Telecom Dictionary - Definitions of terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

I

I2 - Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by government researchers and academic institutions.

IAL - Abbreviation for Immediate Action Limit. The bound on performance allowed for a circuit or connection that is in service. When any parameter value exceeds the IAL, the circuit or connection is considered defective and corrective action is necessary.

IANA - Abbreviation for Internet Assigned Numbers Authority. An organization directed by the Internet Architecture Board (IAB) and which assigns IP numbers and protocol parameters such as port, protocol, and enterprise numbers, and options, codes, and types.

I_a - The 4-wire (2-pair) bidirectional primary rate interface point on the network side of the termination equipment (i.e., NT1, NT2), including the equipment connecting cord, or equivalent, on the user side of the interface cable.

I_b - The 4-wire (2-pair) bidirectional primary rate (PR) interface point on the user side of the termination equipment (i.e., NT1 and NT2), including the equipment connecting cord or equivalent on the network side of the interface cable.

IC - Abbreviation for integrated circuit (IC): An electronic circuit that consists of many individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other active and passive semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of substrate material. Synonyms chip, microcircuit.

ICA - Abbreviation for International Communications Association.

ICI - Abbreviation for incoming call identification. A switching system feature that allows an attendant to identify visually the type of service or trunk group associated with a call directed to the attendant's position.

ICMP - Abbreviation for Internet Control Message Protocol. An Internet protocol that reports datagram delivery errors. Note 1: ICMP is a key part of the TCP/IP protocol suite. Note 2: The packet internet gopher (ping) application is based on ICMP.

Icon - In computer systems, a small, pictorial representation of an application software package, idea, or concept used in a window or a menu to represent commands, files, or options.

ICW - Abbreviation for interrupted continuous wave. Modulation in which there is on-off keying of a continuous wave.

Identification - [The] process an information system (IS) uses to recognize an entity.

Identification, Friend or Foe (IFF) - A system using electromagnetic transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. Note: The secondary surveillance radar (SSR) system used in modern air traffic control systems is an outgrowth of the military IFF system used during World War II. The IFF equipment carried by modern military aircraft is compatible with the transponder system used for civilian air traffic control.

Identification Friend or Foe Personal Identifier - The discrete identification, friend or foe code assigned to a particular aircraft, ship, or other vehicle for identification by electronic means.

Identification Information -A form of notification information that consists of the documentation of the actual sequence of intermediate networks traversed by a signaling message. The documentation of the sequence of networks traversed may also include the origination and destination networks. The documentation that the message traversed a given network is performed by that network itself. Intermediate networks that are not ISNI-capable are not identified. ISNI identification information can be used to force a return error message, destined for the originating SEP, to transit the same intermediate network(s) as the original message.

Identifier (ID) - 1. In telecommunications and data processing systems, one or more characters used to identify, name, or characterize the nature, properties, or contents of a set of data elements. 2. A string of bits or characters that names an entity, such as a program, device, or system, in order that other entities can call that entity. 3. In programming languages, a lexical unit that names a language object, such as a variable, array, record, label, or procedure. Note: An identifier is placed in a label. The label is attached to, is a part of, or remains associated with, the information it identifies. If the label becomes disassociated from the information it identifies, the information may not be accessible.

Identity Authentication - The performance of tests to enable a data processing system to recognize entities. Note: An example of identity authentication is the checking of a password or identity token.

Identity Token - 1. A device, such as a metal key or smart card, used for identity authentication.2. [A] Smart card, metal key, or other physical object used to authenticate identity.

Identity Validation - Tests enabling an information system to authenticate users or resources.

IDF - Abbreviation for intermediate distribution frame. In a central office or customer premises, a frame that (a) cross-connects the user cable media to individual user line circuits and (b) may serve as a distribution point for multipair cables from the main distribution frame (MDF) or combined distribution frame (CDF) to individual cables connected to equipment in areas remote from these frames.

Idle-Channel Noise - Noise that is present in a communications channel when no signals are applied. Note: The channel conditions and terminations must be stated for idle-channel noise measurements to be meaningful.

Idle Character - A control character that is transmitted when no useful information is being transmitted.

Idle Code - A special sequence that indicates that no data are being sent on the channelized side.

Idle-Line Termination - A switch-controlled electrical network that maintains a desired impedance at a trunk or line terminal that is in the idle state.

Idle State - The telecommunications service condition that exists whenever user messages are not being transmitted but the service is immediately available for use.

Idle Time - A period during which a system, circuit, or component is not in use, but is available.

IDN - Abbreviation for integrated digital network. A network that uses both digital transmission and digital switching.

IDTV - Abbreviation for improved-definition television. - Television transmitters and receivers that (a) are built to satisfy performance requirements over and above those required by the NTSC standard and (b) remain within the general parameters of NTSC standard emissions. Note 1: IDTV improvements may be made at the TV transmitter or the receiver. Note 2: Examples of improvements include enhancements in encoding, digital filtering, scan interpolation, interlaced line scanning, and ghost cancellation. Note 3: IDTV improvements must allow the TV signal to be transmitted and received in the standard 4:3 aspect ratio. Synonym enhanced-quality television.

IETF - Abbreviation for Internet Engineering Task force. One of the task forces (with more than 40 working groups) of the Internet Architecture Board, responsible for solving short-term engineering needs of the Internet.

IF - Abbreviation for intermediate frequency. A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception.

I/F - I/F: Abbreviation for interface.- 1. In a system, a shared boundary, i.e., the boundary between two subsystems or two devices. 2. A shared boundary between two functional units, defined by specific attributes, such as functional characteristics, common physical interconnection characteristics, and signal characteristics. 3. A point of communication between two or more processes, persons, or other physical entities. 4. A point of interconnection between user terminal equipment and commercial communications facilities. 5. To interconnect two or more entities at a common point or shared boundary. 6. [A] common boundary between independent systems or modules where interactions take place. 7. The point of interconnection between two distinct but adjacent communications systems having different functions. The interface in the communication-satellite service is that point where communications terminal equipment of the terrestrial common carriers or other authorized entities interconnects with the terminal equipment of the communication-satellite earth station complex. The interface in the communication-satellite service shall be located at the earth station site, or if this is impracticable, as close thereto as possible.

IFF - Abbreviation for identification, friend or foe.- A system using electromagnetic transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. Note: The secondary surveillance radar (SSR) system used in modern air traffic control systems is an outgrowth of the military IFF system used during World War II. The IFF equipment carried by modern military aircraft is compatible with the transponder system used for civilian air traffic control.

IF4 (Interface 4) - An interface suitable for multipoint concentration by polling.

IF1 (Interface 1) - An interface suitable for star concentration.

IFRB - Abbreviation for International Frequency Registration Board. See Radio Regulations Board. The Radio Regulations Board was formerly called International Frequency Registration Board (IFRB). A permanent organization of the International Telecommunication Union (ITU) that implements frequency assignment policy and maintains the Master International Frequency Register (MIFR).

IF Repeater - See heterodyne repeater. In radio reception and retransmission, a repeater that converts the original band of frequencies of the received signal to a different frequency band for retransmission after amplification. Note: IF repeaters are used, for example, in microwave systems, to avoid undesired feedback between the receiving and transmitting antennas.

IFS - Abbreviation for ionospheric forward scatter. See ionospheric scatter. ionospheric scatter: The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere. Synonym forward propagation ionospheric scatter.

IF6 (Interface 6) - An interface between a network element (NE) to one or more network elements (NEs) in other locations using star configuration embedded operations channel (EOCs) or conventional communications services.

IF2 (Interface 2) - An interface suitable for communication between a network element (NE) location and operations systems (OSs) over packet switched networks, dedicated lines, or circuit switched connections.

ILD - Abbreviation for injection laser diode.

ILEC - Incumbent Local Exchange Carrier. The existing local exchange carrier in any given area, as opposed to CLECs.

Illegal Character - A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. Synonyms false character, forbidden character, improper character, unallowable character, unused character.

ILS - Abbreviation for instrument landing system. - 1. A radio-navigation system which provides aircraft with horizontal and vertical guidance just before and during landing and, at certain fixed points, indicates the distance to the reference point of landing. 2. A system of radio navigation intended to assist aircraft in landing which provides lateral and vertical guidance, which may include indications of distance from the optimum point of landing.

IM - Abbreviation for intensity modulation, intermodulation. The production, in a nonlinear element of a system, of frequencies corresponding to the sum and difference frequencies of the fundamentals and harmonics thereof that are transmitted through the element.

Image - In the field of image processing, a two-dimensional representation of a scene. Synonym picture.

Image Antenna - A hypothetical mirror-image, i.e., virtual-image, of an antenna, i.e., antenna element, considered to extend as far below ground, i.e., the ground plane, as the actual antenna is above the ground plane. Note 1: The image antenna is helpful in calculating electric field vectors, magnetic field vectors, and electromagnetic fields emanating from the real antenna, particularly in the vicinity of the antenna and along the ground. Each charge and current in the real antenna has its image that may also be considered as a source of radiation equal to, but differently directed from, its real counterpart. Note 2: An image antenna may also be considered to be on the opposite side of any equipotential plane surface, such as a metal plate acting as a ground plane, analogous to the position of a virtual optical image in a plane mirror. Note 3: The ground plane need not be grounded to the Earth.

Image Capture - The transducing of the information in a real image into the photographic or electronic medium. Note: Normally in motion-reproducing systems, synchronous audio information is simultaneously transduced.

Image Compression - 1. Application of an appropriate transfer function to an image signal so as to limit dynamic range. 2. Application of bandwidth limiting or bit-rate reduction to an image signal in order to bring it within the limitations of a lower capacity channel.

Image Enhancement - In video technology, a technique used to improve contrast and picture clarity by flattening the camera response to 400 lines (by aperture correction) and applying an additional correction to increase the depth of modulation in the range of 250 to 300 lines (in an NTSC system), both vertically and horizontally. Note: Image enhancement produces a correction signal with symmetrical overshoots around transitions in the picture, but it must be used sparingly if natural appearance is to be maintained.

Image File Architecture - The formalization of a multidisciplinary agreement—regarding digital image characteristics, such as the structure of digital image files, the organization of the image data itself, and the definition of fully flexible, interoperable, scalable, and extensible systems—which agreement facilitates the exchange of such files across various technology interfaces.

Image File Descriptor - A block of data that (a) may contain, in standardized format, data concerning production, ownership, access, previous processing, etc., relevant to the basic interpretation of the data, and (b) enhances the utility of the main data for the user.

Image File Header - A compact label for image files, created using a universally accepted algorithm, that (a) identifies the encoding standard, (b) specifies the length of the file, (c) indicates whether a readable descriptor is included, (d) permits random interception of data stream, and (d) offers optional error protection.

Image File Motion-Picture Format - The defining file format for exchange of digital motion-picture information on a variety of media between computer-based systems. Note: This flexible file format describes pixel-based (raster) images with attributes defined in the binary file descriptor—which identifies (a) generic file information, image information, data format, and image orientation information; (b) motion-picture and television industry-specific information; and (c) user defined information. The format assumes non real-time application, with accommodation for real-time to be considered as the developing technology permits.

Image File Video Index - A recommended practice intended to provide a method of coding video index information in which various picture- and program-related source data can be carried in conjunction with the video signal. Note: There are three classes of video index data based on type and use of the data. Class 1 contains information that is required to know how to use the signal. Class 2 contains heritage information for better usage of the signal. Class 3 contains other information not required to know how to use the signal.

Image Frequency - In radio reception using heterodyning in the tuning process, an undesired input frequency that is capable of producing the same intermediate frequency (IF) that the desired input frequency produces. Note: The term image arises from the mirror-like symmetry of signal and image frequencies about the beating-oscillator frequency.

Image Frequency Rejection Ratio - In reception using heterodyning in the tuning process, the ratio of (a) the intermediate-frequency (IF) signal level produced by the desired input frequency to (b) that produced by the image frequency. Note 1: The image rejection ratio is usually expressed in dB. Note 2: When the image rejection ratio is measured, the input signal levels of the desired and image frequencies must be equal for the measurement to be meaningful. Synonym image rejection ratio.

Image Generation - The creation of an image from an image concept. Note: The image can be created with computer-graphics software or photography, for example.

Image Map - A Web page feature in which hyperlinks are assigned ("mapped") to different portions of a graphic image, thereby allowing users to access links by clicking with a mouse on the mapped areas. Note: Image map requests are processed by CGI scripts on the server.

