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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