Index - A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z
EARTH STATION (GROUND STATION) - A microwave radio transmitting and receiving station working with communications satellites. This term most closely associated with large common carrier operations, particularly international.
EARTH TERMINAL - Microwave radio equipment used to communicate with communications satellites. This term most commonly associated with VSATs, TVROs, portable and mobile satellite operations, particularly domestic.
ECHO - A signal that has been reflected or otherwise returned with sufficient magnitude and delay to be perceived at the far end of the circuit. Both " talker echo " and " listener echo " are defined terms. " Echo suppressors ," now largely being replaced by " echo cancelers ," are designed into circuits requiring treatment for echoes.
ECHO CANCELER - A echo removal device that operates by generating an exact opposite of any echo signal and injecting it into the transmission path to cancel echoes. Used in both speech telephony and in some higher-speed dial-up data modems, notably those compliant with CCITT V.32.
ECHO CHECK - One method of verifying accuracy of data transmission; functions by returning (echoing) received data back to the transmitter as verification; primarily used on async data links.
ECHOPLEX - An echo checking data accuracy method used rather commonly and specifically for async keyboard terminals; the received data at the computer port is echoed back to be used as the terminal operator's CRT screen copy; the operator is the error checker.
ECHO RETURN LOSS (ERL) - The loss in the echo path; as a specification, the amount of loss required in the return path to reduce echo to a tolerable level.
ECHO SUPPRESSOR - A speech-activated switch that detects echo conditions and cuts off the echo path momentarily when echo conditions exist; largely obsoleted by echo cancelers.
EDIT - Preparation of data for a later operation; may include rearrangement or addition of data, deletion of unwanted data, format changes, code conversion, or data compression.
EIA RS-232 - The most common DTE serial interface by far, in use for almost 30 years, with several revisions and additions; international equivalent: The suite of CCITT V.24 and V.28 combined with ISO 2110.
EITHER END HOP OFF (EEHO) - In private networks, a switch program that allows a call destined for an off-net location to be placed into the public network at either the closest switch to the origination or to the destination. The choice is usually by time of day. Capable of either Head End Hop Off ( HEHO ) or Tail End Hop Off ( TEHO ) as required.
ELECTROMAGNETIC SPECTRUM - The entire range of wavelengths ( the inverse of frequency ) of electromagnetic waves extending from cosmic and Gamma rays down through visible light and heat to every form of radio communications signal.
ELECTRONIC KEY TELEPHONE SETS (EKTS) - A generic term indicating key telephones with built-in microprocessors which allow access to PBX-like features as well as access to multiple CO lines, using 2 to 4 pair wiring.
ELECTRONIC MAIL - 1.) A common-carrier data communications service to transmit computer-generated messages between locations or cities; 2.) A feature of LANs for transmission of computer-generated messages within a closed community of users on the LAN. Note that the two forms of electronic mail may be used independently or they may be interfaced.
ELECTRONIC SWITCH - A programmable switching system (often denoted ESS, for Electronic Switching System) used in most LEC telephone companies, by all long distance companies, and most end users of PBXs. Completely solid state electronics, as opposed to older electro-mechanical switches.
ELECTRONIC SWITCHING SYSTEM (ESS) - A Bell term for electronic telephone exchange switching equipment; the largest PBXs of thousands of station lines may be Bell ESS machines modified for use as a PBX.
ELECTRONIC TANDEM NETWORK (ETN) - 1.) A private network automatically and electronically connecting the calling office to the called office through Tandem-Tie Trunks. The network switches also function as PBXs; 2.) An AT&T product name; 3.) Used as a generic term for a PBX-based private network by some parties.
EMULATE/EMULATION - Imitating a system or device such that a connected device accepts the same information, executes the same computer programs and achieves the same results as if the emulator were one of its own kind. Most often, emulation is a downward step in capability of the device being used, as when a personal computer is used to emulate a mechanical teleprinter or a "dumb" terminal on a computer network. While some degree of upward emulation is possible, it is less prevalent in the broad view of computer communications.
ENCRYPTION - The systematic encoding of a message or bit stream before transmission to prevent unauthorized recipients from understanding it. The process of again rendering the information readable is DECRYPTION. ENHANCED PRIVATE SWITCHED COMMUNICATIONS SERVICE (EPSCS) - A private network utilizing Bell provided equipment located in the central office and dedicated to a specific customer. In one sense, EPSCS is electronic Centrexes combined with tielines.