Image Rejection Ratio - In reception using heterodyning in the tuning process, the ratio of (a) the intermediate-frequency (IF) signal level produced by the desired input frequency to (b) that produced by the image frequency. Note 1: The image rejection ratio is usually expressed in dB. Note 2: When the image rejection ratio is measured, the input signal levels of the desired and image frequencies must be equal for the measurement to be meaningful. Synonym image frequency rejection ratio.

Imagery - Collectively, the representations of objects reproduced electronically or by optical means on film, electronic display devices, or other media.

IMD - Abbreviation for intermodulation distortion. - Nonlinear distortion characterized by the appearance, in the output of a device, of frequencies that are linear combinations of the fundamental frequencies and all harmonics present in the input signals. Note: Harmonic components themselves are not usually considered to characterize intermodulation distortion. When the harmonics are included as part of the distortion, a statement to that effect should be made.

Imitative Communications - See communications deception. 1. Deliberate transmission, retransmission, or alteration of communications to mislead an adversary's interpretation of the communications. 2. Use of devices, operations, and techniques with the intent of confusing or misleading the user of a communications link or a navigation system.

Immediate Action Limit (IAL) - The bound on performance allowed for a circuit or connection that is in service. When any parameter value exceeds the IAL, the circuit or connection is considered defective and corrective action is necessary.

Immediate Activation - In cryptology, a condition of readiness associated with a key having no effective date. Note: A key is immediately activated (a) by the receiver when the RSM is sent in response to the KSM that carried that key, and (b) by the sender when the RSM is received in response to the KSM that carried the key.

Immediate Message - A category of precedence reserved for messages relating to situations that gravely affect the security of national/allied forces or populace and that require immediate delivery to the addressee(s).

Immunity - The ability of an assembly, equipment, or a system to perform without degradation in the presence of an electromagnetic disturbance.

IMP - Abbreviation for interface message processor. - A processor-controlled switch used in packet-switched networks to route packets to their proper destination.

Impedance - The total passive opposition offered to the flow of electric current. Note 1: Impedance is determined by the particular combination of resistance, inductive reactance, and capacitive reactance in a given circuit. Note 2: Impedance is a function of frequency, except in the case of purely resistive networks.

Impedance Matching - The connection of an additional impedance to an existing one in order to accomplish a specific effect, such as to balance a circuit or to reduce reflection in a transmission line.

Impersonating - [A] form of spoofing. Spoofing is the interception, alteration, and retransmission of a cipher signal or data in such a way as to mislead the recipient. 2. (AIS) [An] attempt to gain access to an AIS by posing as an authorized user. [NIS] 3. Unauthorized use of legitimate Identification and Authentication (I&A) data, however it was obtained, to mimic a subject different from the attacker. Impersonating, masquerading, piggybacking, and mimicking are forms of spoofing.

Implant - [In security, an] electronic device or electronic equipment modification designed to gain unauthorized interception of information-bearing emanations.

Implicit Congestion Control - A scheme under which user terminals first detect a possible congestion condition by means other than explicit congestion messages, and then take appropriate action to reduce their throughput.

Improper Character - Synonym illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code.

Improved-Definition Television (IDTV) - Television transmitters and receivers that (a) are built to satisfy performance requirements over and above those required by the NTSC standard and (b) remain within the general parameters of NTSC standard emissions. Note 1: IDTV improvements may be made at the TV transmitter or the receiver. Note 2: Examples of improvements include enhancements in encoding, digital filtering, scan interpolation, interlaced line scanning, and ghost cancellation. Note 3: IDTV improvements must allow the TV signal to be transmitted and received in the standard 4:3 aspect ratio. Synonym enhanced-quality television.

Improvement Threshold - See FM improvement threshold. The point in an FM receiver at which the peaks in the rf signal equal the peaks of the thermal noise generated in the receiver. Note: A baseband signal-to-noise ratio of about 30 dB is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of increase in the signal above the threshold.

Impulse - A short surge of electrical, magnetic, or electromagnetic energy. Synonym surge.

Impulse Excitation - The production of oscillation in a circuit or device by impressing a stimulus (signal) for a period that is extremely short compared to the duration of the oscillation that it produces. Synonym shock excitation.

Impulse Noise - Noise consisting of random occurrences of energy spikes having random amplitude and spectral content. Note: Impulse noise in a data channel can be a definitive cause of data transmission errors.

Impulse Response - 1. Of a device, the mathematical function that describes the output waveform that results when the input is excited by a unit impulse. 2. The waveform that results at the output of a device when the input is excited by a unit impulse.

IN - Abbreviation for intelligent network. - 1. A network that allows functionality to be distributed flexibly at a variety of nodes on and off the network and allows the architecture to be modified to control the services. 2. In North America, an advanced network concept that is envisioned to offer such things as (a) distributed call-processing capabilities across multiple network modules, (b) real-time authorization code verification, (c) one-number services, and (d) flexible private network services [including (1) reconfiguration by subscriber, (2) traffic analyses, (3) service restrictions, (4) routing control, and (5) data on call histories]. Levels of IN development are identified below:

• IN/1 A proposed intelligent network targeted toward services that allow increased customer control and that can be provided by centralized switching vehicles serving a large customer base.
• IN/1+ A proposed intelligent network targeted toward services that can be provided by centralized switching vehicles, e.g., access tandems, serving a large customer base.
• IN/2 A proposed, advanced intelligent-network concept that extends the distributed IN/1 architecture to accommodate the concept called " service independence." Note: Traditionally, service logic has been localized at individual switching systems. The IN/2 architecture provides flexibility in the placement of service logic, requiring the use of advanced techniques to manage the distribution of both network data and service logic across multiple IN/2 modules.

Inactive Signaling Link - A signaling link that has been deactivated and cannot therefore carry signaling traffic.

In-band - Using or involving the information digit time slots of a DS1 frame; i.e., bit assignments of a frame exclusive of the framing bit.

In-band Control - Control effected by sending control information over the same channel as the one used to send data.

In-band Noise Power Ratio - For multichannel equipment, the ratio of (a) the mean noise power measured in any channel, with all channels loaded with white noise, to (b) the mean noise power measured in the same channel, with all channels but the measured channel loaded with white noise.

In-band Signaling - Signaling that uses frequencies or time slots within the bandwidth or data stream occupied by the information channel.

In Call - A UPT (Universal Personal Telecommunications) call type which permits a UPT user to have calls to his/her UPT number routed to the terminal specified by the user.

In call Delivery - A feature by which incoming calls are presented at the terminal address registered previously by in-call registration. This feature is invoked when originating parties or others call the UPT (Universal Personal Telecommunications service) user.

In-call Registration - A feature that enables the UPT (Universal Personal Telecommunications service) user to register from the current terminal address for incoming calls to be presented to that terminal address. When registered, all incoming calls to the UPT number of the UPT user will be presented to the registered terminal address, for the duration specified by the UPT user (duration may also be specified in terms of number of incoming UPT calls), or until a specified deregistration time. A UPT user's in-call registration will cancel the previous in-call registration of that UPT user's UPT number. Several UPT users may register for incoming calls to the same terminal address simultaneously. The UPT user may also explicitly de-register for incoming calls.

Incident - 1. In information systems (IS), [an] assessed occurrence having actual or potentially adverse effects on an IS. 2. In COMSEC, the occurrence that potentially jeopardizes the security of COMSEC material or the secure electrical transmission of national security information or information governed by 10 U.S.C. Section 2315.

Incidental-Radiation Device - A device that radiates radio frequency energy during the course of its operation although the device is not intentionally designed to generate radio frequency energy.

Inclination of an Orbit (of an Earth satellite) - The angle determined by the plane containing the orbit and the plane of the Earth's equator.

Inclined Orbit - Any nonequatorial orbit of a satellite. Note: Inclined orbits may be circular or elliptical, synchronous or asynchronous, and direct or retrograde.

Inclusion - A foreign object present within, for example, an optical fiber or a crystal.

Incoherent - In optics, characterized by a degree of coherence significantly less than 0.88.

Incoming Access - The ability of a user to terminate data calls via an ISDN.

Incoming Call Identification (ICI) - A switching system feature that allows an attendant to identify visually the type of service or trunk group associated with a call directed to the attendant's position.

Incorrect Block - A block successfully delivered to the intended destination user, but having one or more incorrect bits, additions, or deletions, in the delivered block.

Incremental Compaction - Data compaction accomplished by specifying only the initial value and all subsequent changes. Note: An example of incremental compaction is the storing or transmitting of a line voltage followed only by the deviations from the initial value. Thus, instead of transmitting the values 102, 104, 105, 103, 100, 104 and 106, only the values 102, +2, +1, -2, -3, +4, and +2, or only the values 100, +2, +4, +5, +3, 0, +4, and +6 need be sent, depending on the system used. At a given data rate, transmitting only the initial and incremental values require much less time and space than transmitting the absolute values.

Incremental Phase Modulation (IPM) - In spread-spectrum systems, phase modulation in which one binary code sequence is shifted with respect to another, usually to conduct a synchronizing search, i.e., a search to discover if the two sequences are the same, and perhaps thereby enabling two data streams to be synchronized.

Indefinite Call Sign - 1. A call sign that represents a group of facilities, commands, authorities, activities, or units rather than one of these. 2. In radio communications, a call sign that does not identify a station and that is used in the call-up signal or in a message that has the station call sign encrypted in the text.

Independent Clocks - In communication network timing subsystems, free-running precision clocks used, for synchronization purposes, at the nodes. Note: Variable storage buffers, installed to accommodate variations in transmission delay between nodes, are made large enough to accommodate small time (phase) departures among the nodal clocks that control transmission. Traffic may occasionally be interrupted to allow the buffers to be emptied of some or all of their stored data.

Independent-Sideband (ISB) Transmission - Double-sideband transmission in which the information carried by each sideband is different. Note: The carrier may be suppressed.

Independent Telephone Company - A telephone company not affiliated with any of the original Bell telephone companies. See RBOC.

Index Dip - In an optical fiber, an undesired decrease in the refractive index at the center of the core. Note: An index dip is an artifact of certain manufacturing processes. Synonym profile dip.

Indexing - See interaction crosstalk. Crosstalk caused by coupling between carrier and noncarrier circuits. Note: If the interaction crosstalk is, in turn, coupled to another carrier circuit, that crosstalk is called "indexing."

Index-Matching Gel - Synonym gel. 1. A substance, resembling petroleum jelly in viscosity, that surrounds a fiber, or multiple fibers, enclosed in a loose buffer tube. Note: This gel serves to lubricate and support the fibers in the buffer tube. It also prevents water intrusion in the event the buffer tube is breached. 2. Index-matching material in the form of a gel. Synonym matching gel.

Index-Matching Material - A substance, usually a liquid, cement (adhesive), or gel, which has an index of refraction that closely approximates that of an optical fiber, and is used to reduce Fresnel reflection at the fiber endface. (FAA) Note 1: An index-matching material may be used in conjunction with pairs of mated connectors, with mechanical splices, or at the ends of fibers. Note 2: Without the use of an index-matching material, Fresnel reflections will occur at the smooth endfaces of a fiber. These reflections may be as high as -14 dB (i.e., 14 dB below the level of the incident signal). When the reflected signal returns to the transmitting end, it is reflected again and returns to the receiving end at a level that is (28 plus twice the fiber loss) dB below the direct signal. The reflected signal will also be delayed by twice the delay time introduced by the fiber. The reflected signal will have no practical effect on digital systems because of its low level relative to the direct signal; i.e., it will have no practical effect on the detected signal seen at the decision point of the digital optical receiver. It may be noticeable in an analog baseband intensity-modulated video signal.

Index of Cooperation - 1. In facsimile, the product of the total line length and the number of lines per unit length, divided by . 2. For rotating devices, the product of the drum diameter and the number of lines per unit length. Synonyms: diametral index of cooperation, international index of cooperation.

Index of Refraction - Synonym refractive index. (, n): Of a medium, the ratio of the velocity of propagation of an electromagnetic wave in vacuum to its velocity in the medium. Note: When the Greek character eta is unavailable, the letter n is used to represent the refractive index.

Index Profile - Synonym refractive index profile. Of the cross section of an optical fiber, the description, i.e., plot, of the value of the refractive index as a function of distance from the fiber axis along a diameter.

Index Profile - Refractive Index Profile

Indirect Control - In digital data transmission, the use of a clock rate of 2ⁿ times the modulation rate, where n is an integer greater than one.

Indirect Wave - A wave, such as a radio wave or sound wave, that arrives at a given point by reflection or scattering from surrounding objects, rather than directly from the source.

Individual Line - A line that connects a single user to a switching center.

