Another name for a Central Office. See CO
A circuit path using separate pairs for send and receive. This term is also used when referring to digital channels that inherently have discrete send and receive paths, regardless of the number of pairs (or other media) used.
A unit of data which is defined by the specific communications protocol used. See Line Format, T1.
On a POTS line an incoming call is signaled by periodically applying an AC ring voltage to the line. Since there is a semi random period before the ring, and pauses between rings, it is possible to seize a line which is "about to ring" (and answer a call) when attempting to place an outgoing call. When this scenario happens it is called glare. Glare is much less likely if Ground Start trunks are used. See Ground Start Trunk.
Grade Of Service
This is simply the ratio of calls blocked to total calls in a decimal form. So a grade of service of P.08 would represent 8% blocking. Telephone tariffs regulate the acceptable average grade of service which must be provided on public networks.
Ground Start Trunk
A type of telephone trunk where the request to make an outgoing call (i.e. request for dial tone) is made by briefly grounding the Tip conductor. Many PBX systems use ground start trunks as they are less prone to glare than Loop start trunks. See Loop Start Trunk. See also Glare
High Density Bipolar 3. An E1 line coding method. This is the more modern line coding method of the two commonly available. See Line Coding, T1. See also AMI and B8ZS
A group of telephone channels configured so that if the first is busy (engaged) the call goes to the next channel, if that channel is busy it goes to the next channel, etc. Hunt groups may hunt from the highest to the lowest, the lowest to the highest, or on some other arbitrary pattern. But the order of hunting will usually be fixed, beginning with one channel and working through ("hunting") until an unused channel is found. The term may have originated back in the old manual switchboard days when the operator literally hunted for an unused jack to plug a cord into. This arrangement is very common in business scenarios where a single incoming number (the Listed Directory Number) is given to the public, but multiple incoming channels are supported. See LDN
A device which converts from a two-wire signal such as POTS lines to a four-wire system (separate send and receive paths) such as used in the pro-audio world. While this task is theoretically quite simple, the fact the impedance of most phone lines varies widely across frequency complicates matters. The Telos 10 telephone system was the first practical DSP (Digital Signal Processing) based hybrid and applied the then brand-new technology to this problem
InterExchange Carrier. "Long Distance" carrier. Handles Interlata and interstate calls. Also referred to as IXC.
Incumbent Local Exchange Carrier. A local Exchange Carrier which entered the marketplace before the enactment of the 1996 Telecom act;. i.e. a telephone company which is neither an Indie nor an RBOC. See LEC and CLEC.
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 tones, however DC loop current signaling also qualifies as In Band Signaling. See also CCIS.
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
A vendor of telecommunications Customer Premise Equipment (CPE) other than a Bell Operating Company (RBOC) 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.
A method of combining and later separating 2 data streams that does not involve the telephone network. Inverse multiplexing is the most common way of achieving this function in Codecs operating at 128kbps or less over ISDN.
IOC Capability Packages
ISDN Ordering Code system. This system was devised by the National ISDN User’s Forum and Bellcore to simplify ordering new ISDN lines in the USA and Canada. Using a single code specifies all line specifications. The Telos Zephyr, ZephyrExpress, TWO, and TWOx12 support IOC package "S". Search for document NIUF 428-94 at NIUF’s web page for more information.
Integrated Services Digital Network- A relatively new and highly flexible type of telephone service which allows dialing on digital lines 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.
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.
A term used in Europe for ISDN BRI. See BRI.
A term used in Europe for ISDN PRI. See PRI.
Incoming Service Grouping. See Hunt Group
IntereXchange Carrier- See IEC.
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 users to understand the status of each line available on a given phone. 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.
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.
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. See also Hunt Group.
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.
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 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. See Channel. See also Station Line
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 and equalizing the circuit.
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 maintained. 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.
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
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.
If your local phone company is an independent then only interstate and inter-phone company calls are considered long distance. 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 IEC, and in some cases RBOCs are being permitted to handle InterLATA calls.
The telephone circuit from the CO to the customer's premises. Generally refers to a copper cable circuit.
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 determines 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 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. 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.
Company which now makes 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 and owns Bell Labs. 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.
Multiple Subscriber Number. This is a telephone number associated with an ETS 300 BRI line. Providers of ETS 300 often give you three MSNs with a BRI, although additional MSNs can be purchased. An ISDN terminal will "ring" (provide an alerting signal) only when calls are made to the MSN (or MSNs) entered in that terminal. If a terminal has no MSNs entered it will "ring" whenever there is a call to any of the MSN’s on that BRI. See ETS 300 and Directory Number.
The first US "standardized" multi-platform ISDN protocol. The first version is National ISDN-1. As of mid 1996 National ISDN-2 has been implemented in some areas and is fully backward compatible with National ISDN-1.
Network Channel Terminating Equipment. NCTE is a general term that can be applied to a CSU or NT1 or other equipment terminating a digital line at the customer’s premises. In many countries the NCTE is provided by the Telco. The USA is not one of those countries.
National ISDN User’s Forum. A user’s group formed under the National Institute of Technology (NIST) in the USA. The NIUF is a neutral forum where the switch manufacturers and Telcos can get input from users and CPE manufacturers regarding the implementation of National ISDN. Among NIUF’s successful projects have been the IOC ordering codes. Their web page is at National Institute of Standards and Technology
. See National ISDN.
Northern Telecom (previously Northern Electric). The Canadian company which was once the manufacturing arm of Bell Canada. Manufacturer of the DMS-100 switch as well as many other pieces of telecom equipment.
