A continuously varying electromagnetic wave that may be propagated over a variety of media. Analog Transmission: The transmission of analog signals without regard to content. The signal may be amplified, but there is no intermediate attempt to recover the data from the signal. Application Layer: Layer 7 of the OSI model. This layer determines the interface of the system with the user and provides useful application-oriented services. Asynchronous Transfer Mode (ATM): A form of packet switching in which fixed-size cells of 53 octets are used. There is no network layer and many of the basic functions have been streamlined or eliminated to provide for greater throughput. Asynchronous Transmission: Transmission in which each information character is individually synchronized, usually by the use of start elements and stop elements. Automatic Repeat Request (ARQ): A feature that automatically initiates a request for retransmission when an error in transmission is detected. Beamwidth: The angular width of the main lobe of an antenna radiation pattern as measured between predetermined points on the lobe, usually the half-power (-3 dB) points. Baseband: Transmission of signals without modulation. In a baseband local-area network, digital signals (1's and 0's) are inserted directly onto the cable as voltage pulses. The entire spectrum of the cable is consumed by the signal. This scheme does not allow frequency-division multiplexing. Baud: A unit of signaling speed denoting the number of discrete signal elements that can be transmitted per second. The word baud is derived from the name of J.M.E. Baudot (1845-1903), a French pioneer in the field of printing telegraphy and the inventor of Baudot code. Although technically inaccurate, baud rate commonly is used to mean bit rate. Because each signal element or baud may translate into many individual bits, bits per second (bps) normally differs from baud rate. Baudot code: A 5-bit code used in many types of data communications, including Teletype (TTY), radio Teletype (RTTY), and telecommunications devices for the deaf (TDD). Baudot code has been revised and extended several times. Bridge: An internetworking device that connects two similar local-area networks that use the same LAN protocols. Broadband: In local-area networks, the use of coaxial cable for providing data transfers by means of analog (radio frequency) signals. Digital signals are passed through a modem and transmitted over one of the frequency bands of the cable. Broadband ISDN (BISDN) : A second-generation set of standards for ISDN. BISDN is characterized by the use of asynchronous transfer mode and by the provision of very high data rates to end-users. Bus: A LAN topology in which stations are attached to a shared transmission medium. The medium is a linear cable; transmissions propagate the length of the medium and are received by all stations. Circular Polarization: A special method of radio energy emission where the electric and magnetic field vectors rotate about the central axis of radiation. As viewed along the radiation path, the rotation directions are considered to be right-ha nd-circular(RHCP) if the rotation is clockwise and left-hand-circular(LHCP) if the rotation is counterclockwise. Centrex: A service offered by operating telephone companies that provides, from the telephone company office, functions and features comparable to those provided by a PBX. Ciphertext: The output of an encryption algorithm; the encrypted form of a message or data. Circuit Switching: A method of communication in which a dedicated communications path is established between two devices through one or more intermediate switching nodes. Unlike with packet switching, digital data are sent as a continuous stream of bits. Data rate is guaranteed, and delay is essentially limited to propagation time. Codec (Coder-decoder) : Transforms analog data into a digital bit stream (coder) and digital signals into analog data (decoder). Common-Channel Signaling: Technique in which network control signals (e.g., call request) are separated from the associated voice or data path by placing the signaling from a group of voice or data paths on a separate channel dedicated to signaling only. Communications Architecture: The hardware and software structure that implements the communications function. Conventional Encryption: A form of cryptosystem in which encryption and decryption are performed using the same key. CSMA/CD: Carrier sense multiple access with collision detection. A medium access control technique for bus and tree LANs. A station wishing to transmit first senses the medium and transmits only if the medium is idle. The station ceases transmission if it detects a collision. Cyclic Redundancy Check (CRC): An error-detecting code in which the code is the remainder resulting from dividing the bits to be checked by a predetermined binary number. Data Circuit-Terminating Equipment (DCE) : In a data station, the equipment that