Individual Reception (in the broadcasting-satellite service) - The reception of emissions from a space station in the broadcasting-satellite service by simple domestic installations and in particular those possessing small antennae.

Inductive Coupling - The transfer of energy from one circuit to another by virtue of the mutual inductance between the circuits. Note 1: Inductive coupling may be deliberate and desired (as in an antenna coupler) or may be undesired (as in power line inductive coupling into telephone lines). Note 2: Capacitive coupling favors transfer of higher frequency components, whereas inductive coupling favors transfer of lower frequency components.

Industrial, Scientific, and Medical (ISM) Applications (of radio frequency energy) - Operation of equipment or appliances designed to generate and use locally radio-frequency energy for industrial, scientific, medical, domestic or similar purposes, excluding applications in the field of telecommunications.

Industry Standard - A voluntary, industry-developed document that establishes requirements for products, practices, or operations.

Infobahn - A slang term for The Internet or NII. See National Information Infrastructure. A proposed, advanced, seamless web of public and private communications networks, interactive services, interoperable hardware and software, computers, databases, and consumer electronics to put vast amounts of information at users' fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners, keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire, satellites, optical fiber transmission lines, microwave nets, switches, televisions, monitors, and printers) used to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive functions, user-tailored services, and multimedia databases that are interconnected in a technology-neutral manner that will favor no one industry over any other. Synonym information superhighway.

Infobot - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme.

Information - 1. Facts, data, or instructions in any medium or form. 2. The meaning that a human assigns to data by means of the known conventions used in their representation.

Information agent - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme.

Information Assurance - Information operations (IO) that protect and defend information and information systems (IS) by ensuring their availability, integrity, authentication, confidentiality, and nonrepudiation. This includes providing for restoration of information systems by incorporating protection, detection, and reaction capabilities.

Information-Bearer Channel - 1. A channel capable of transmitting all the information required for communication, such as user data, synchronizing sequences, and control signals. Note: The information-bearer channel may operate at a higher data rate than that required for user data alone. 2. A basic communications channel with the necessary bandwidth but without enhanced or value-added services.

Information Bit - See user information bit. A bit transferred from a source user to a telecommunications system for delivery to a destination user. Note 1: User information bits do not include the overhead bits originated by, or having their primary functional effect within, the telecommunications system. Note 2: User information bits are encoded to form channel bits.

Information Digit(s) - A single-digit data element in the 7-digit format that is outpulsed by the network to indicate the numbering plan digit (NPD) and CESID (caller's emergency service ID) display status. In the 10-digit format, two information digits used to indicate the CESID display status. The information digit or digits can also indicate a maintenance test call.

Information Feedback - The return of received data to the source, usually for the purpose of checking the accuracy of transmission by comparison with the original data.

Information Field - In data transmission, a field assigned to contain user information. Note: The contents of the information field are not interpreted at the link level.

Information Flow Control - A procedure to ensure that information transfers within an information system (IS) are not made from a higher security level object to an object of a lower security level.

Information Integrity - In a frame-relaying network, the condition when all frames relayed by the network satisfy the frame check sequence check.

Information Origination/Termination Equipment - Equipment used to input into or receive output from the telecommunications network.

Information processing - Synonym data processing.The systematic performance of operations upon data such as handling, merging, sorting, and computing. Note: The semantic content of the original data should not be changed. The semantic content of the processed data may be changed.

Information processing center (IPC): A facility staffed and equipped for processing and distributing information. Note: An IPC may be geographically distributed.

Information Provider - An entity that collects information and makes it available to Internet users. Note: The information can be provided directly to users, or provided via an Internet access provider or a content provider.

Information Rate - For a frame relay logical connection, the average number of end user bits transferred per second, in one direction, across a user-network interface as measured over an interval of duration 't'. The measurement interval 't' is network dependent.

Information Security - The protection of information against unauthorized disclosure, transfer, modification, or destruction, whether accidental or intentional.

Information Source - Synonym source user. The user providing the information to be transferred to a destination user during a particular information transfer transaction.

Information Superhighway - Synonym National Information Infrastructure. A proposed, advanced, seamless web of public and private communications networks, interactive services, interoperable hardware and software, computers, databases, and consumer electronics to put vast amounts of information at users' fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners, keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire, satellites, optical fiber transmission lines, microwave nets, switches, televisions, monitors, and printers) used to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive functions, user-tailored services, and multimedia databases that are interconnected in a technology-neutral manner that will favor no one industry over any other.

Information System - 1. A system, whether automated or manual, that comprises people, machines, and/or methods organized to collect, process, transmit, and disseminate data that represent user information. 2. Any telecommunications and/or computer related equipment or interconnected system or subsystems of equipment that is used in the acquisition, storage, manipulation, management, movement, control, display, switching, interchange, transmission, or reception of voice and/or data, and includes software, firmware, and hardware. 3. The entire infrastructure, organization, personnel, and components for the collection, processing, storage, transmission, display, dissemination, and disposition of information.

Information Systems Security (INFOSEC and/or ISS) - [The] protection of information systems against unauthorized access to or modification of information, whether in storage, processing or transit, and against the denial of service to authorized users, including those measures necessary to detect, document, and counter such threats.

Information Technology (IT) - The branch of technology devoted to (a) the study and application of data and the processing thereof; i.e., the automatic acquisition, storage, manipulation (including transformation), management, movement, control, display, switching, interchange, transmission or reception of data, and (b) the development and use of the hardware, software, firmware, and procedures associated with this processing.

Information Transfer - The process of moving messages containing user information from a source to a sink. Note: The information transfer rate may or may not be equal to the transmission modulation rate.

Information Transfer Capability - The capability associated with the transfer of different types of information through the ISDN. It can be used to characterize a telecommunication service or connection. Values associated with this attribute are unrestricted digital, speech, 3.1-kHz audio, 7- kHz audio, 15-kHz audio, and video.

Information Transfer Interface - Establishment of a communication (signaling) path and any required bearer path between the RPT/RT and the radio port. For example, in TDMA and FDMA, time slots and frequencies are identified, and in CDMA, sequence codes are identified.

Information Transfer Mode - The operational mode for transferring (transportation and switching) user information through the ISDN. It can be used to characterize a telecommunication service or a connection in the network. Values associated with the attribute are circuit mode and packet mode.

Information-Transfer Phase - In an information-transfer transaction, the phase during which user information blocks are transferred from the source user to a destination user.

Information Transfer Rate - The transfer of digital information between two access points or reference points. Values associated with this attribute are appropriate bit rate (in circuit mode) and throughput rate (in packet mode).

Information-Transfer Transaction - A coordinated sequence of user and telecommunications system actions that cause information present at a source user to become present at a destination user. Note: An information-transfer transaction usually consists of three consecutive phases called the access phase, the information-transfer phase, and the disengagement phase.

INFOSEC - Acronym for information systems security. [The] protection of information systems against unauthorized access to or modification of information, whether in storage, processing or transit, and against the denial of service to authorized users, including those measures necessary to detect, document, and counter such threats.

Infrared (IR) - The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (approximately 0.7 m) and the shortest microwaves (approximately 0.1 mm). See electromagnetic spectrum.

Ink Vapor Recording - Recording in which vaporized ink particles are deposited directly upon the record medium.

Infrastructure Assurance - Preemptive or reactive risk-management techniques designed to increase confidence that disruption of a system will be minimized if its critical infrastructure is attacked.

Infrastructure Protection - Preemptive or reactive risk-management techniques designed to prevent disruption of a system after its critical infrastructure is attacked.

Inhibiting Signal - A signal that prevents the occurrence of an event. Note: An inhibiting signal may be used, for example, to disable an AND gate, thus preventing any signals from passing through it as long as the inhibiting signal is present.

Initial Alignment - A procedure used to qualify a signaling link for carriage of signaling traffic, either for the first time orinitial alignment: A procedure used to qualify a signaling link for carriage of signaling traffic, either for the first time or after failure has occurred. after failure has occurred.

Iinitialization Vector - In encryption, a nonsecret binary vector used as the initializing input algorithm for the encryption of a plaintext block sequence to increase security by introducing additional cryptographic variance and to synchronize cryptographic equipment.

Initialize - Setting the state of a cryptographic logic prior to key generation, encryption, or other operating mode.

Initial Text Sequence - In cryptography, a 64-bit binary sector that may be attached to the beginning of a message.

Initiating MSC - The mobile switching center (MSC) (switch) that obtains routing information (i.e., LRN).

Injection Fiber - Synonym launching fiber. An optical fiber used in conjunction with a source to excite the modes of another fiber in a particular fashion. Note: Launching fibers are most often used in test systems to improve the precision of measurements.

Injection Laser Diode (ILD) - A laser that uses a forward-biased semiconductor junction as the active medium. Note: Stimulated emission of coherent light occurs at a p-n junction where electrons and holes are driven into the junction. Synonyms diode laser, laser diode, semiconductor laser.

Ink Vapor Recording - Recording in which vaporized ink particles are deposited directly upon the record medium.

Inline - An image on a web page that is displayed directly to the viewer rather than being made available only as a hot link.

Input - 1. In a device, process, or channel, a point that accepts data. 2. A state, or a sequence of states, of a point that accepts data. 3. A stimulus, such as a signal or interference, that enters a functional unit, such as a telecommunications system, a computer, or a computer program.

Input Data - 1. Data being received or to be received by a device or a computer program. 2. Data to be processed.

Input Focus - The attribute of a user interface component, such as a window, that enables it to receive input from a particular input device, such as the keyboard.

Input-Output Channel - For a computer, a device that handles the transfer of data between internal memory and peripheral equipment.

Input-Output Controller (IOC) - A functional unit that controls one or more input-output channels. Synonym I/O controller.

Input/Output (I/O) Device - A device that introduces data into or extracts data from a system.

Input Protection - For analog input channels, protection against overvoltages that may be applied between any two input connectors or between any input connector and ground.

Insertion Gain - The gain resulting from the insertion of a device in a transmission line, expressed as the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Note 1: If the resulting number is less than unity, an " insertion loss " is indicated. Note 2: Insertion gain is usually expressed in dB.

Insertion Loss - 1. The loss resulting from the insertion of a device in a transmission line, expressed as the reciprocal of the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Note: Insertion loss is usually expressed in dB. 2. In an optical fiber system, the total optical power loss caused by insertion of an optical component, such as a connector, splice, or coupler.

Insertion-Loss-vs.-Frequency Characteristic - Of a system or device, a plot of the amplitude as a function of frequency. Note: The insertion-loss-vs.-frequency characteristic may be expressed as absolute gain or loss, or it may be normalized with respect to gain or loss at a specified reference frequency.

Inside Call - Synonym internal call. A call placed within a private branch exchange (PBX) or local switchboard, i.e., not through a central office in a public switched network.

Inside Plant - 1. All the cabling and equipment installed in a telecommunications facility, including the main distribution frame (MDF) and all the equipment extending inward therefrom, such as PABX or central office equipment, MDF protectors, and grounding systems. 2. In radio and radar systems, all communications-electronics (C-E) equipment that is installed in buildings.

Inside Wire - See on-premises wiring. Customer-owned metallic or optical-fiber communications transmission lines, installed within or between buildings. Note: On-premises wiring may consist of horizontal wiring, vertical wiring, and backbone wiring, and may extend from the external network interface to the user work station areas. It includes the total communications wiring to transport current or future data, voice, LAN, and image information.

In-Slot Signaling - Signaling performed in the associated channel time slot.

Inspection Lot - A collection of produced units from which a statistically valid sample is to be drawn and inspected to determine conformance with acceptability criteria. Note: The inspection lot may differ from a collection of units designated as a lot for other purposes, such as for production, storage, packaging, and shipment.

Instantiation - the process of creating a managed object according to a managed object class definition.

Instruction - In a programming language, an expression that specifies one operation and identifies its operands, if any.

Instructional Television Fixed Station - A fixed station operated by an educational organization and used primarily for the transmission of visual and aural instructional, cultural, and other types of educational material to one or more fixed receiving locations.

Instrument Landing System (ILS) - 1. A radio-navigation system which provides aircraft with horizontal and vertical guidance just before and during landing and, at certain fixed points, indicates the distance to the reference point of landing. 2. A system of radio navigation intended to assist aircraft in landing which provides lateral and vertical guidance, which may include indications of distance from the optimum point of landing.

Instrument Landing System Glide Path - A system of vertical guidance embodied in the instrument landing system which indicates the vertical deviation of the aircraft from its optimum path of descent.