E&M LEADS (E & M LEADS, E and M LEADS) - A pair of signaling leads for telephone trunklines carrying signals between trunk equipment or to separate local loop signaling equipment units. The M lead transmits battery or ground signals toward the line signaling equipment, and the E lead receives open or ground signals from the line signaling equipment.
E&M SIGNALING (E & M SIGNALING, E and M SIGNALING) - An arrangement for supervisory (and sometimes dial pulse) signaling between a line circuit and an associated signaling unit effected over two leads providing full- time, 2-way, supervision. Originally used widely only within toll offices for 75 feet maximum, several variations now permit use over much longer distances.
ENTERPRISE NUMBER - An telephone numbering service on which the LEC will supply its operator services to accept charges for all inbound calls without an acceptance check from the customer. Numbers often take the form of "ENterprise NNNN," or the operator term, "WX NNNN," where NNNN is the assigned number for the account. Largely automated today by the "976" offerings of LECs.
EQUAL ACCESS - Provision by Local Exchange Carrier (LEC) switches of ability for other long distance companies than AT&T to be the "1+" primary long distance company for users of long distance (by providing a new type of " Feature Group D " access connection arrangement, FGD ). Also provides " 10-XXX " dialing for secondary and casual calling; generates true hardware Answer Supervision when calls are terminated over FGD circuits, and provides ANI (Automatic Number Identification) on originating calls, so calls can be billed automatically on any IEC the user selects. Some 350 IECs have obtained Bellcore-issued Equal Access code numbers; for example, dialing 10222 nationwide will route a call via MCI, no matter what IEC the line has been presubscribed to.
EQUALIZATION - The procedure of compensating for fluctuation in circuit amplitude, or envelope delay distortion.
ERGONOMICS - a discipline treating the consideration of human factors in design of the working environment and its components; intended to promote productivity and safety in the tools people work with.
ERLANG - A widely-used unit of telecommunications traffic intensity, named after work of the Danish statistician, D. K. Erlang. One Erlang is the intensity at which one traffic path would be continuously occupied, e.g. one call per hour; equivalent to 3600 call-seconds or 36 ccs in early Bell traffic engineering systems.
ERLANG B TABLE - A widely used table derived from D.K. Erlang's statistical work; provides determination of the traffic capacity of a given group of circuits, or inversely permits estimation of the number of circuits needed for a given user group. Later work has resulted in so-called " Erlang C tables ."
ERROR - 1.) In data communications, any unwanted change in the contents of a transmission; 2.) In data processing, incorrect performance of a program routine, data entry, or unwanted stoppage by software or hardware flaws in the computer.
ERROR BURST - The result of an event that causes a stream of consecutively transmitted bits to be corrupted. Engineering studies of more than 5 decades consistently show data transmission errors to have a "bursty" character; this has been widely documented.
ERROR CONTROL - In data communications, methods used to detect and correct transmission channel errors.
ERROR RATE - 1.) In data communications, the ratio of bits, characters, elements, blocks, messages or files incorrectly received to the total number transmitted during a specified time interval; 2.) In business operations or factory production, a similar measure on human performance of transactions or tasks.
ETHERNET - Originally the trade name for a LAN developed by Xerox Corporation; later supported by Digital Equipment Corporation, Intel Corporation and Hewlett- Packard; now standardized as IEEE specification 802.3 .
EXCHANGE - A local telephone switching center or " Central Office "; in some LEC parlances, the group of local switching centers for a community. EXCHANGE NETWORK FACILITIES FOR INTERSTATE ACCESS (ENFIA) - LEC pricing arrangements for local loops offered to IECs for connecting IEC interstate and interLATA networks to LEC central offices.
EXCLUSION - A line privacy arrangement in telephone station equipment to keep other extensions or pick ups off the line when the primary phone is off hook. Some arrangements are automatic, others manual; use has expanded to provide avoidance of interruption to dial-up data positions.
EXTENDED AREA SERVICE (EAS) - Adding expanded local calling areas to a caller's basic local calling area for a (generally) small additional monthly fee. The EAS local calls can be either free (after a small additional monthly fee is paid) or at a cost of reduced per call charges. EXTENDED BINARY CODED DECIMAL INTERCHANGE CODE (EBCDIC) - IBM's proprietary 8-bit code for synchronous data communications. Has numerous variations of control character meanings; is undergoing some standardization as IBM moves SNA and SAA forward.