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Telecommunications Dictionary

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D

data-grade cable- Cable that is capable of reliably transmitting digital data.

Data Link layer- Layer two of the OSI Reference Model. It controls the transfer of information between nodes over the Physical layer.

data- 1. A general term for information. 2. A collection of interrelated, unique data items or records, in one or more computer files.

data communications- The transmission and reception of data between locations. Data communications require a combination of hardware (terminals, modems, multiplexers, and other hardware) and software.

data integrity- A NOS function supporting error detection, correction, and data redundancy.

data rate- A measure of the signaling rate of a data link.

data stream- A Logical path between input and output devices and a host computer.

DB-9- A 9-pin connector used on token ring network adapters

DB-15- A 15-pin connector used on 10BASE-5 adapters. Also known as an AUI connector or DIX connector.

Demand Priority Access Method (DPAM)- The media access method used by 100VG-AnyLAN networks. A centrally controlled access method that uses repeaters to control transmission between end nodes.

destination address- The location to which a packet is sent.

Destination Service Access Point (DSAP)- An LLC field identifying the destination protocol.

Business Telephone Systems

dial-up- The use of a telephone to establish a connection.

digital- Data characters coded in discrete, separate pulses or signal levels.

Digital European Cordless Telecommunications (DECT)- An ETSI European wireless LAN standard.

dispersion- A fiber-optic transmission problem caused by the spreading of light pulses so that they become indistinguishable from each other.

Distributed Queue Dual Bus (DQDB)- The IEEE 802.6 MAN standard based on cell relay, which are the standard calls for a bandwidth of 2 x 45 Mbps today and a bandwidth of 2 x 150 Mbps in the near future.

distributed processing- Computers connected together by a communications network. Data processing occurs on each of the computers, unlike a centralized processing system in which terminals are connected to a host computer that performs all of the data processing.

distributed database- A client-server database.

distributed star topology- a physical topology in which several layers of hubs radiate or descend from each other.

DIX connector- See DB-15 .

DQDB- See Distributed Queue Dual Bus (DQDB).

driver- A small software program for operating a specific peripheral device such as a network adapter card or printer.

dual attachment concentrator (DAC)- An FDDI concentrator that is connected to both the primary and secondary rings.

dual attachment station (DAS)- An FDDI station that is connected to both the primary and secondary rings.

duplex- Transmission that permits simultaneous two-way communication. Synonymous with full duplex. See also half duplex and simplex.

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E

EIA/TIA- Electronic Industries Association/Telecommunications Industries Association

EIA/TIA-568- Commercial Building Telecommunications Wiring Standard of the EIA/TIA. Also known as the EIA/TIA SP-2840.

electromagnetic interference (EMI)- Electromagnetic radiation which disrupts the performance of another device.

EMI/RFI- Electromagnetic Interference/Radio Frequency Interference encapsulate- To add a header containing addressing and sequencing information to a data block so it can be transmitted correctly at a higher protocol level.

encrypt- To alter or encode data to prevent unauthorized access.

Ending Delimiter- Indicates the end of the frame.

end user- In a network, the person or program that is the ultimate source or destination of data.

enterprise network- A large internetwork typical of a large business enterprise.

Ethernet- A local area network (LAN) specification that uses baseband signaling at 10 Mbps, and uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Media Access Control (MAC) technique. The original Ethernet LAN is slightly different from the IEEE

802.3 standard. See Carrier Sense Multiple Access with Collision Detection

(CSMA/CD) . See also Media Access Control (MAC) .

European Telecommunications Standard Institute (ETSI)- A European standards organization involved with wireless LAN standards.

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F

FDDI - See Fiber Distributed Data Interface (FDDI) .

FDDI Follow-On LAN (FFOL)- A future extension of FDDI and FDDI-II technology being design to run at speeds of up to 2.4 Gbps. It should provide both packet and circuit-switching services, and interconnect a wide variety of wide area networking technologies including B-ISDN, SMDS, and ATM.

FDDI-II- A new FDDI standard based on a circuit-switching architecture, rather than a timed token passing scheme. Intended for isochronous voice, video, and multimedia applications, in addition to asynchronous data traffic.