Instrument Landing System Localizer - A system of horizontal guidance embodied in the instrument landing system which indicates the horizontal deviation of the aircraft from its optimum path of descent along the axis of the runway.

Insulated Wire - Telecommunications plant containing from one to six paired conductors, and possibly a shield. Wire may be found in either aerial or buried installations.

Integrated Circuit (IC) - An electronic circuit that consists of many individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other active and passive semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of substrate material. Synonyms chip, microcircuit.

Integrated Digital Network (IDN) - A network that uses both digital transmission and digital switching.

Integrated Ground Plane - A set of interconnected frames that is intentionally grounded via multiple connections to a ground reference. Multiple connections are intended to keep voltage drops (due to power faults in the ac or dc power systems or from lightning) to acceptable levels. The following are examples of an integrated ground plane: building steel, water pipes, ground rod systems, counterpoises, vertical and horizontal ground reference conductors, grounding (earthing) wires, and metallic raceways form an integrated ground plane when bonded together by a multiplicity of both deliberate and incidental connections. Synonym common bonding network (CBN).

Integrated Optical Circuit (IOC) - A circuit, or group of interconnected circuits, consisting of miniature solid-state optical components on semiconductor or dielectric substrates. Note: IOC components include light sources, optical filters, photodetectors, and thin-film optical waveguides.

Integrated Services Digital Network (ISDN) - A high performance, digital phone circuit available from most regional telephone companies that allows for voice and data to be transmitted on the same line, producing fast, noise-free connections. - See ISDN. An integrated digital network in which the same time-division switches and digital transmission paths are used to establish connections for different services. Note 1: ISDN services include telephone, data, electronic mail, and facsimile. Note 2: The method used to accomplish a connection is often specified: for example, switched connection, nonswitched connection, exchange connection, ISDN connection.

Integrated Station - A terminal device in which a telephone and one or more other devices, such as a video display unit, keyboard, or printer, are integrated and used over a single circuit.

Integrated System - A telecommunication system that transfers analog and digital traffic over the same switched network.

Integrated Voice and Data Terminal (IVDT) - See integrated station. A terminal device in which a telephone and one or more other devices, such as a video display unit, keyboard, or printer, are integrated and used over a single circuit.

Integrating Network - A network (circuit) that produces an output waveform that is the time integral of the input waveform. Note: Integrating networks are used in signal processing, such as for producing sawtooth waves from square waves.

Integrity - The quality of an information system (IS) reflecting the logical correctness and reliability of the operating system; the logical completeness of the hardware and software implementing the protection mechanisms; and the consistency of the data structures and occurrence of the stored data. Note that, in a formal security mode, integrity is interpreted more narrowly to mean protection against unauthorized modification or destruction of information.

Integrity Check Value - A checksum capable of detecting modification of an information system (IS).

Intelligent Agent - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme.

Intelligent Network (IN) - 1. A network that allows functionality to be distributed flexibly at a variety of nodes on and off the network and allows the architecture to be modified to control the services. 2. In North America, an advanced network concept that is envisioned to offer such things as (a) distributed call-processing capabilities across multiple network modules, (b) real-time authorization code verification, (c) one-number services, and (d) flexible private network services [including (1) reconfiguration by subscriber, (2) traffic analyses, (3) service restrictions, (4) routing control, and (5) data on call histories]. Levels of IN development are identified below:

• IN/1 A proposed intelligent network targeted toward services that allow increased customer control and that can be provided by centralized switching vehicles serving a large customer base.
• IN/1+ A proposed intelligent network targeted toward services that can be provided by centralized switching vehicles, e.g., access tandems, serving a large customer base.
• IN/2 A proposed, advanced intelligent-network concept that extends the distributed IN/1 architecture to accommodate the concept called " service independence." Note: Traditionally, service logic has been localized at individual switching systems. The IN/2 architecture provides flexibility in the placement of service logic, requiring the use of advanced techniques to manage the distribution of both network data and service logic across multiple IN/2 modules.

Intelligent Network Application Protocol (INAP) - A protocol for intelligent network applications contained in Layer 7 (the Application Layer of the OSI model).

Intelligent Network (IN) Supported Service - A service provided using the capabilities of the intelligent network.

Intelligent Peripheral (IP) - 1. A functional component that may be used most efficiently when accessed locally. 2. An intelligent-network feature that provides specialized telecommunication capabilities required by IN/2 service logic programs.

Intelligibility - For voice communications, the capability of being understood. Note: Intelligibility does not imply the recognition of a particular voice.

Intelligible Crosstalk - Crosstalk from which information can be derived.

INTELSAT - Abbreviation for International Telecommunications Satellite Organization.

Intensity - The square of the electric field strength of an electromagnetic wave. Note: Intensity is proportional to irradiance and may be used in place of the term "irradiance" when only relative values are important.

Intensity Modulation (IM) - In optical communications, a form of modulation in which the optical power output of a source is varied in accordance with some characteristic of the modulating signal. Note: In intensity modulation, there are no discrete upper and lower sidebands in the usually understood sense of these terms, because present optical sources lack sufficient coherence to produce them. The envelope of the modulated optical signal is an analog of the modulating signal in the sense that the instantaneous power of the envelope is an analog of the characteristic of interest in the modulating signal. Recovery of the modulating signal is by direct detection, not heterodyning.

Interaction Crosstalk - Crosstalk caused by coupling between carrier and noncarrier circuits. Note: If the interaction crosstalk is, in turn, coupled to another carrier circuit, that crosstalk is called "indexing."

Interactive - Pertaining to a communications environment in which more than one party is equipped and ready to participate actively in a session or a protocol. [After X9.42] Note: Common usage of the term refers to a session where at least one of the parties is human and another of the parties is a software application.

Interactive Data Transaction - A unidirectional message, transmitted via a data channel, that requires a response in order for work to proceed logically.

Interactive Service - In an integrated services digital network (ISDN), a telecommunications service that facilitates a bidirectional exchange of information among users or among users and hosts. Note: Interactive services are grouped into conversational services, messaging services, and retrieval services.

Interactive Voice Response - In telephony, interactive voice response, or IVR, is a computerised system that allows a person, typically a telephone caller, to select an option from a voice menu and otherwise interface with a computer system. Generally the system plays pre-recorded voice prompts to which the person presses a number on a telephone keypad to select the option chosen, or speaks simple answers such as "yes", "no", or numbers in answer to the voice prompts.

The latest systems use natural language speech recognition to interpret the questions that the person wants answered.

Other innovations include the ability to speak complex and dynamic information such as an e-mail, news report or weather information using Text-To-Speech (TTS). TTS is computer generated synthesised speech and is no longer the robotic voice people associate with computers. Real voices are used to create the speech in tiny fragments that are glued together before being played to the caller.

IVR systems are found operating telephone banking services, voicemail systems are similar to IVR systems but offer limited functionality. IVR systems can be used to create services from telephone banking, order placement, caller identification and airline ticket booking. ACD systems are often the first point of contact when calling many larger businesses. IVR systems are generally used at the front end of call centers to identify what service the caller wants and to extract numeric information such as account numbers as well as provide answers to simple questions such as account balances or allow pre-recorded information to be heard.

IVR systems are often criticised as being unhelpful and difficult to use due to poor design and lack of appreciation of the callers' needs. A properly designed IVR system should connect callers to their desired service promptly and with a minimum of fuss.

IVR call flows are created in a variety of ways: while older systems depended upon proprietary programming or scripting languages, modern systems are structured similar to WWW pages, using the VoiceXML or SALT (http://www.saltforum.org/speechtek05/) language. This allows any Web server to act as an application server, freeing the developer to focus on the call flow. Developers then also no longer require specialized programming skills, as any Web developer already has all the tools needed to create an IVR call flow.

Interblock Gap - On a data recording medium, an area used to indicate the end of a block or physical record. Note: Examples of interblock gaps are the gaps between blocks on magnetic tape and disks.

Intercept - 1. To stop a telephone call directed to an improper, disconnected, or restricted telephone number, and to redirect that call to an operator or a recording. 2. To gain possession of communications intended for others without their consent, and, ordinarily, without delaying or preventing the transmission. Note: An intercept may be an authorized or unauthorized action. 3. The acquisition of a transmitted signal with the intent of delaying or eliminating receipt of that signal by the intended destination user. 4. A call disposition category for a call attempt to a non-operating number.

Intercept Call Request - An operator services call request initiated by the network because of the service condition of the line of the called party (e.g., line out of service, etc.).

Interchange - Mutual acceptance and exchange of messages between entities.

Interchangeability - 1. The ability to exchange hardware components having the same form, fit, and function, across platforms, without affecting the functionality of the system. 2. A condition which exists when two or more items possess such functional and physical characteristics as to be equivalent in performance and durability, and are capable of being exchanged one for the other without alteration of the items themselves, or of adjoining items, except for adjustment, and without selection for fit and performance.

Interchangeable Connectors - Connectors that share common installation geometry and have the same transmission performance.

Interchange Circuit - A circuit that facilitates the exchange of data and signaling information between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). Note: An interchange circuit can carry many types of signals and provide many types of service features, such as control signals, timing signals, and common return functions.

Intercharacter Interval - In asynchronous transmission, the time interval between the end of the stop signal of one character and the beginning of the start signal of the next character. Note: The intercharacter interval may be of any duration. The signal sense of the intercharacter interval is always the same as the sense of the stop element, i.e., "1" or "mark."

Intercom - 1. A telephone apparatus by means of which personnel can talk to each other within an aircraft, tank, ship, or activity. [JP 1-02] 2. A dedicated voice service within a specified user environment.

Interconnect Facility - In a communications network, one or more communications links that (a) are used to provide local area communications service among several locations and (b) collectively form a node in the network. Note 1: An interconnect facility may include network control and administrative circuits as well as the primary traffic circuits. Note 2: An interconnect facility may use any medium available and may be redundant.

Interconnecting Networks (ICNs) - Two or more networks connected for purposes of call processing.

Interconnection - 1. The linking together of interoperable systems. 2. The linkage used to join two or more communications units, such as systems, networks, links, nodes, equipment, circuits, and devices.

Interconnectivity - See interconnection. - 1. The linking together of interoperable systems. 2. The linkage used to join two or more communications units, such as systems, networks, links, nodes, equipment, circuits, and devices.

Interdigit Interval - A multifrequency (MF) and dual tone multifrequency (DTMF) signal timing interval that is equal to the sum of the fall time, signal-off time, and rise time. The interdigit interval starts when the MF or DTMF signal duration ends. The interdigit interval ends when the next MF or DTMF signal duration begins.

Interest Group - A gathering or category of network users who have a similar interest in a particular topic and who share their opinions with each other via email or an internet forum.

Interexchange Carrier (IXC or IC) - 1. A communications common carrier authorized to provide interexchange telecommunications services within world zone 1 using the North American numbering plan. 2. A telecommunications common carrier authorized to provide telecommunications services between LATAs. Note: The term "interexchange carrier" is also used to refer to any other entity that connects to the exchange access network at a point of termination (POT).3. A carrier that provides connections between LATAs, where the calling or called customer is located in the United States. Note: This definition has no Canadian equivalent. However, the term "interexchange carrier" is used in the context of a carrier that provides connections extending across borders to carriers in the United States. Synonyms [loosely] carrier, common carrier, commercial carrier, communications carrier.

Interexchange Channel - A circuit which is included in the interexchange transmission equipment.

Interexchange Transmission Equipment - The combination of (a) interexchange cable and wire facilities, (b) interexchange circuit equipment and, (c) associated land and buildings.

Interface (I/F) - 1. In a system, a shared boundary, i.e., the boundary between two subsystems or two devices. 2. A shared boundary between two functional units, defined by specific attributes, such as functional characteristics, common physical interconnection characteristics, and signal characteristics. 3. A point of communication between two or more processes, persons, or other physical entities. 4. A point of interconnection between user terminal equipment and commercial communications facilities. 5. To interconnect two or more entities at a common point or shared boundary. 6. [A] common boundary between independent systems or modules where interactions take place. 7. The point of interconnection between two distinct but adjacent communications systems having different functions. The interface in the communication-satellite service is that point where communications terminal equipment of the terrestrial common carriers or other authorized entities interconnects with the terminal equipment of the communication-satellite earth station complex. The interface in the communication-satellite service shall be located at the earth station site, or if this is impracticable, as close thereto as possible.

Interface Data - The parameter within a primitive that is the unit of information transferred to/from the upper layer or sublayer in a single interaction.

