Telephone Terminology I-L

I

IEC - Inter-Exchange Carrier. “Long Distance” carrier. Handles InterLATA and interstate calls. Most often referred to as IXC.

IEC - International Electrotechnical Committee. A European standards body best known for the power plug now used throughout the world for AC power cords on office equipment and computers.

ILEC – Incumbent Local Exchange Carrier. A local Exchange Carrier that entered the marketplace before the enactment of the 1996 Telecom act, i.e. a telephone company which is neither an Independent nor an RBOC. See LEC and CLEC.

IMUX – See Inverse Multiplexing.

In Band Signaling- A signaling system where network information such as address and routing information are handled over the communications (voice) path itself. Usually the information is represented in the form of audible tones, however DC loop current signaling also qualifies as In Band Signaling. See also CCIS.

Incumbent Local Exchange Carrier - See ILEC. See also CLEC & LEC

Independent – Any of the phone companies in existence at the time of divestiture that were not affiliated with the Bell System. See RBOC, LEC, and CLEC.

Indi - See Independent.

Interconnect Company - A vendor of telecommunications CPE other than a BOC or AT&T. This term was originated by AT&T and was meant to be derisive towards the fledgling industry when the courts said it was OK for end users to buy equipment from someone other than the Bell System. This industry flourished, in spite of AT&T’s disdain, and ironically, the RBOCs were not allowed to sell CPE under the terms of the break up of AT&T. With the current state of deregulation, the RBOCs are slowly re-entering this business. The term is now considered archaic at the time of this writing.

Inter-exchange Carrier - See IEC.

Interwork - The ability of two different type of networks to communicate seamlessly. For example, ISDN can interwork calls to both a POTS network and a Switched-56 network.

ISDN - Integrated Services Digital Network. A relatively new and highly flexible type of telephone service which allows dialing on digital channels with multiple bi-directional “bearer” channels each with a capacity of 56 or 64 Kbps and a single bi-directional “D channel”. See BRI and PRI.

ISDN Protocol - The “language” used for communication between the Telco’s switch and the customer’s Terminal Adapter. Each ISDN circuit has one protocol, and the protocol has no effect on where or whom one may call. See ETS 300, National ISDN, and Custom ISDN.

ISDN 2 - A term used in Europe for ISDN BRI. Also called SØ. Not to be confused with National ISDN-2. See BRI.

ISDN 30 - A term used in Europe for ISDN PRI. Also called S2M. See PRI.

ISG – Incoming Service Grouping. A Hunt Group. See Hunt Group.

IXC - IntereXchange Carrier. See IEC.

K

Kbps - KiloBits Per Second. Measure of digital channel capacity.

Key Telephone System – A system that allows multiple telephones to share multiple pre-determined telephone lines. The system provides indicators to allow the user’s to understand the status of each line available on a given phone. In its most basic form it is up to the user to provide the intelligence to select an unused line, or answer a ringing line, for example. See also PBX.

L

LATA- Local Access and Transport Area. The area within which calls are routed by your Local Exchange Carrier (LEC). Under the divestiture of the Bell System, calls going outside of this area must be handled by an Interexchange carrier (IEC). With the latest round of de-regulation the usual IEC companies are being allowed to compete in the IntraLATA long-distance market and LECs are beginning to be permitted to handle InterLATA calls.

LDN - Listed Directory Number. When a number of Telco channels share the same hunt group, it is customary to give out only one phone number for the group although generally, each channel will have its own number. The number given out is the “Listed Directory Number” since that is the number that would be listed in the Telephone Directory and given to customers. Sometimes called a Pilot Number. See also DN and Hunt Group.

LE - Local Exchange. European term for Central Office. See CO.

LEC- Local Exchange Carrier. Your local telephone service provider which is either an RBOC or an Independent. In other words, a traditional phone company. In contrast to CLEC or IEC.

Line - An electrical connection between a telephone service provider’s switch (LEC or CLEC) and a telephone terminal or Key system. In contrast to a Trunk, which is an electrical connection between a telephone service provider’s switch and another switch. Note that some types of physical lines offer more than one channel such as a BRI circuit which has 2 channels, called B channels. This term is a confusing one, so we try to avoid using it. See Channel. See also Station Line.