provides the signal conversation and coding between the data terminal equipment (DTE) and the line. The DCE may be separate equipment or an integral part of the DTE or of intermediate equipment. The DCE may perform other functions that are normally performed at the network end of the line. Data Compression: The process of eliminating gaps, empty fields, redundancies, and unnecessary data to shorten the length of records or blocks. Datagram: In packet switching, a self-contained packet, independent of other packets, that carries information sufficient for routing from the originating data terminal equipment (DTE) to the destination DTE without relying on earlier exchanges between the DTEs and the network. Data Link Layer: Layer 2 of the OSI model. Converts an unreliable transmission channel into a reliable one. Data Terminal Equipment (DTE) : Equipment consisting of digital end instruments that convert the user information into data signals for transmission or reconvert the received data signals into user information. Digital Data: Data represented by discrete values or conditions. Digital Data Switch: A local network consisting of a central switch that uses circuit switching. Digital PBX: A private branch exchange (PBX) that operates internally on digital signal. Thus, voice signals must be digitized for use in the PBX. Digital Signal: A discrete or discontinuous signal, such as a sequence of voltage pulses. Digital Signature: An authentication mechanism that enables the creator of a message to attach a code that acts as a signature. The signature guarantees the source and integrity of the message. Digital Transmission: The transmission of digital data or analog data that have been digitized, using either an analog or digital signal, in which the digital content is recovered and repeated at intermediate points to reduce the effects of impairments, such as noise, distortion, and attenuation. Digitize: To convert an analog signal to a digital signal. Direct Inward Dialing: A service feature that allows inward-directed calls to a PBX to reach a specific PBX station without attendant assistance. Distributed Data Processing: Data processing in which some or all of the processing, storage, and control functions, in addition to input-output functions, are dispersed among data processing stations. Elliptical Orbit: Those orbits in which the satellite path describes an ellipse with the Earth at one focus. Elevation: The angle above the local horizontal plane, usually specified in degrees. (0 degrees = plane of the Earth's surface at your location; 90 degrees = straight up, perpendicular to the plane of the Earth). Epoch: The reference time at which a particular set of parameters describing satellite motion (Keplerian elements) are defined. Electronic Data Interchange: The direct computer-to-computer exchange of information normally provided on standard business documents, such as invoices, bills of lading, and purchase orders. Encapsulation: The addition of control information by a protocol entity to data obtained from a protocol user. Encryption: To convert plain text or data into unintelligible form by means of a reversible mathematical computation. Error-Detecting Code: A code in which each data signal conforms to specific rules of construction, so that departures from this construction in the received signal can be detected automatically. Error Rate: The ratio of the number of data units in error to the total number of data units. Ethernet: A 10-Mbps baseband local-area network specification developed jointly by Xerox, Intel, and Digital Equipment. It is the forerunner of the IEEE 802.3 CSMA/CD standard. Frequency Division Multiple Access (FDMA): Multiple access being achieved through frequency band discrimination; either in the ground receiver, in the case of a wide band frequency translating repeater, or in the satellite, in the case of a frequ ency channelized satellite. Fiber Distributed Data Interface (FDDI): A standard for a 100-Mbps optical fiber ring local-area network. Flow Control: A function performed by a receiving entity to limit the amount or rate of data sent by a transmitting entity. Frame Check Sequence: An error-detecting code inserted as a field in a block of data to be transmitted. The code serves to check for errors upon reception of the data. Frame Relay: A form of packet switching based on the use of variable-length link layer frames. There is no network layer, and many of the basic functions have been streamlined or eliminated to provide for greater throughput. Frequency-Division Multiplexing (FDM): Division of a transmission facility into two or more channels by splitting the frequency band transmitted by the facility into narrower bands, each of which is used to constitute a distinct channel. Full-Duplex Transmission: Transmission of data in both directions at the same time. Continuará..... Regresar A: Tecnología | Página de Inicio
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