Interface Functionality - In telephony, the characteristic of interfaces that allows them to support transmission, switching, and signaling functions identical to those used in the enhanced services provided by the carrier. Note: As part of its comparably efficient interconnection (CEI) offering, the carrier must make available standardized hardware and software interfaces that are able to support transmission, switching, and signaling functions identical to those used in the enhanced services provided by the carrier.

Interface Message Processor (IMP) - A processor-controlled switch used in packet-switched networks to route packets to their proper destination.

Interface Payload - In integrated services digital networks (ISDN), the part of the bit stream through a framed interface used for telecommunications services and signaling.

Interface Point - Synonym point of interface. In a telecommunications system, the physical interface between the local access and transport area (LATA) access and inter-LATA functions. Note: The interface point is used to establish the technical interface, the test points, and the points of operational responsibility.

Interface Rate - The gross bit rate of the signal at the boundary between the physical layer and the physical medium.

Interface Standard - A standard that describes one or more functional characteristics (such as code conversion, line assignments, or protocol compliance) or physical characteristics (such as electrical, mechanical, or optical characteristics) necessary to allow the exchange of information between two or more (usually different) systems or equipment. Note 1: An interface standard may include operational characteristics and acceptable levels of performance. Note 2: In the military community, interface standards permit command and control functions to be performed using communication and computer systems.

Interference - 1. In general, extraneous energy, from natural or man-made sources, that impedes the reception of desired signals. 2. A coherent emission having a relatively narrow spectral content, e.g., a radio emission from another transmitter at approximately the same frequency, or having a harmonic frequency approximately the same as, another emission of interest to a given recipient, and which impedes reception of the desired signal by the intended recipient. Note: In the context of this definition, interference is distinguished from noise in that the latter is an incoherent emission from a natural source (e.g., lightning) or a man-made source, of a character unlike that of the desired signal (e.g., commutator noise from rotating machinery) and which usually has a broad spectral content. 3. The effect of unwanted energy due to one or a combination of emissions, radiation, or inductions upon reception in a radiocommunication system, manifested by any performance degradation, misinterpretation, or loss of information which could be extracted in the absence of such unwanted energy. 4. The interaction of two or more coherent or partially coherent waves, which interaction produces a resultant wave that differs from the original waves in phase, amplitude, or both. Note: Interference may be constructive or destructive, i.e., it may result in increased amplitude or decreased amplitude, respectively. Two waves equal in frequency and amplitude, and out of phase by 180°, will completely cancel one another. In phase, they create a resultant wave having twice the amplitude of either interfering beam.

Interference Emission - Emission that results in an electrical signal's being propagated into, and interfering with the proper operation of, electronic or electrical equipment. Note: The frequency range of interference emissions may include the entire electromagnetic spectrum.

Interference Filter - An optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. Note 1: An interference filter may be high-pass, low-pass, bandpass, or band-rejection. Note 2: An interference filter consists of multiple thin layers of dielectric material having different refractive indices. There also may be metallic layers. Interference filters are wavelength-selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries.

Interfering Contour - The locus of points surrounding a transmitter where the predicted median field strength of the signal from that transmitter is the maximum field strength that is not considered to cause interference at the service contour of another transmitter.

Interferometer - An instrument that uses the principle of interference of electromagnetic waves for purposes of measurement. Note: Interferometers may be used to measure a variety of physical variables, such as displacement (distance), temperature, pressure, and strain.

Interferometry - The branch of science devoted to the study and measurement of the interaction of waves, such as electromagnetic waves and acoustic waves. Note 1: The interaction of the waves can produce various spatial-, time-, and frequency-domain energy distribution patterns. Note 2: Interferometric techniques are used to measure refractive index profiles, e.g., those of the preforms from which optical fibers are drawn, and to sense and measure physical variables, such as displacement (distance), temperature, pressure, and magnetic fields.

Interframe Time Fill - In digital data transmission, a sequence of bits transmitted between consecutive frames. Note: Interframe time fill does not include bits stuffed within a frame.

Interlaced Scanning - In raster-scanned video displays, a scanning technique in which all odd-numbered scanning lines are first traced in succession, followed by the tracing of the even-numbered scanning lines in succession, each of which is traced between a pair of odd-numbered scanning lines. Note 1: The pattern created by tracing the odd-numbered scanning lines is called the odd field , and the pattern created by tracing the even-numbered scanning lines is called the even field. Each field contains half the information content, i.e., pixels, of the complete video frame. Note 2: Image flicker is less apparent in an interlaced display than in a noninterlaced display, because the rate at which successive fields occur in an interlaced display is twice that at which successive frames would occur in a noninterlaced display containing the same number of scanning lines and having the same frame refresh rate. Synonym interlacing.

Interlacing - Synonym interlaced scanning. In raster-scanned video displays, a scanning technique in which all odd-numbered scanning lines are first traced in succession, followed by the tracing of the even-numbered scanning lines in succession, each of which is traced between a pair of odd-numbered scanning lines. Note 1: The pattern created by tracing the odd-numbered scanning lines is called the odd field , and the pattern created by tracing the even-numbered scanning lines is called the even field. Each field contains half the information content, i.e., pixels, of the complete video frame. Note 2: Image flicker is less apparent in an interlaced display than in a noninterlaced display, because the rate at which successive fields occur in an interlaced display is twice that at which successive frames would occur in a noninterlaced display containing the same number of scanning lines and having the same frame refresh rate.

Inter-LATA - 1. Between local access and transport areas (LATAs). 2. Services, revenues, and functions associated with telecommunications that originate in one LATA and that terminate in another one or that terminate outside of that LATA.

InterLata Carrier - The carrier that provides your telecommunications service between your LATA and another LATA. Generally called "Long Distance Carriers."

Interleaving - The transmission of pulses from two or more digital sources in time-division sequence over a single path.

Interlocal Trunk - A circuit between two local central office units, either manual or dial. Interlocal trunks may be used for either exchange or toll traffic or both.

Intermediate Certificates - In cryptology, certificates in a certificate chain other than the first or end certificate.

Intermediate Distribution Frame (IDF) - In a central office or customer premises, a frame that (a) cross-connects the user cable media to individual user line circuits and (b) may serve as a distribution point for multipair cables from the main distribution frame (MDF) or combined distribution frame (CDF) to individual cables connected to equipment in areas remote from these frames.

Intermediate Element - In a network, a line-unit-line termination (LULT) or a line-unit-network termination (LUNT).

Intermediate Field - Synonym intermediate-field region.

Intermediate-Field Region - For an antenna, the transition region--lying between the near-field region and the far-field region--in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse square of the distance, and the inverse cube of the distance from the antenna. Note: For an antenna that is small compared to the wavelength in question, the intermediate-field region is considered to exist at all distances between 0.1 wavelength and 1.0 wavelength from the antenna. Synonyms intermediate field, intermediate zone, transition zone.

Intermediate Frequency (IF) - A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception.

Intermediate Language - In computer programming, a target language into which all or part of a single statement or a source program--in a source language--is translated before it is further translated or interpreted. Note: For a subsequent translation, an intermediate language may serve as a source language.

Intermediate-Level Language - In computer, communications, and data processing systems, a programming language that (a) is less machine-oriented than a machine language, (b) is not so machine-independent as a common language, such as Ada ®, COBOL, or Fortran, (c) contains macros that are less powerful than common-language macros, and (d) usually is the object language of a root compiler. Examples of intermediate-level languages include assembly languages, such as PL/I.

Intermediate Operating System - In some operating system (OS) architectures, the OS functions that may be implemented through a central element and one or more remote elements that may do such work as area resource control or area reports.

Intermediate System - A system that provides an Open Systems Interconnection--Reference Model (OSI--RM) Network Layer relay function in which data received from one corresponding network entity are forwarded to another corresponding network entity.

Intermediate Translation Signaling Point (ITSP) - A translation signaling point (TSP) that translates the global title (as received or after changing to another global title) to identify the next TSP in succession to which the switched control center system (SCCP) message is then routed. The next TSP may be another ITSP or a final TSP

Intermediate Trunk (IT) - A channel mapping designation that ranges between 1 and 216 and relates the digital circuit multiplication equipment (DCME) transmission trunk to an internal numbering designation used within the DCME for conveying trunk-channel-to-bearer-channel connectivity via the DCME assignment channel.

Intermediate Zone - Synonym intermediate-field region. For an antenna, the transition region--lying between the near-field region and the far-field region--in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse square of the distance, and the inverse cube of the distance from the antenna. Note: For an antenna that is small compared to the wavelength in question, the intermediate-field region is considered to exist at all distances between 0.1 wavelength and 1.0 wavelength from the antenna.

Intermittent Service Area - The area receiving service from the groundwave of a broadcast station but beyond the primary service area and subject to some interference and fading.

Intermodal Delay Distortion - Synonym multimode distortion. A distortion mechanism, occurring in multimode fibers, in which the signal is spread in time because the velocity of propagation of the optical signal is not the same for all modes. Note 1: In the ray-optics analogy, multimode distortion in a step-index optical fiber may be compared to multipath propagation of a radio signal. The direct signal is distorted by the arrival of the reflected signal a short time later. In a step-index optical fiber, rays taking more direct paths through the fiber core, i.e., those which undergo the fewest reflections at the core-cladding boundary, will traverse the length of the fiber sooner than those rays which undergo more reflections. This results in distortion of the signal. Note 2: Multimode distortion limits the bandwidth of multimode fibers. For example, a typical step-index fiber with a 50-m core would be limited to approximately 20 MHz for a one-kilometer length, i.e., a bandwidth of 20 MHz•km. Note 3: Multimode distortion may be considerably reduced, but never completely eliminated, by the use of a core having a graded refractive index. The bandwidth of a typical off-the-shelf graded-index multimode fiber, having a 50-m core, may approach 1 GHz•km or more. Multimode graded-index fibers having bandwidths approaching 3 GHz•km have been produced. Note 4: Because of its similarity to dispersion in its effect on the optical signal, multimode distortion is sometimes incorrectly referred to as " intermodal dispersion," " modal dispersion," or " multimode dispersion." Such usage is incorrect because multimode distortion is not a truly dispersive effect. Dispersion is a wavelength-dependant phenomenon, whereas multimode distortion may occur at a single wavelength.

Intermodal Dispersion - Incorrect synonym for multimode distortion.

Intermodal Distortion - Synonym multimode distortion.

Intermodulation (IM) - The production, in a nonlinear element of a system, of frequencies corresponding to the sum and difference frequencies of the fundamentals and harmonics thereof that are transmitted through the element.

Intermodulation Distortion (IMD) - Nonlinear distortion characterized by the appearance, in the output of a device, of frequencies that are linear combinations of the fundamental frequencies and all harmonics present in the input signals. Note: Harmonic components themselves are not usually considered to characterize intermodulation distortion. When the harmonics are included as part of the distortion, a statement to that effect should be made.

Intermodulation Noise - In a transmission path or device, noise, generated during modulation and demodulation, that results from nonlinear characteristics in the path or device.

Intermodulation Product - In the output of a nonlinear system, a frequency produced by intermodulation of harmonics of the frequencies present in the input signal.

Internal Bias - In a start-stop teletypewriter receiving mechanism, bias generated locally by the mechanism, and which has the same effect on the operating margin as bias external to the receiver, i.e., applied bias. Note: Internal bias may be a marking bias or a spacing bias.

Internal Call - A call placed within a private branch exchange (PBX) or local switchboard, i.e., not through a central office in a public switched network. Synonym inside call.

Internal Memory - In a computer, all of the storage spaces that are accessible by a processor without the use of the computer input-output channels. Note: Internal memory usually includes several types of storage, such as main storage, cache memory, and special registers, all of which can be directly accessed by the processor. Synonym internal storage.

Internal Photoelectric Effect - A photoconductive or photovoltaic effect.

Internal Storage - Synonym internal memory. In a computer, all of the storage spaces that are accessible by a processor without the use of the computer input-output channels. Note: Internal memory usually includes several types of storage, such as main storage, cache memory, and special registers, all of which can be directly accessed by the processor.

Internal VoIP - In a medium or large office, the internal phone system can be Internet based. In this case, calls between extensions, and possibly between office buildings, run over a private data network. To reach the outside world, the company's Internet phone system can connect to the Internet, the regular phone system, or both.

International Atomic Time (TAI) - The time scale established by the Bureau International des Poids et Mesures (BIPM--International Bureau of Weights and Measures in Sevres, France) on the basis of atomic clock data supplied by cooperating institutions.

International Carrier (INC) - A carrier authorized to provide telecommunications services outside World Zone 1 using the international dialing plan; however, the carrier has the option of providing service to World Zone 1 points outside the forty-eight contiguous states of the United States.

