Telos NX12 user manual Listed Directory Number- See LDN

guide to telephone terminology  109

LEC- Local Exchange Carrier. Your local telephone service pro- vider 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. An electrical connection between a telephone service provider’s switch and another switch is technically called a trunk. Note that some type of physical lines offer more than one channel. I.E. a BRI circuit 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 con- nected. 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 average density of 12.5% ones must be main- tained. The CSU is responsible to ensure that these requirements are met. The line encoding method, 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 Echo Canceller (LEC)- When a two-way digital path is interfaced to an analog line, echoes result from the leakage of the send audio into the receive. When combined with delay, these are annoying and can disrupt conversation. An LEC works to remove these echoes, usually using an adaptive digital filter. See Hybrid.

Line Encoding, T1- See Line Coding, T1.

Line Format, T1-Modern T1 circuits usually use either Super- frame (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 that the subscriber’s telephone lines are connected to. 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. 2) The user side of a PBX. Also called the station side.

Line Termination - See LT.

Local Access and Transport Area- See LATA.

Local Exchange Carrier- See LEC and CLEC.

Long Distance- If your local 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. 2) However, under the current state of deregulation, toll calls within a LATA may now be covered by the IEC, and in some cases RBOCs are being permitted to handle InterLATA calls.

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

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

Loop Qualification- 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 determin- ing factor whether ISDN service can be offered without a repeater. Generally ISDN 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 termi- nal 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. See Loop Start Line. 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. See Ground Start Trunk. See also Glare. The Telco may call this a “Loop Start Line”.

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.

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- Company which now makes the former AT&T 5ESS switch, as well as various other piece of Telco gear and semiconductors. Lucent was split off from AT&T in 1996. As of approximately 1999 Lucent sold their telephone set manufacturing business (and the right to use the AT&T name on telephone sets) to V-Tech. V-Tech is using the AT&T name and line as their high- end line. Lucent’s PBX division was spun off in 2001 as AVAYA.

MCLD- Modifying Calling Line Disconnect. The parameter on the Lucent 5ESS switch that determines if CPC is active. Should be set to “Yes” if CPC is required. See CPC

MOS Grade- “Mean Opinion Score” Grade is a measure of codec quality, ranging from 1 to 5. These are derived from subjective tests with listening panels comprised of both experts and “people from