Glossary H-I

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  • H: Symbol designation for magnetic intensity & henry. Also See Henry
  • Half Duplex: (HDX) Transmission in either direction at a time; i.e. the two communication DTE's cannot transmit simultaneously.
  • Handshaking: Exchange of predetermined signals between two devices establishing a connection. Usually part of a communications protocol.
  • Hardware: Physical equipment (as opposed to "software" or the computer programs)
  • Harness: An arrangement of wires & cables usually with many breakouts, which have been tied together or pulled into a rubber or plastic sheath, used to interconnect an electrical circuit.
  • HDLC: See High-level Data Link Control
  • HDMI: See High-Definition Multimedia Interface
  • HDTV: See High-Definition Television
  • HDX: See Half Duplex
  • Head End: A passive component in broadband transmission networks that translates 1 range of frequencies (transmit) to a different frequency band (receive); allows devices on a single cable network to send & receive signals without interference.
  • Header: Auxiliary information preceding a transmission block.
  • Headroom: The amount by which a cable ACR exceeds 10 dB. The TIA/EIA 568B Standard states a minimum of 10 dB of ACR is required for Category 5 certification.
  • Heartbeat: Ethernet defined SQE signal quality test function.
  • Height Level Language Applications Programming Interface: (HLLAPI) An IBM API.
  • Helical Scan: Storage method that increases media capacity by laying data out in diagonal strips.
  • Henry: (H) A practical unit of inductance that will produce a voltage drop of one volt when the current changes at the rate of one ampere per second.
  • Hertz: (Hz) A term replacing cycles per second for frequency. It distinguishes electromagnetic waveform energy; number of cycles, or complete waves that pass a reference point per second, measurement of frequency by which one Hertz equals 1 cycle per second.
  • Heterogeneous Networks: Networks composed of hardware & software from multiple vendors usually implementing multiple protocols.
  • Hierarchical Backbone: A backbone with more than one layer in the overall network architecture. Each layer can be either distributed or collapsed.
  • High-Definition Multimedia Interface: (HDMI) An interface used for High Definition TV. Typically connects from video sources like DVD players or Blue-Ray players to display screens. Digital audio is included in the HDMI interface.
  • High-Definition Television: (HDTV) Higher resolution TV, typically 1080 horizontal lines. Substantially higher than NTSC or PAL television. Typically transmitted as digital.
  • High-level Data Link Control: (HDLC) An ISO protocol for X.25 international communications.
  • HLLAPI: See Height Level Language Applications Programming Interface
  • Home Page: Also knows as Web Page or Web Site. Conveys information with graphic, text & now multimedia Capabilities. Usually the page named "index.html"
  • Home-Run Cabling: A distribution method in which single cables are run directly from the horizontal cross-connect to each telecommunications outlet. This is also known as star topology.
  • Hop Count: A field in the header of OP packet which counts the number of routers through which the packet has been forwarded. When hop count reaches a specified maximum value, the packet is discarded.
  • Horizontal Cabling: The wiring/cabling between the telecommunications outlet/connector & the horizontal cross-connect.
  • Host: A computer attached to a network. It typically refers to a multi-user computer but may be any addressable node on a LAN.
  • Host Computer: The primary controlling computer in a multiple computer system. the term is normally used for relatively more powerful or large computers.
  • Hot Swappable: The process or replacing a module or subassembly component in an electronic device without requiring a power off situation to occur.
  • HTML: See Hypertext Markup Language
  • HTTP: See Hyper-Text Transport Protocol
  • Hub: The communications center of a network or cabling system. Star topology
  • HUM: A term used to describe the 60- or 120 cycle per second noise present in the sound of some communications equipment. Usually hum is the result of undesired coupling to a 60 cycle source or to the defective filtering of 120 cycle ripple output of a rectifier.
  • Hyper-Text Transport Protocol: (HTTP) The Method of transferring web page data over the internet.
  • Hypermedia: The Combination of hypertext & multimedia in an online document.