International Fixed Public Control Service - A fixed service carried on for the purpose of communicating between transmitting stations, receiving stations, message centers or control points in the international fixed public radiocommunication service.

International Fixed Public Radiocommunication Service - A fixed service, the stations of which are open to public correspondence and which, in general, is intended to provide radiocommunication between any one of the contiguous 48 states (including the District of Columbia) and the state of Alaska, or the State of Hawaii, or any U.S. possession or any foreign point; or between any U.S. possession and any other point; or between the state of Alaska and any other point; or between the state of Hawaii and any other point. In addition, radiocommunications within the contiguous 48 states (including the District of Columbia) in connection with the relaying of international traffic between stations which provide the above service, are also deemed to be the international fixed public radiocommunications service; provided, however, that communications solely between Alaska, or any one of the contiguous 48 states (including the District of Columbia), and either Canada or Mexico are not deemed to be in the international fixed public radiocommunication service when such radiocommunications are transmitted on frequencies above 72 MHz.

International Index Of Cooperation - Synonym index of cooperation. 1. In facsimile, the product of the total line length and the number of lines per unit length, divided by . 2. For rotating devices, the product of the drum diameter and the number of lines per unit length. Synonyms: diametral index of cooperation, international index of cooperation.

International Frequency Registration Board- See Radio Regulations Board. The Radio Regulations Board was formerly called International Frequency Registration Board (IFRB). A permanent organization of the International Telecommunication Union (ITU) that implements frequency assignment policy and maintains the Master International Frequency Register (MIFR). (IFRB).

International Organization for Standardization - See ISO. An international organization that (a) consists of member bodies that are the national standards bodies of most of the countries of the world, (b) is responsible for the development and publication of international standards in various technical fields, after developing a suitable consensus, (c) is affiliated with the United Nations, and (d) has its headquarters at 1, rue de Varembé, Geneva, Switzerland. Note: Member bodies of ISO include, among others, the American National Standards Institute (ANSI), the Association Française de Normalisation (AFNOR), the British Standards Institution (BSI), and the Deutsche Institut für Normung (DIN).

International Prefix - The combination of digits to be dialed by a calling subscriber making a call to a subscriber in another country to obtain access to the automatic outgoing international equipment.

International Radio Consultative Committee (CCIR) - See ITU-R. The Radiocommunications Sector of the ITU; responsible for studying technical issues related to radiocommunications, and having some regulatory powers. Note: A predecessor organization was the CCIR.

International Reference Alphabet (IRA) No. 5 - See ASCII. ASCII is an acronym for American Standard Code for Information Interchange, a code that represents the most basic letters of the Roman alphabet, numbers, and other characters used in computing. ASCII characters allow us to communicate with computers, which use their own language called binary made up of 0s and 1s. ASCII files are also called text files.

ASCII is the standard code used for information interchange among data processing systems, data communications systems, and associated equipment in the United States. Note 1: The ASCII character set contains 128 coded characters. Note 2: Each ASCII character is a 7-bit coded unique character; 8 bits when a parity check bit is included. Note 3: The ASCII character set consists of control characters and graphic characters. Note 4: When considered simply as a set of 128 unique bit patterns, or 256 with a parity bit, disassociated from the character equivalences in national implementations, the ASCII may be considered as an alphabet used in machine languages. Note 5: The ASCII is the U.S. version of International Reference Alphabet (IRA) No. 5 (formerly International Alphabet No. 5, or "IA5") as specified in ITU-T Recommendation T.50.

International Routing Code - A 3-digit code within the North American numbering plan, beginning with 1, that classifies international calls as requiring either regular or special handling.

International System of Units (SI) - The modern form of the metric system, which has been adopted by the United States and most other nations. Note: The SI is constructed from seven base units for independent physical quantities.

International Telecommunication Union (ITU) - A civil international organization established to promote standardized telecommunications on a worldwide basis. Note: The ITU-R and ITU-T are committees under the ITU. The ITU headquarters is located in Geneva, Switzerland. While older than the United Nations, it is recognized by the U.N. as the specialized agency for telecommunications.

International Telegraph Alphabet Number 5 (ITA-5) - An alphabet in which (a) 128 unique 7-bit strings are used to encode upper- and lower-case letters, 10 decimal numerals, special signs and symbols, diacritical marks, data delimiters, and transmission control characters, (b) 12 of the 7-bit strings are not assigned to any letter, numeral, or control character, and (c) the unassigned bit strings are open for use in a given country that may have unique requirements, such as monetary symbols; diacritical marks, such as the tilde, umlaut, circumflex, and dieresis, and (d) a two-condition 8-bit pattern may be used that consists of seven information bits and a parity check bit. Note: ITA-5 is used for effecting information interchange. It is a result of a joint agreement between the International Telegraph and Telephone Consultative Committee (CCITT), now ITU-T, of the International Telecommunication Union (ITU) and the International Organization for Standardization (ISO). It is published as CCITT (ITU-T) Recommendation V.3 and as ISO 646. It has also been adopted by NATO for military use. The United States adaptation of ITA-5 is ASCII (American Standard Code for Information Interchange) published by the American National Standards Institute (ANSI). Synonym International Reference Alphabet (IRA).

International Telegraph and Telephone Consultative Committee (CCITT) - See ITU-T. Abbreviation for International Telecommunication Union--Telecommunication Standardization Sector. The Telecommunication Standardization Sector of the International Telecommunication Union (ITU). Note 1: ITU-T is responsible for studying technical, operating, and tariff Questions and issuing Recommendations on them, with the goal of standardizing telecommunications worldwide. Note 2: In principle, the ITU-T combines the standards-setting activities of the predecessor organizations formerly called the International Telegraph and Telephone Consultative Committee (CCITT) and the International Radio Consultative Committee (CCIR).

International Time Bureau (BIH) - See International Atomic Time. The time scale established by the Bureau International des Poids et Mesures (BIPM--International Bureau of Weights and Measures in Sevres, France) on the basis of atomic clock data supplied by cooperating institutions.

Internaut - Slang term for a user of the Internet. Synonym cybernaut.

Internet - A collection and interconnection of tens of thousands of independent global networks.

internet - Any interconnection among or between private, industrial or governmental computer (digital communication) networks. Note: The term internet (spelled with a lower case "i") is distinguished from the Internet (spelled with the "I" capitalized). "The Internet" refers to a specific, historic, ubiquitous worldwide digital communications network.

Internet [the] - 1. A worldwide interconnection of individual networks a) with an agreement on how to talk to each other, and b) operated by government, industry, academia, and private parties. Note: The Internet originally served to interconnect laboratories engaged in government research, and has now been expanded to serve millions of users and a multitude of purposes, such as interpersonal messaging, computer conferences, file transfer, and consulting of files containing documents. 2. The international computer network of both federal and nonfederal interoperable packet switched data networks.

Internet2 - See I2. Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by government researchers and academic institutions.

Internet 2 - A proposed high-speed Internet for use exclusively by government researchers and academic institutions. See I2. Abbreviation for Internet second generation.

Internet Address - In The Internet protocol, the decimal-numeric, fixed-length address that identifies the hosts of data sources, and, specifically, a communication port. Note: A single Internet address can have multiple URLs. Synonyms IP address, Internet protocol address.

Internet Appliance - Synonym thin client. A server-centric computing model in which the application software, data, and CPU power resides on a network server rather than on the client computer (s). Note 1: This computing philosophy allows administrators to purchase one relatively powerful and expensive server and be confident that any external terminal, regardless of its power or sophistication, can run applications on the server. Most "shopping" Web pages, for example, are thin-client applications (i.e., the client needs nothing more than a browser and a connection to the network to be able to search the "shopping" page and to order products). Local area networks can use thin-client modeling to install only one copy of necessary programs onto the main server for many clients on the network to use. Note 2: Server software is required to interface clients with the software on the server. Synonyms Internet appliance (computing), Internet box (computing), network computer.

Internet Architecture Board (IAB) - The technical body that oversees the development of the Internet suite of protocols (commonly referred to as "TCP/IP "), and that has two task forces (the Internet Research Task Force and the Internet Engineering Task Force), each charged with investigating a particular field.

Internet Assigned Numbers Authority (IANA) - An organization, directed by the Internet Architecture Board, that assigns IP numbers and protocol parameters such as port, protocol, and enterprise numbers, and opinions, codes, and types.

Internet Control Message Protocol - See ICMP. An Internet protocol that reports datagram delivery errors. Note 1: ICMP is a key part of the TCP/IP protocol suite. Note 2: The packet internet gopher (ping) application is based on ICMP.

Internet Information Center - See InterNIC. The centralized organization run by the National Science Foundation that provides various administrative services for the Internet, including Domain Name registration.

Internet Mail Agent - Synonym message transfer agent. An OSI application process used to store and forward messages as described in the X.400 message handling system.

Internet Mall - Synonym cybermall. An electronic site shared by a number of commercial interests, and at which users can browse, shop, and place orders for the products listed at that site.

Internet Network Information Center - See InterNIC. The centralized organization run by the National Science Foundation that provides various administrative services for the Internet, including Domain Name registration.

Internet Phone - A combination of software and hardware that allows a user to approximate a telephone conversation over an Internet connection instead of using a traditional telephone system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of traditional telephone systems. Synonym Web phone.

Internet Phone Service - In the most flexible form of VoIP, Internet technology replaces the connection between the telephone and the phone company. You plug an ordinary telephone into an adapter that connects to your broadband setup. Your call is routed over the Web to a VoIP service provider. This provider connects your calls to the telephone system. If the person you are calling is also a user of the same Internet calling system, the call will never touch the phone system at all.

Internet Presence Provider - See IPP. An organization or commercial enterprise that provides storage space for the Web resources of an individual or other entity and enables those resources to be accessed by Internet users. Note: An IPP may not offer basic Internet connections as an ISP usually does.

Internet Protocol Address - Synonym Internet address. See IP address. A 32 bit address (four bytes separated by periods) that defines the location of a host on the Internet.

Internet Protocol (IP) - A DOD standard protocol designed for use in interconnected systems of packet-switched computer communication networks. Note: The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed-length addresses. The internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through small-packet networks.

Internet Protocol (IP) Spoofing - 1. The creation of IP packets with counterfeit (spoofed) IP source addresses. 2. A method of attack used by network intruders to defeat network security measures such as authentication based on IP addresses. Note 1: An attack using IP spoofing may lead to unauthorized user access, and possibly root access, on the targeted system. Note 2: A packet-filtering-router firewall may not provide adequate protection against IP spoofing attacks. It is possible to route packets through this type of firewall if the router is not configured to filter incoming packets having source addresses on the local domain. Note 3: IP spoofing is possible even if no reply packets can reach the attacker. Note 4: A method for preventing IP spoofing problems is to install a filtering router that does not allow incoming packets to have a source address different from the local domain. In addition, outgoing packets should not be allowed to contain a source address different from the local domain, in order to prevent an IP spoofing attack from originating from the local network.

Internet Relay Chat (IRC) - A popular program that allows users all around the world to communicate live, or chat, with other users. A service for conducting a chat on the Internet, i.e., an application that allows a number of individual users to exchange text messages simultaneously in real time over The Internet.

Internet Research Task Force - See IRTF. A task force of the Internet Architecture Board (IAB), and which is responsible for research and development of the Internet protocol suite.

Internet Resource - Within the Internet, an accessible facility or entity that contains information or provides data-processing capabilities. Note: An example of an Internet resource is a Web server.

Internet Search Engine - Synonym droid. - 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme.

Internet Service Provider - See ISP. A company or organization that provides connections to the Internet to companies or individuals via dial-up, ISDN, T1, or other connection.

Internet Society - See ISOC. A nongovernmental, international organization for global cooperation and coordination for The Internet and its internetworking technologies and applications.

Internet Telephone - See Internet phone. A combination of software and hardware that allows a user to approximate a telephone conversation over an Internet connection instead of using a traditional telephone system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of traditional telephone systems.

Internet Telephony - See Internet phone. See Internet phone. A combination of software and hardware that allows a user to approximate a telephone conversation over an Internet connection instead of using a traditional telephone system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of traditional telephone systems.

Internetwork - Synonym internet. 1. A worldwide interconnection of individual networks a) with an agreement on how to talk to each other, and b) operated by government, industry, academia, and private parties. Note: The Internet originally served to interconnect laboratories engaged in government research, and has now been expanded to serve millions of users and a multitude of purposes, such as interpersonal messaging, computer conferences, file transfer, and consulting of files containing documents. 2. The international computer network of both federal and nonfederal interoperable packet switched data networks.

