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, frequencyresponse, 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

　　internetworkpacket 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 correspondingsignificant 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

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

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

　　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.

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

　　Internet Relay Chat (IRC) - A popular program that allows users all around the world to communicate live, or chat, with other users.

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

　　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.

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

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

　　IRC - See Internet Relay Chat

　　ISDN - See Integrated Services Digital Network

　　ISP - Internet Service Provider. A company that provides connection to the Internet.
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