Fiber Distributed Data Interface (FDDI)- The ANSI standard for highspeed transmission over fiber-optic cable.

fiber-optic cable- Thin, transparent fibers of glass or plastic that transmit data through pulses of light from a laser or light emitting diode (LED).

file transfer protocol (FTP)- A TCP/IP application used to send complete files with TCP/IP services.

filter- The process of separating the frames, packets, or frequencies of a communications channel to be forwarded from those to be discarded or removed.

flow control- The regulation of data transmission between two devices having different processing speeds to prevent loss of data when the slower device's receiving buffer fills up.

fragmentation- The process of breaking up data into appropriate sized units for transmission.

frame- A self-identifying group of bits. The first several bits are a header containing address and other control information, the next bits are the data being conveyed, and the last bits are a check sequence for error detection.

Frame Check Sequence (FCS)- A 16-bit field appended to the end of data link frames. The FCS determines if a frame was received without error.

Frame Control- Part of a token-ring or FDDI frame that indicates whether the frame is a MAC, LLC, or undefined frame.

Frame Status- Part of a token-ring or FDDI frame that indicates whether a ring station recognizes the destination address and copies the frame.

frequency- The number of times a periodic analog signal occurs within one second. Number is expressed in hertz (Hz).

full duplex- See duplex .

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G

gateway- a device that acts as an interface between two or more networks to connect dissimilar communications systems. A gateway translates from one set of protocols to another, at levels from the Physical layer (Level 1) up through the Application layer (Level 7) of the OSI Reference model.

Gbps- Gigabits per second.

Get- an SNMP message used to request information from a managed device.

gigabit- One billion bits of data.

group address- An address that includes a specified group of devices on the network. Only devices in this group simultaneously receive messages sent to this address.

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H

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half duplex- Transmission between two end points in either direction, but not in both directions simultaneously. See also duplex and simplex .

hard error- A type of serious error in a token ring network.

hardware- 1. Collectively, electronic circuit components and associated fittings and attachments. 2. In computer systems, the machinery associated with computation.

header- Coded information that precedes a data message and gives details about it, such as its destination address and length.

Hertz (Hz)- Transmission speed in cycles per second.

heterogeneous network- A data network comprised of devices from different manufacturers and/or different types of LANs.

high-level protocol- A protocol that allows network users to perform functions on blocks of data (such as formatting it) that are at a level higher than the Transport layer.

host computer- The main computer or large computer (mainframe) in a network.

hot swappable- A hub module which can be removed or inserted without LAN disruption.

hub- A multiport device which forms the central point of connectivity in a physical star topology. Also known as concentrator.

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I

impedance- The total opposition (a combination of resistance and reactance) offered by an electric circuit to the flow of an alternating current of a single frequency. The greater the impedance, the shorter the distance that the current can be sent down the wire. Impedance is measured in ohms.

input/output (I/O)- 1. The method, medium, or device (such as a keyboard, monitor, floppy disk, hard disk, network adapter, or printer) used to transfer data to a computing system or from the computing system to the outside world. 2. The interface between humans and a computer or between computers.

insertion loss- Attenuation caused by connections in the data path.

interface- 1. A physical device that connects two systems or two devices. 2. A standard (such as RS-232-C) that specifies how two systems can connect to each other.

International Standards Organization (ISO)- Developers of the Open System Interconnection (OSI) Reference Model that standardizes OSI protocols. See Open Systems Interconnection (OSI) Reference Model.

Internet Activities Board (IAB)- The group of researchers responsible for development of TCP/IP protocols for use by the Internet international network.

Internet Packet Exchange (IPX)- The routing protocol used by Novell NetWare.

Internet Protocol (IP)- The standard used in the context of the TCP/IP protocol suite for sending a basic unit of data, the IP datagram, through an internetwork. IP is the Network-layer protocol of the TCP/IP protocol suite.

Internet- A large international network that includes the Advanced Research Projects Agency Network (ARPANET), the Military Network (MILnet), and the National Sciences Foundation Network (NSFnet).

internetwork- Two or more networks that can pass data and share resources as if they were a single network.

isochronous transmission- A transmission service allowing the sending and receiving of data in equal time increments. Most often used for time-sensitive transmission of voice and video traffic.

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