Internetwork Connection - See gateway. 1. In a communications network, a network node equipped for interfacing with another network that uses different protocols. Note 1: A gateway may contain devices such as protocol translators, impedance matching devices, rate converters, fault isolators, or signal translators as necessary to provide system interoperability. It also requires that mutually acceptable administrative procedures be established between the two networks. Note 2: A protocol translation/mapping gateway interconnects networks with different network protocol technologies by performing the required protocol conversions. 2. [An] interface providing a compatibility between networks by converting transmission speeds, protocols, codes, or security measures. 3. Loosely, a computer configured to perform the tasks of a gateway.

Internetworking - The process of interconnecting two or more individual networks to facilitate communications among their respective nodes. Note: The interconnected networks may be different types. Each network is distinct, with its own addresses, internal protocols, access methods, and administration.

Iinternetwork Interface (INI) - The point of demarcation between networks when service is provided across multiple networks.

Internetwork Packet Exchange - See IPX. A proprietary (LAN) protocol.

InterNIC (Internet Network Information Center) - The centralized organization run by the National Science Foundation that provides various administrative services for the Internet, including Domain Name registration. The association of providers of domain-name registration, information, and database services to the Internet.

Interoffice Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between central offices.

Interoperability - 1. The ability of systems, units or forces to provide services to and accept services from other systems, units, or forces and to use the services so exchanged to enable them to operate effectively together. 2. The condition achieved among communications-electronics systems or items of communications-electronics equipment when information or services can be exchanged directly and satisfactorily between them and/or their users. The degree of interoperability should be defined when referring to specific cases. 3. Allows applications executing on separate hardware platforms, or in multi-processing environments on the same platform, to share data and cooperate in processing it through communications mechanisms such as remote procedure calls, transparent file access, etc. 4. The ability of a set of modeling and simulation to provide services to and accept services from other modeling and simulation, and to use the services for exchange enabling them to operate effectively together. 5. The capability to provide useful and cost-effective interchange of electronic data among, e.g., different signal formats, transmission media, applications, industries, or performance levels.

Interoperability Standard - A document that establishes engineering and technical requirements that are necessary to be employed in the design of systems, units, or forces and to use the services so exchanged to enable them to operate effectively together.

Interoperation - The use of interoperable systems, units, or forces.

Interpolation Gain - The input trunk channel multiplication ratio that is achieved through DSI. The interpolation gain is the ratio of the number of input transmission trunks to the number of DCME bearer channels where the same signal encoding rate is used for both trunk and bearer channels.

Interposition Trunk - 1. A single direct transmission channel, e.g., voice-frequency circuit, between two positions of a large switchboard to facilitate the interconnection of other circuits appearing at the respective switchboard positions. 2. Within a technical control facility, a single direct transmission circuit, between positions in a testboard or patch bay, which circuit facilitates testing or patching between the respective positions.

Interpret - To translate and to execute each source language statement of a computer program before translating and executing the next statement.

Interrogation - 1. The transmission of a signal or combination of signals intended to trigger a response. 2. The process whereby a station or device requests another station or device to identify itself or to give its status.

Interrupt - A suspension of a process, such as the execution of a computer program, caused by an event external to that process, and performed in such a way that the process can be resumed. Synonym interruption.

Interrupted Continuous Wave (ICW) - Modulation in which there is on-off keying of a continuous wave.

Interrupted Isochronous Transmission - Synonym isochronous burst transmission. In a data network where the information-bearer channel rate is higher than the input data signaling rate, transmission performed by interrupting, at controlled intervals, the data stream being transmitted. Note 1: Isochronous burst transmission enables communication between data terminal equipment (DTE) and data networks that operate at dissimilar data signaling rates, such as when the information-bearer channel rate is higher than the DTE output data signaling rate. Note 2: The binary digits are transferred at the information-bearer channel rate. The transfer is interrupted at intervals in order to produce the required average data signaling rate. Note 3: The interruption is always for an integral number of unit intervals. Note 4: Isochronous burst transmission has particular application where envelopes are being transferred between data circuit-terminating equipment (DCE) and only the bytes contained within the envelopes are being transferred between the DCE and the DTE.

Interruption - Synonym interrupt. A suspension of a process, such as the execution of a computer program, caused by an event external to that process, and performed in such a way that the process can be resumed.

Interruption Control - A system that monitors a pilot for interruptions on frequency division multiplexing (FDM) systems and that transmits an indication to the switching equipment.

Inter-Satellite Service - A radiocommunication service providing links between artificial Earth satellites.

Interswitch Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between switching nodes.

Intersymbol Interference - 1. In a digital transmission system, distortion of the received signal, which distortion is manifested in the temporal spreading and consequent overlap of individual pulses to the degree that the receiver cannot reliably distinguish between changes of state, i.e., between individual signal elements. Note 1: At a certain threshold, intersymbol interference will compromise the integrity of the received data. Note 2: Intersymbol interference attributable to the statistical nature of quantum mechanisms sets the fundamental limit to receiver sensitivity. Note 3: Intersymbol interference may be measured by eye patterns. 2. Extraneous energy from the signal in one or more keying intervals that interferes with the reception of the signal in another keying interval. 3. The disturbance caused by extraneous energy from the signal in one or more keying intervals that interferes with the reception of the signal in another keying interval.

Intertoll Circuits - Circuits between toll centers and circuits between a toll center and a tandem system in a different toll center area.

Intertoll Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between two toll offices.

Interworking Functions - Mechanisms that mask differences in physical, link, and network technologies by converting (or mapping) states and protocols into consistent network and user services.

IntraLATA - Telephone services within the boundaries of a local access area. See LATA. Generally known as "Local Telephone Companies."

Intra-LATA - Within the boundaries of a local access and transport area (LATA).

Intramodal Distortion - In an optical fiber, distortion caused by dispersion, such as material or profile dispersion, of a given propagating mode.

Intranet - Any private network that uses some or all of the protocols of The Internet. Note: In an intranet, nodes interact in a client-server relationship, nodes are identified by using Internet protocol (IP) addresses, and files are identified by universal resource locators (URLs). The data being exchanged are typically formatted using the HTML language, and is controlled and displayed using a browser. The intranet may be connected to The Internet via firewalls, or it may be totally separate.

Intraoffice Trunk - A single direct transmission channel, e.g., voice-frequency circuit, within a given switching center.

Intrinsic Joint Loss - Of nonidentical optical fibers joined by a splice or a mated pair of connectors, the power loss attributable to manufacturing variations, in such parameters as physical dimensions, differences in refractive index (including profile parameter), numerical aperture, and mode field diameter.

Intrinsic Noise - In a transmission path or device, that noise inherent to the path or device and not contingent upon modulation.

Intrusive Measurements - Measurements that require that the facility be taken out of service and made unavailable to the user.

Invalid Frame - A frame for which one or more of the following conditions apply: the frame is not properly bounded by flags; the frame does not consist of an integral number of octets prior to zero-bit insertion or following zero-bit extraction; the frame contains a frame-check sequence error (note that this condition is not recorded in the protocol abnormality log); the frame contains an incorrect address field.

Inverse Adaptive Quantizer - In the encoder and the feedback path of the decoder, the process that maps the core bits into a quantized difference signal. In the feed-forward path of the decoder, the process that maps the core bits and the received enhancement bits into a quantized difference signal

Inverse Multiplexer - A functional unit capable of accessing and combining two or more low-speed circuits into a virtual broadband circuit, up to and including an aggregate equal to a T1 rate.

Inverse-Square Law - The physical law stating that irradiance, i.e., the power per unit area in the direction of propagation, of a spherical wavefront varies inversely as the square of the distance from the source, assuming there are no losses caused by absorption or scattering. Note: For example, the power radiated from a point source, e.g., an omnidirectional isotropic antenna, or from any source at very large distances from the source compared to the size of the source, must spread itself over larger and larger spherical surfaces as the distance from the source increases. Diffuse and incoherent radiation are similarly affected.

Inverted Position - In frequency-division multiplexing, a position of a translated channel in which an increasing signal frequency in the untranslated channel causes a decreasing signal frequency in the translated channel.

Inverter - 1. In electrical engineering, a device for converting direct current into alternating current. 2. In computers, a device or circuit that inverts the polarity of a signal or pulse. Deprecated synonym negation circuit.

Inward Wide-Area Telephone Service (INWATS) - Synonym eight-hundred (800) service. A service that allows call originators to place toll telephone calls to 800-service subscribers, from within specified rate areas, without a charge to the call originator. Note: The 800 series denotes the service access codes of 800, 888, 877, 866, 855, 844, 833, and 822.

INWATS - Acronym for Inward Wide-Area Telephone Service. Synonym eight-hundred (800) service. A service that allows call originators to place toll telephone calls to 800-service subscribers, from within specified rate areas, without a charge to the call originator. Note: The 800 series denotes the service access codes of 800, 888, 877, 866, 855, 844, 833, and 822.

I/O - Abbreviation for input / output.

IONL - Abbreviation for Internal Organization of the Network Layer. The OSI standard for the detailed architecture of the Network Layer. Note: Basically, it partitions the Network layer into subnetworks interconnected by convergence protocols (equivalent to internetworking protocols), creating what is called a catenet or internet.

Ionosphere - That part of the atmosphere, extending from about 70 to 500 kilometers, in which ions and free electrons exist in sufficient quantities to reflect and/or refract electromagnetic waves.

Ionosphere Sounder - A device that transmits signals for the purpose of determining ionospheric conditions.

Ionospheric Absorption - Absorption occurring as a result of interaction between an electromagnetic wave and free electrons in the ionosphere.

Ionospheric Disturbance - An increase in the ionization of the ionosphere, caused by solar activity, which results in greatly increased radio wave absorption.

Ionospheric Forward Scatter (IFS): Synonym ionospheric scatter. The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere.

Ionospheric Reflection - Of electromagnetic waves propagating in the ionosphere, a redirection, i.e., bending--by a complex processing involving reflection and refraction--of the waves back toward the Earth. Note: The amount of bending depends on the extent of penetration (which is a function of frequency), the angle of incidence, polarization of the wave, and ionospheric conditions, such as the ionization density.

Ionospheric Scatter - The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere. Synonym forward propagation ionospheric scatter

Ionospheric Sounding - A technique that provides real-time data on high-frequency ionospheric-dependent radio propagation, using a basic system consisting of a synchronized transmitter and receiver. Note: The time delay between transmission and reception is translated into effective ionospheric layer altitude. Vertical incident sounding uses a collocated transmitter and receiver and involves directing a range of frequencies vertically to the ionosphere and measuring the values of the reflected returned signals to determine the effective ionosphere layer altitude. This technique is also used to determine the critical frequency. Oblique sounders use a transmitter at one end of a given propagation path, and a synchronized receiver, usually with an oscilloscope-type display (ionogram), at the other end. The transmitter emits a stepped- or swept-frequency signal which is displayed or measured at the receiver. The measurement converts time delay to effective altitude of the ionospheric layer. The ionogram display shows the effective altitude of the ionospheric layer as a function of frequency.

Ionospheric Turbulence - Ongoing disturbances of the ionosphere that scatter incident electromagnetic waves. Note: Ionospheric turbulence results in irregularities in the composition of the ionosphere that change with time. This causes changes in reflection properties. These, in turn, cause changes in skip distance, fading, local intensification, and distortion of the incident waves.

IP - Abbreviation for intelligent peripheral, Internet protocol. A DOD standard protocol designed for use in interconnected systems of packet-switched computer communication networks. Note: The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed-length addresses. The internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through small-packet networks.

IP Address - A 32 bit address (four bytes separated by periods) that defines the location of a host on the Internet. A device's or resource's numerical address as expressed in the format specified in the Internet Protocol. Note 1: In the current addressing format, IP version 4 (IPv4), an IP address is a 32-bit sequence divided into four groups of decimal numbers separated by periods ("dots"), commonly referred to as "dotted decimals." The IP address of a device is made up of two parts: the number of the network to which it is connected, and a sequence representing the specific device within that network. An IP address may be used on private intranets, as well as The Internet. Note 2: Due to inefficiencies that have arisen in address assignment, available IPv4 addresses are nearly exhausted. A newer version of IP addressing (IP version 6, consisting of a 128-bit numerical sequence) is currently being developed. Synonyms Internet address, IP number.

IPC - Abbreviation for information processing center. A facility staffed and equipped for processing and distributing information. Note: An IPC may be geographically distributed.