Line Card - The circuit in the Telco switch to which your line is connected. On an ISDN circuit, the line card performs a role analogous to the NT1 in adapting to and equalizing the circuit to establish OSI Layer 1.

Line Coding, T1 - The clock signal for T1 is derived at the far end from the data bits themselves. Therefore, T1 lines have certain restrictions as to the data allowed. No more than 15 zeros shall be sent in a row, and an average density of 12.5% ones must be maintained. The CSU is responsible to ensure these requirements are met. The line encoding method, either AMI or B8ZS, determines exactly how these requirements are met while still allowing recovery of the original data at the far end. Your Telco will determine the method used on a specific circuit. B8ZS is preferred. E1 circuits have similar restrictions. HDB3 is preferred for E1 circuits.

Listed Directory Number - See LDN.

Line Equipment – The circuit on a telephone company’s switch that is used to provide service to a customer.

Line Encoding, T1 - See Line Coding, T1.

Line Format, T1 - Modern T1 circuits usually use either Superframe (sometimes called SF or D4) or Extended Superframe (sometimes called ESF) line formatting. The type of framing used is determined by your Telco. ESF is preferred. See ESF and SF.

Line Side - This is the side of a central office switch to which the subscriber’s telephone lines are connected, i.e., the user side of a PBX. Also called the Station Side. The main reason for distinguishing between this and the trunk side is that certain customer related features (Such as CLASS and Centrex features) are inapplicable to trunks. See also Trunk Side.

Line Termination - See LT.

Local Access and Transport Area - See LATA.

Local Exchange Carrier - See LEC and CLEC.

Long Distance - If your local U.S. Telco is a former Bell Operating Company, then any call outside of your LATA or any Interstate call is considered long distance and is handled by an IEC. The above is true regardless of whether you are referring to a dedicated line or a dial-up call. However, under the current state of deregulation, toll calls within a LATA may now be covered by the IXC, and in some cases RBOCs are being permitted to handle InterLATA calls. These requirements are largely ignored at the time of this writing.

Loop - The telephone circuit from the CO to the customers premises. Generally refers to a copper cable circuit.

Loop Current Disconnect Supervision - Another name for CPC. See CPC.

Loop Qualification - The process of actually measuring the loss on a prospective ISDN line to see if it can be used for ISDN service. The actual loss on the line (usually measured at 40 kHz) is the determining factor as to whether ISDN service can be offered without a repeater. Generally, ISDN or DSL is available up to 18,000 feet from the serving Central Office. It may not be available within this range, or may be available further from the CO. Only a loop qualification can tell for sure. Not all Telcos will extend ISDN lines with repeaters.

Loop Start Line - A plain old telephone line. The telephone terminal signals the “off hook” condition by allowing DC current to flow. See Ground Start Trunk. See also Glare.

Loop Start Trunk – A plain old telephone line connected to a PBX switch. The PBX signals the “off hook” condition by allowing DC current to flow. Ground Start Trunks are generally preferred for use on PBXs to prevent glare. Also, most trunks are considered “designed circuits” which means that only a specified amount of loop loss is permissible, and the telephone company is required to deliver the trunk to the customer at a given audio level. At the time of this writing, analog trunks are rapidly becoming less common as they are expensive to design, provision and maintain. See Loop Start Line. See also Ground Start Trunk. See also Glare.

LOS - Loss Of Signal. An LED or other indicator that illuminates if a signal is absent. This terminology is commonly used with T-1 equipment. See Red Alarm.

LT - Line Termination. The electrical and protocol specifications for the Central Office end of an ISDN line. If you wish to connect an ISDN terminal (such as a Zephyr Xstream) to a PBX, the PBX must support LT ISDN. See also NT and Line Card.

Lucent Technologies - The company that made the former AT&T 5ESS switch as well as various other pieces of Telco gear and semiconductors. Lucent was split off from AT&T in 1996. Lucent’s PBX division was spun off in 2001 as AVAYA.