  • Hypertext: A type of text that allows embedded "links" to other documents. Clicking on or selecting a hypertext link displays another document or section of a document. Most World Wide Web documents contain hypertext.
  • Hypertext Markup Language: (HTML) a tagging language used to create web pages used on the World Wide Web.
  • HZ: See Hertz
  • I: A symbol used to designate current.
  • I/O address: See Input/Output Address
  • IANA: See Internet Assigned Numbers Authority
  • ICEA: Insulated Cable Engineers Association.
  • ICMP: See Internet Control Message Protocol
  • Icon: A graphic symbol.
  • IEC: See Innovative Electronics & Computing
  • IEEE: See Institute of Electrical & Electronic Engineers
  • IEEE 802.3: The physical layer standard specifying a LAN with a CSMA/CD access method on a bus topology (e.g. Ethernet).
  • IEEE 802.4: The physical layer standard specifying a LAN with a token passing method on a bus topology (e.g. MAP).
  • IEEE 802.5: The physical layer standard for a LAN with a token passing access method using a ring topology.
  • IF: See Intermediate Frequency
  • Impedance: The total opposition a circuit offers to the flow of an alternating current at a particular frequency. A combination of D.C. resistance & reactance, or in other words, the friction or back pressure. Impedance is measured in ohms. Consistency is met when speed (frequency) increases.
  • Impedance Match: A condition whereby the impedance of a particular circuit cable or component is the same as the impedance of the circuit, cable, or devices to which it is connected.
  • Impedance Matching Transformer: A transformer designed to match the impedance of one circuit to that of another
  • Impulse Noise: Pulse or pulses appearing at the output point of a data link, which were not transmitted at the input point. Impulse noises are usually caused by external electrical sources, such as lighting.
  • Index of Refraction: The ratio of light velocity in a vacuum to its velocity in a given transmitting medium.
  • Inductance: A property of a conductor or circuit which resists a change in current. It causes current changes to lag behind voltage changes & is measured in henrys.
  • Induction: The phenomenon of a voltage, magnetic field, or electrostatic charge being produced in an object by line of force from the source of such fields.
  • Industry Standard Architecture: (ISA) The popular architecture for 1980s and early 1990s personal computer buses, such as the IBM PC,XT, & AT.
  • Information Transfer: Synonymous with data transfer. Information is a broader term than data. Information includes: voice, graphics, & other types of signals.
  • Initial Handshaking: A commonly used term for a sequence in data transfer. During initial handshaking, the two communicating DTE's may exchange identities & confirm that they can transfer data.
  • Innovative Electronics & Computing: (IEC) . Answering all of your Interface Questions and Cable needs. IEC has a full line of Cable Assemblies, Switches, Networking Equipment, Tools & Test Equipment & so much more.
  • Input: A signal (or power) which is applied to a piece of electric apparatus or the terminals on the apparatus to which a signal or power is applied.
  • Input-Output Controller: (IOC) A sub-unit in a computer or attached to a computer that manages the movement of data between the computer & the input & output devices (I/O devices), such as, keyboards, video display units & printers.
  • Input-Output Program: A program that manages the movement of data between the computer & the input & output devices (I/O devices).
  • Input/Output Address: (I/O address) Starting address for data input & output.
  • Insertion Loss: The loss caused by the inclusion of a splice, connector or other such component in a system.
  • Inside Wiring: In telephone deregulation, the customer's premises wiring; the wiring inside of a building.
  • Institiute of Electrical & Electronic Engineers: (IEEE) A standards making organization.
  • Insulation: A material having good dielectric properties which is used to separate close electrical components such as cable conductors & circuit components.
  • Integrated Service Unit: (ISU) A single device that combines the functions of both a CSU & a DSU.
  • Integrated Services Digital Network: (ISDN) The ideas behind the need for an ISDN is that there are growing consumer requirements for digital services over long distances, demands placed on the telephone network.
  • Inter-Character Gap: During asynchronous start-stop transmission, the interval of time between the stop bit of one character & the start bit of the next character.