IP Datagram - The fundamental unit of information passed across any network utilizing Internet protocol. Note: An IP datagram contains source and destination addresses along with data and a number of fields that define such things as the length of the datagram, the header checksum, and flags that indicate whether the datagram can be (or has been) fragmented.

IP Dialup Access - Nonpermanent access, by means of a switched network (e.g., the public switched telephone network), to any network utilizing The Internet Protocol, especially The Internet. Note: Two well-known protocols for dialup access are PPP (point-to-point) and SLIP (serial line internet protocol).

IP Multicast - A technique that allows packets to be simultaneously transmitted over the Mbone (multicast backbone on The Internet) to a selected set of destinations. Note: Standard Internet traffic requires a separate set of packets for each destination. IP multicast allows for one set of packets to be sent to multiple destinations.

IPng - Abbreviation for IP next generation, IP version 6.

IP number - Synonym IP address. A device's or resource's numerical address as expressed in the format specified in the Internet Protocol. Note 1: In the current addressing format, IP version 4 (IPv4), an IP address is a 32-bit sequence divided into four groups of decimal numbers separated by periods ("dots"), commonly referred to as "dotted decimals." The IP address of a device is made up of two parts: the number of the network to which it is connected, and a sequence representing the specific device within that network. An IP address may be used on private intranets, as well as The Internet. Note 2: Due to inefficiencies that have arisen in address assignment, available IPv4 addresses are nearly exhausted. A newer version of IP addressing (IP version 6, consisting of a 128-bit numerical sequence) is currently being developed.

IPP - Abbreviation for Internet presence provider. An organization or commercial enterprise that provides storage space for the Web resources of an individual or other entity and enables those resources to be accessed by Internet users. Note: An IPP may not offer basic Internet connections as an ISP usually does.

IP Spoofing - 1. A technique used by hackers to access computer systems by modifying packet headers to make them appear to have originated from a trusted port. 2. The practice of falsifying an e-mail header to make it appear as though it originated from a different address.

IP Switching - A method of routing developed to use asynchronous transfer mode (ATM) hardware to route packets through networks more rapidly.

IPTF - Abbreviation for Infrastructure Protection Task Force. Preemptive or reactive risk-management techniques designed to prevent disruption of a system after its critical infrastructure is attacked.

IPX - Abbreviation for Internetwork Packet Exchange. A proprietary (LAN) protocol.

IR - Abbreviation for infrared. The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (approximately 0.7 m) and the shortest microwaves (approximately 0.1 mm).

IRC - See Internet Relay Chat. - A popular program that allows users all around the world to communicate live, or chat, with other users. A service for conducting a chat on the Internet, i.e., an application that allows a number of individual users to exchange text messages simultaneously in real time over The Internet.

Irradiance - Radiant power incident per unit area upon a surface. Note: Irradiance is usually expressed in watts per square meter, but may also be expressed in joules per square meter. Deprecated synonym power density.

Irradiation - The product of irradiance and time, i.e., the time integral of irradiance. Note: For example, an irradiation of 100 J/m² (joules per square meter) is obtained when an irradiance of 25 W/m²(watts per square meter) is continuously incident for 4 seconds.

Irreversible Encryption - Encryption that produces ciphertext from which the original data cannot be reproduced. Note: Irreversible encryption is useful in authentication. For example, a password might be irreversibly encrypted and the resulting ciphertext stored. A password presented later would be irreversibly encrypted identically and the two strings of ciphertext compared. If they are identical, the presented password is correct. Synonyms irreversible encipherment, one-way encryption.

IRTF - Abbreviation for Internet Research Task Force. A task force of the Internet Architecture Board (IAB), and which is responsible for research and development of the Internet protocol suite.

ISB - Abbreviation for independent sideband. See independent-sideband transmission. Double-sideband transmission in which the information carried by each sideband is different. Note: The carrier may be suppressed.

ISDN - See Integrated Services Digital Network - ISBDN usually refers to Broadband Integrated Services Digital Network or B-ISDN. The main aspect of BISDN that has been developed and published as a standard is the use of ATM multiplexing and routing for high bit-rate data services; BISDN refers to use of ATM. BISDN appears to have very little relationship to ordinary (circuit-switched 64 kb/s channel) ISDN systems, although there are some so-called "broadband" or "wideband" ISDN circuit switched services such as 384 kbit/s (sometimes called a "six-pack" because it uses six channels of 64 kb/s each). An integrated digital network in which the same time-division switches and digital transmission paths are used to establish connections for different services. Note 1: ISDN services include telephone, data, electronic mail, and facsimile. Note 2: The method used to accomplish a connection is often specified: for example, switched connection, nonswitched connection, exchange connection, ISDN connection.

ISDN User Part (ISUP) - The functional part of the Signaling System No. 7 (SS7) protocol, i.e., the part that specifies the interexchange signaling procedures for the set up and tear down of trunk calls between networks. The ISDN User Part is one of the specified users of the Message Transfer Part (MTP) transport capability of the SS7 interconnections. The user part identification is encoded in the service indicator (SI) portion of the service information octet (SIO).

ISM - Abbreviation for industrial, scientific, and medical applications (of radio frequency energy).

ISMAP - A Web page feature in which hyperlinks are assigned or "mapped" to different portions of a graphic image. Note: Users access links by using a mouse to click on mapped areas. ISMAP requests are processed by common gateway interface (CGI) scripts on the server.

ISO - Abbreviation for International Organization for Standardization. An international organization that (a) consists of member bodies that are the national standards bodies of most of the countries of the world, (b) is responsible for the development and publication of international standards in various technical fields, after developing a suitable consensus, (c) is affiliated with the United Nations, and (d) has its headquarters at 1, rue de Varembé, Geneva, Switzerland. Note: Member bodies of ISO include, among others, the American National Standards Institute (ANSI), the Association Française de Normalisation (AFNOR), the British Standards Institution (BSI), and the Deutsche Institut für Normung (DIN).

ISOC - Abbreviation for Internet Society. A nongovernmental, international organization for global cooperation and coordination for The Internet and its internetworking technologies and applications.

Isochrone - A line on a map or chart joining points associated with a constant time difference from the transmitter to receiver of electromagnetic waves, such as radio waves, at all points along the line.

Isochronous - 1. Of a periodic signal, pertaining to transmission in which the time interval separating any two corresponding transitions is equal to the unit interval or to a multiple of the unit interval. 2. Pertaining to data transmission in which corresponding significant instants of two or more sequential signals have a constant phase relationship. Note: "Isochronous" and "anisochronous" are characteristics, while "synchronous" and "asynchronous" are relationships.

Isochronous Burst Transmission - In a data network where the information-bearer channel rate is higher than the input data signaling rate, transmission performed by interrupting, at controlled intervals, the data stream being transmitted. Note 1: Isochronous burst transmission enables communication between data terminal equipment (DTE) and data networks that operate at dissimilar data signaling rates, such as when the information-bearer channel rate is higher than the DTE output data signaling rate. Note 2: The binary digits are transferred at the information-bearer channel rate. The transfer is interrupted at intervals in order to produce the required average data signaling rate. Note 3: The interruption is always for an integral number of unit intervals. Note 4: Isochronous burst transmission has particular application where envelopes are being transferred between data circuit-terminating equipment (DCE) and only the bytes contained within the envelopes are being transferred between the DCE and the DTE. Synonyms burst isochronous (deprecated), interrupted isochronous transmission.

Isochronous Demodulation - Demodulation in which the time interval separating any two significant instants is equal to the unit interval or a multiple of the unit interval.

Isochronous Distortion - The difference between the measured modulation rate and the theoretical modulation rate in a digital system.

Isochronous Modulation - Modulation in which the time interval separating any two significant instants is equal to the unit interval or a multiple of the unit interval.

Isochronous Signal - A signal in which the time interval separating any two significant instants is equal to the unit interval or a multiple of the unit interval. Note 1: Variations in the time intervals are constrained within specified limits. Note 2: "Isochronous" is a characteristic, while "synchronous" indicates a relationship.

Isolate - To restrict communication in both directions with a participant of the conference.

Isolated Bonding Network - Synonym isolated ground plane. A set of interconnected frames that is intentionally grounded via only one connection to a ground reference; this plane, taken as a conductive unit with all of its metallic surfaces and grounding (earthing) wires bonded together, is insulated from contact with any other grounded metalwork in the building.

Isolated Ground Plane - A set of interconnected frames that is intentionally grounded via only one connection to a ground reference; this plane, taken as a conductive unit with all of its metallic surfaces and grounding (earthing) wires bonded together, is insulated from contact with any other grounded metalwork in the building. Synonym isolated bonding network.

Isolated NRZ Pulse - A single bit period of logical value "1" with adjacent bit periods of logical value "0".

Isolated Pulse - A pulse free from the effects of the other pulses in the same signal. (A suitable testing signal is a repetitive pattern of one "one" and seven "zeros".)

Isolated RZ Pulse - Any bit period of logical value "1."

Isolator - See optical isolator. A device that uses a short optical transmission path to accomplish electrical isolation between elements of a circuit. Note 1: The optical path may be air or a dielectric waveguide. Note 2: The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, e.g., on a circuit board.

Isotropic - 1. Pertaining to a material with properties, such as density, electrical conductivity, electric permittivity, magnetic permeability, or refractive index that do not vary with distance or direction. 2. Pertaining to a material with magnetic, electrical, or electromagnetic properties that do not vary with the direction of static or propagating magnetic, electrical, or electromagnetic fields within the material.

Isotropic Antenna - A hypothetical antenna that radiates or receives equally in all directions. Note: Isotropic antennas do not exist physically but represent convenient reference antennas for expressing directional properties of physical antennas.

Isotropic Gain - Synonym absolute gain. 1. Of an antenna, for a given direction and polarization, the ratio of (a) the power that would be required at the input of an ideal isotropic radiator to (b) the power actually supplied to the given antenna, to produce the same radiation intensity in the far-field region. Note 1: If no direction is given, the absolute gain of an antenna corresponds to the direction of maximum effective radiated power. Note 2: Absolute gain is usually expressed in dB. 2. Of a device, the ratio of (a) the signal level at the output of the device to (b) that of its input under a specified set of operating conditions. Note 1: Examples of absolute gain are no-load gain, full-load gain, and small-signal gain. Note 2: Absolute gain is usually expressed in dB.

ISP - Abbreviation for Internet Service Provider. A company that provides connection to the Internet to companies or individuals via dial-up, ISDN, T1, or other connection.

I2 - Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by government researchers and academic institutions.

IT - Abbreviation for information technology. The branch of technology devoted to (a) the study and application of data and the processing thereof; i.e., the automatic acquisition, storage, manipulation (including transformation), management, movement, control, display, switching, interchange, transmission or reception of data, and (b) the development and use of the hardware, software, firmware, and procedures associated with this processing.

Iterative Impedance - In electrical circuits, for a four-terminal network, the impedance that, if connected across one pair of terminals, will match the impedance across the other pair of terminals. Note: The iterative impedance of a uniform line is the same as its characteristic impedance.

ITU - Abbreviation for International Telecommunication Union. A civil international organization established to promote standardized telecommunications on a worldwide basis. Note: The ITU-R and ITU-T are committees under the ITU. The ITU headquarters is located in Geneva, Switzerland. While older than the United Nations, it is recognized by the U.N. as the specialized agency for telecommunications.

ITU-R - The Radiocommunications Sector of the ITU; responsible for studying technical issues related to radiocommunications, and having some regulatory powers. Note: A predecessor organization was the CCIR.

ITU-T - Abbreviation for International Telecommunication Union--Telecommunication Standardization Sector. The Telecommunication Standardization Sector of the International Telecommunication Union (ITU). Note 1: ITU-T is responsible for studying technical, operating, and tariff Questions and issuing Recommendations on them, with the goal of standardizing telecommunications worldwide. Note 2: In principle, the ITU-T combines the standards-setting activities of the predecessor organizations formerly called the International Telegraph and Telephone Consultative Committee (CCITT) and the International Radio Consultative Committee (CCIR).

IVDT - Abbreviation for integrated voice data terminal. See integrated station.

IXC - Abbreviation for interexchange carrier. 1. A communications common carrier authorized to provide interexchange telecommunications services within world zone 1 using the North American numbering plan. 2. A telecommunications common carrier authorized to provide telecommunications services between LATAs. Note: The term "interexchange carrier" is also used to refer to any other entity that connects to the exchange access network at a point of termination (POT). 3. A carrier that provides connections between LATAs, where the calling or called customer is located in the United States. Note: This definition has no Canadian equivalent. However, the term "interexchange carrier" is used in the context of a carrier that provides connections extending across borders to carriers in the United States.

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