Glossary H-I0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
- H: Symbol designation for
magnetic intensity & henry. Also See Henry
Duplex: (HDX) Transmission in either direction at a time; i.e. the two
communication DTE's cannot transmit simultaneously.
Exchange of predetermined signals between two devices establishing a
connection. Usually part of a communications protocol.
Physical equipment (as opposed to "software" or the computer
- 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.
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
- Heartbeat: Ethernet defined SQE signal quality test
- Height Level Language Applications
Programming Interface: (HLLAPI) An IBM API.
- Helical Scan: Storage method that
increases media capacity by laying data out in diagonal
- 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
- 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
- Heterogeneous Networks: Networks composed of hardware &
software from multiple vendors usually implementing multiple
- Hierarchical Backbone: A backbone with more than one layer
in the overall network architecture. Each layer can be either distributed or
- 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.
Television: (HDTV) Higher resolution TV, typically 1080 horizontal lines.
Substantially higher than NTSC or PAL television. Typically transmitted as
- High-level Data Link Control: (HDLC) An
ISO protocol for X.25 international communications.
- HLLAPI: See Height Level Language Applications Programming
- Home Page: Also knows as Web Page or Web Site. Conveys
information with graphic, text & now multimedia Capabilities. Usually the page
- 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.
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
- Host: A computer attached to a network. It
typically refers to a multi-user computer but may be any addressable node on a
- Host Computer: The primary controlling computer in a multiple
computer system. the term is normally used for relatively more powerful or
- 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
- HTTP: See Hyper-Text Transport
- 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
- 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 Markup Language: (HTML) a
tagging language used to create web pages used on the World Wide
- HZ: See Hertz
- I: A symbol used to
- I/O address: See Input/Output
- IANA: See Internet Assigned Numbers
- ICEA: Insulated Cable Engineers
- ICMP: See Internet Control Message
- Icon: A graphic symbol.
- IEC: See Innovative Electronics & Computing
- IEEE: See Institute of Electrical & Electronic Engineers
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
- 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
- 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
- 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.
Standard Architecture: (ISA) The popular architecture for 1980s and early
1990s personal computer buses, such as the IBM PC,XT, & AT.
Transfer: Synonymous with data transfer. Information is a broader term than
data. Information includes: voice, graphics, & other types of
- 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
- 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
- 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).
Address: (I/O address) Starting address for data input &
- 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
- 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
- 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.
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.
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
- International Standard: An ISO standards document that has
been approved in final balloting.
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
- 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 &
- 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
- 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
- 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 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
- Internetwork: The ability to operate & exchange information
in a heterogeneous network.
- Internetwork Packet
Exchange: (IPX) NetWare protocol similar to IP.
The use of linking devices such as gateways, bridges & routers to connect
network systems of same or varied configurations.
The ability of two computers to communicate & exchange information with each
- 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
- IOC: See Input-Output
- IP: See Internet Protocol
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
- ISA: See Industry Standard
- ISDN: See Integrated Services
- ISO: See International Standards
- ISOC: See Internet
- 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.