  • Interactive Processing: Describing time-dependent (real-time) data communications; a user enters data & waits for response from the destination before continuing; also, conversational; contrast with batch processing.
  • Interchange Code: A set of unambiguous rules specifying the way in which data may be represented.
  • Interconnect: Provides for the direct connection of individual cables to another cable or to an equipment cable without a patch cord.
  • Interface: The boundary between hardware & software components of a network.
  • Interference: Disturbances of an electrical or electromagnetic nature that introduce undesirable responses into other electronic equipment.
  • Intermediate Frequency: A frequency to which signal is converted for ease of handling. Receives its name from the fact that it is an intermediate step between the initial & final conversion or detecting stages.
  • International Standard: An ISO standards document that has been approved in final balloting.
  • International Standards Organization: (ISO) An organization of 89 member countries (founded in 1946) responsible for setting world standards in many electronics areas. Members of the ISO are the national standards organizations of the member countries.
  • International Telegraphic Union - Telecommunications Standards Sector: (ITU-TSS) The replacement organization for the CCITT.
  • Internet: Made up of millions of smaller connected networks. It is the largest computer network. Founded by the United States Department of Defense. It was created for a fail safe computer system in case of a nuclear attack.
  • Internet Address: (IP Address) This is a 32 bit hardware independent address assigned to hosts using the TCP/IP: protocol suite.
  • Internet Assigned Numbers Authority: (IANA) The central registry for various Internet protocol parameters, such as port, protocol & ent4erprise numbers, & options, codes & types.
  • Internet Control Message Protocol: (ICMP) A part of IP that handles error & control messages. It is used by gateways & hosts to report problems with the datagram to the original source. ICMP also has an echo request/reply feature used to test whether a node is alive or dead.
  • Internet Protocol: (IP) TCP/IP protocol governing packet forwarding.
  • Internet Relay Chat: (IRC) a means of communicating with others over the internet, in Real Time via Text messages.
  • Internet Service Provider: (ISP) A company that maintains a network that is linked to the internet via a dedicated communication line, usually a high-speed link known as a T1. An ISP offers use of its dedicated communication lines to companies & individuals. Using a modem, you can dial up to a service provider whose computers will connect you to the Internet.
  • Internet Society: (ISOC) A non-profit, professional organization that supports the technical evolution of the Internet & stimulates the interest of members of the scientific & academic communities, industry, & the public regarding technology & the applications of the Internet.
  • Internetwork: The ability to operate & exchange information in a heterogeneous network.
  • Internetwork Packet Exchange: (IPX) NetWare protocol similar to IP.
  • Internetworking: The use of linking devices such as gateways, bridges & routers to connect network systems of same or varied configurations.
  • Interoperability: The ability of two computers to communicate & exchange information with each other.
  • Interprocess Communications: (IPC) A protocol for data exchange between applications or threads.
  • Interrupt Request: (IRQ) The method by which hardware devices request processor attention.
  • Inverted Backbone: A distributed backbone in which a LAN is used for the backbone but it is physically contained in a small area, , i.e. an equipment room. This is usually found in token ring environments where 2 port bridges are connected to a 16MB backbone ring in the computer room.
  • IOC: See Input-Output Controller
  • IP: See Internet Protocol
  • IP Address: See Internet Address
  • IPC: See Interprocess Communications
  • IPX: See Internetwork Packet Exchange
  • IRC: See Internet Relay Chat
  • IRQ: See Interrupt Request
  • IRS: Ignition radiation suppression.
  • ISA: See Industry Standard Architecture
  • ISDN: See Integrated Services Digital Network
  • ISO: See International Standards Organization
  • ISOC: See Internet Society
  • Isolation: The ability of a circuit or component to reject interference, usually expressed in dB.
  • ISP: See Internet Service Provider
  • ISU: See Integrated Service Unit
  • ITU-TSS: See International Telegraphic Union - Telecommunications Standards Sector The replacement organization for the CCITT.
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