"Network Termination Type 1". The termination at the customer premises of an ISDN BRI circuit. The NT1 performs the role of line termination of the "U" interface and Code/Decodes from the line's 2B1Q coding scheme. The customer end of the NT1 interfaces using the "S" or "T" interface. The NT1 is frequently part of the "Terminal Adapter" and is built-in to Zephyr, ZephyrExpress, Telos TWO and TWOx12 systems sold in the USA & Canada.
Private Branch Exchange. A privately owned switch. Basically a PBX is a private "business" telephone system which also interfaces to the telephone network. Many PBX's can now offer ISDN BRI service, usually over the S Interface. A few vendors are now offering BRI over the U interface as well. Be wary of these ISDN protocols since they have not been as well tested. They may or may not work with a given piece of CPE.
Primary Interexchange Carrier. This is your default "1+" carrier used for interLATA calls. In some areas you may have two PICs, one for interLATA calls, and one for intraLATA long distance calls (in which case it stands for Primary Intraexchange Carrier). In some areas intraLATA long distance calls are still handled by your RBOC, in others you now have a choice.
AT&T "Custom Point to Point" Custom ISDN Protocol. Not supported by the Zephyr or ZephyrExpress. See Custom ISDN and ISDN Protocol.
Point Of Presence. The local facility where your IEC maintains a switch. This is where your long distance calls get routed so that your IEC can handle them.
This is a pretty general term. Newton’s Telecom Dictionary 10th edition defines a port as "An entrance to or an exit from a network". Many phone equipment vendors refer to ports as the physical interface between a Switch and a Line or Trunk. Product literature often refers to the number of ports on a phone system. In this context it refers to the number of phone or lines (or sometimes the combination) the system supports.
Plain Old Telephone. A black, rotary-dial desk phone. Usually a Western Electric model 500 set. Outdated term.
Plain Old Telephone Service. Regular old-fashioned analog loop start phone service.
Primary Rate Interface. A form of ISDN with 23 "B Channels" and one "D channel." All 24 channels are on a single cable. Functionally related to T1 telephone circuits. In Europe PRI has 30 "B Channels" and one "D Channel".
The act of configuring an ISDN line. Also refers to the complete line configuration information.
Power provided on pins 7 and 8 of the "S" interface cable. This power is used so that an NT-1 can provide power to a terminal (usually a phone). In some cases it is used to allow a terminal to power an NT1. The U.S. versions of the Zephyr, ZephyrExpress, and Telos TWO supply PS2 power in the "S" jack. This power arrangement is also used in the Telos TWOx12 and 2101 to power Desktop Directors.
AT&T "Custom Point to Point" Custom ISDN Protocol. Point-to-Point lines have only one incoming phone number which must be dialed twice to connect to both lines. See Custom ISDN and ISDN Protocol.
Regional Bell Operating Company. One of the regional companies formed when AT&T got out of the local telephone business. Each RBOC (or "baby bell") owns a number of the former "Bell Operating Companies". The Bell Operating Companies are the traditional local phone companies (pre-1984), except where one’s service is from an "Independent" (non bell) telephone company or a CLEC. Due to their former association with the Bell System RBOCs are regulated by the FCC differently than are independent Telcos. In many cases the Bell Operating Company structure is no longer used. For instance, here in Ohio we now deal directly with the RBOC, Ameritech, while the old Bell Operating Company, Ohio Bell Telephone, no longer exists. Another trend is mergers among the RBOCs (and in some cases the independents as well). See CLEC and LEC.
Receive Data. Data coming from the network, or DCE towards the DTE. Also, a light on a modem or CSU/DSU which lights to indicate presence of this signal.
Regional Bell Operating Company
A device intended to extend ISDN telephone service to site further from the central office than could normally be served. i.e.: beyond 18,000 feet. ISDN repeater technologies include "BRITE", "Virtual ISDN", "Lightspan", and "Totalreach". Some Telcos do not use repeaters. Compatibility between a given piece of CPE and a repeater is less certain than if that CPE were directly connected to the switch.
Robbed Bit Signaling
A signaling scheme that "borrows" bits on each T1 channel for use as signaling channels. On SF T1's there are two bits, the A bit and the B bit in each direction. On ESF T1's there is also a C and D bit in each direction, although they are rarely used. Using these bits, various older analog trunk interfaces can be emulated over a T1. For instance, address signaling using 10 pulse per second (rotary style) digit groups over these bits. Since robbed bit signaling interferes with the least significant bit, only 7 bits can be used for sensitive data applications, leaving only a 56kbps channel for data applications.
See Hunt Group
The electrical interface between the NT-1 and the Terminal Adapter or other ISDN equipment. ISDN equipment with built-in NT1’s do not necessarily provide access to the S interface (the Zephyr, ZephyrExpress and Telos TWO do). Multiple devices can share an NT-1 by connecting on the S interface. Also known as the S passive bus.
European term for ISDN BRI. See BRI and ISDN 2.
European term for ISDN PRI. See PRI and ISDN 30.
Unlike telegraphy, teletypewriter and POTS lines, most digital lines (such as ISDN) use a voltage rather than current mode of operation. Sealing Current allows a controlled amount of current to be passed through a telecom circuit for purposes of "healing" damage caused by corrosion. Bellcore specifies sealing current on the ISDN U interface.
Superframe. A type of Line format supported on T1 circuits. The Telco determines the line format and line encoding of your line. ESF is the preferred Line Format on T1 circuits. See Line Format.
See Statistical Multiplexing