Telecom Dictionary

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I-MAC 
isonchronous media access controller

IDN 
integrated digital network

IEC 
International Electrotechnical Commission

Impairments
Impairments is the (e.g., transmission channel and signal impairments) degradation caused by 
practical limitations of channels, (e.g., signal level loss or attenuation, echo, various types of 
signal distortion, etc.) or interference induced from outside the channel (such as power-line hum 
or interference from heavy electrical machinery). The measurement of transmission impairments 
is an important aspect of predicting whether or not telecommunications systems will sustain the 
business applications they are intended to support. Signal-to-noise ratio, percent distortion, 
frequency response, and echo are measurements that define impairments most noticeable by 
users in analog voice systems.

Inbound Signaling
Inbound signaling uses not only the same channel path as the voice traffic, but the same 
frequency range (band) used for the voice traffic.

Independent Telephone Company (ITC)
ITC is a local exchange carrier that is not one of the 22 divested Bell-operating companies. ITCs 
are not generally subject to the restrictions of the MFJ, although some of the larger ones are 
bound by separate consent decrees. Southern New England Telephone and Cincinnati Bell are 
generally considered ITCs from a regulatory point of view.

Integrated Services Digital Network (ISDN)
ISDN consists of a set of standards being developed by the CCITT and various U.S. standards 
setting organizations. The CCITT formal recommendations, adopted in October, 1984, first 
defined ISDN as ". . . a network, in general evolving from a telephony integrated digital network, 
that provides end-to-end digital connectivity to support a wide range of services, including voice 
and non-voice, to which users will have access by a limited set of standard multipurpose user-
network interfaces." The concept of user access to an existing integrated digital network (IDN) 
underlies the ISDN.

Inter-LATA Services
Inter-LATA services are revenues, functions, etc., that relate to telecommunications originating in 
one LATA and terminating outside that LATA. An interexchange carrier (IXC) is a company which 
provides telecommunications services between LATAs. (the domain of IXCs).

Intermediate Cross Connects
In a premises distribution system, intermediate cross connects are cross-connects located 
telecommunications closets.

International Organization for Standardization (ISO)
ISO is a worldwide federation of national standards bodies (ISO National Bodies). The work of 
preparing international standards is normally carried out through ISO technical committees. Draft 
proposals for international standards adopted by the technical committees are circulated to the 
National Bodies for approval before their acceptance as Draft International Standards by the 
committee.

Internet
The internet is a large collection of connected networks, primarily in the United States, running 
the Internet suite of protocols. Sometimes referred to as the DARPA Internet, NSF/DARPA In 
ternet, or the Federal Research Network.

Internet suite of protocols
The internet suite of protocols is a collection of computer-communication protocols originally 
developed under DARPA sponsorship, including the transmission control protocol/internet 
protocol (TCP/IP).

Interoffice Channel
In LEC tariffs, Interoffice Channel is the channel connecting two serving COs (more accurately 
serving wire centers). In IXC tariffs, the channel connecting two serving IXC POPs, interoffice 
transmission facilities used to connect LEC switching systems.

Intra-LATA
Intra-LATA are services, revenues, functions, etc., that relate to telecommunications originating 
and terminating within a single LATA (the domain of LECs).

IOC 
interoffice channel

IPX 
internetwork packet exchange

IP 
internet protocol

ISDN 
integrated services digital network

Isochronous Signals
Isochronous Signals are periodic signals in which the time interval that separates any two 
corresponding significant occurrences or level transitions is always equal to some unit interval or 
a multiple of that unit interval. For example, in digitized voice signals, ideally voice samples occur 
isochronously at precisely the sampling interval or frame rate. Packet data signals are not 
isochronous.

ISO 
International Organization for Standardization

ITC 
independent telephone company

ITU 
International Telecommunications Union

IVR 
integrated voice response