E

E1

Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 2.048 Mbps. E1 lines can be leased for private use from common carriers. Compare with T1. See also DS-1.

E.164

1. ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of standard telephone numbers.
2. The name of the field in an ATM address that contains numbers in E.164 format.

E2A

Legacy protocols for providing OAM&P functions between a network element and an operations support system. See also OAM&P.

E3

Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 34.368 Mbps. E3 lines can be leased for private use from common carriers. Compare with T3. See also DS-3.

early packet discard

See EPD.

early token release

Technique used in Token Ring networks that allows a station to release a new token onto the ring immediately after transmitting, instead of waiting for the first frame to return. This feature can increase the total bandwidth on the ring. See also Token Ring.

EARN

European Academic Research Network. European network connecting universities and research institutes. EARN merged with RARE to form TERENA. See also RARE and TERENA.

EBCDIC

extended binary coded decimal interchange code. Any of a number of coded character sets developed by IBM consisting of 8-bit coded characters. This character code is used by older IBM systems and telex machines. Compare with ASCII.

E channel

echo channel. 64-kbps ISDN circuit-switching control channel. The E channel was defined in the 1984 ITU-T ISDN specification, but was dropped in the 1988 specification. Compare with B channel, D channel, and H channel.

echo channel

See E channel.

echoplex

Mode in which keyboard characters are echoed on a terminal screen upon return of a signal from the other end of the line indicating that the characters were received correctly.

ECMA

European Computer Manufacturers Association. Group of European computer vendors who have done substantial OSI standardization work.

edge device

1. A physical device that is capable of forwarding packets between legacy interfaces (such as Ethernet and Token Ring) and ATM interfaces based on data-link and network layer information. An edge device does not participate in the running of any network layer routing protocol, but it obtains forwarding descriptions using the route distribution protocol.
2. Any device that isn't an ATM switch that can connect to an ATM switch.

EDI

electronic data interchange. The electronic communication of operational data such as orders and invoices between organizations.

EDIFACT

Electronic Data Interchange for Administration, Commerce, and Transport. Data exchange standard administered by the United Nations to be a multi-industry EDI standard.

EEPROM

electrically erasable programmable read-only memory. EPROM that can be erased using electrical signals applied to specific pins. See also EPROM.

EFCI

Explicit Forward Congestion Indication. In ATM, one of the congestion feedback modes allowed by ABR service. A network element in an impending congestion state or in a congested state may set the EFCI. The destination end-system can implement a protocol that adaptively lowers the cell rate of the connection based on the value of the EFCI. See also ABR.

EGP

Exterior Gateway Protocol. Internet protocol for exchanging routing information between autonomous systems. Documented in RFC 904. Not to be confused with the general term exterior gateway protocol. EGP is an obsolete protocol that has been replaced by BGP. See also BGP.

EIA

Electronic Industries Association. Group that specifies electrical transmission standards. The EIA and TIA have developed numerous well-known communications standards, including EIA/TIA-232 and EIA/TIA-449. See also TIA.

EIA-530

Refers to two electrical implementations of EIA/TIA-449: RS-422 (for balanced transmission) and RS-423 (for unbalanced transmission). See also RS-422, RS-423, and EIA/TIA-449.

EIA/TIA-232

Common physical layer interface standard, developed by EIA and TIA, that supports unbalanced circuits at signal speeds of up to 64 kbps. Closely resembles the V.24 specification. Formerly known as RS-232.

EIA/TIA-449

Popular physical layer interface developed by EIA and TIA. Essentially, a faster (up to 2 Mbps) version of EIA/TIA-232 capable of longer cable runs. Formerly called RS-449. See also EIA-530.

EIA/TIA-586

Standard that describes the characteristics and applications for various grades of UTP cabling. See also Category 1 cabling, Category 2 cabling, Category 3 cabling, Category 4 cabling, Category 5 cabling, and UTC.

EIGRP

See Enhanced IGRP in the Cisco Systems Terms and Acronyms section.

EIP

See EIP in the Cisco Systems Terms and Acronyms section.

EISA

Extended Industry-Standard Architecture. 32-bit bus interface used in PCs, PC-based servers, and some UNIX workstations and servers. See also ISA.

ELAN

emulated LAN. ATM network in which an Ethernet or Token Ring LAN is emulated using a client-server model. ELANs are composed of an LEC, an LES, a BUS, and an LECS. Multiple ELANs can exist simultaneously on a single ATM network. ELANs are defined by the LANE specification. See also BUS, LANE, LEC, LECS, and LES.

ELAP

EtherTalk Link Access Protocol. The link-access protocol used in an EtherTalk network. ELAP is built on top of the standard Ethernet data link layer.

electromagnetic interference

See EMI.

electromagnetic pulse

See EMP.

electrically erasable programmable read-only memory

See EEPROM.

electronic data interchange

See EDI.

Electronic Data Interchange for Administration, Commerce, and Transport

See EDIFACT.

Electronic Industries Association

See EIA.

electronic mail

Widely used network application in which text messages are transmitted electronically between end users over various types of networks using various network protocols. Often called e-mail.

Electronic Messaging Association

See EMA.

electrostatic discharge

See ESD.

EMA

1. Enterprise Management Architecture. Digital Equipment Corporation network management architecture, based on the OSI network management model.
2. Electronic Messaging Association. Forum devoted to standards and policy work, education, and development of electronic messaging systems such as electronic mail, voice mail, and facsimile.

e-mail

See electronic mail.

EMI

electromagnetic interference. Interference by electromagnetic signals that can cause reduced data integrity and increased error rates on transmission channels.

EMIF

ESCON Multiple Image Facility. Mainframe I/O software function that allows one ESCON channel to be shared among multiple logical partitions on the same mainframe. See also ESCON.

EMP

electromagnetic pulse. Caused by lightning and other high-energy phenomena. Capable of coupling enough energy into unshielded conductors to destroy electronic devices. See also Tempest.

emulated LAN

See ELAN.

emulation mode

Function of an NCP that enables it to perform activities equivalent to those performed by a transmission control unit.

EN

end node. APPN end system that implements the PU 2.1, provides end-user services, and supports sessions between local and remote CPs. ENs are not capable of routing traffic and rely on an adjacent NN for APPN services. Compare with NN. See also CP.

encapsulation

The wrapping of data in a particular protocol header. For example, Ethernet data is wrapped in a specific Ethernet header before network transit. Also, when bridging dissimilar networks, the entire frame from one network is simply placed in the header used by the data link layer protocol of the other network. See also tunneling.

encapsulation bridging

Carries Ethernet frames from one router to another across disparate media, such as serial and FDDI lines. Contrast with translational bridging.

encoder

Device that modifies information into the required transmission format.

encryption

The application of a specific algorithm to data so as to alter the appearance of the data making it incomprehensible to those who are not authorized to see the information. See also decryption.

end node

See EN.

end of transmission

See EOT.

end point

Device at which a virtual circuit or virtual path begins or ends.

end system

See ES.

End System-to-Intermediate System

See ES-IS.

Energy Sciences Network

See ESnet.

Enhanced IGRP

See Enhanced IGRP in the Cisco Systems Terms and Acronyms section.

Enhanced Interior Gateway Routing Protocol

See Enhanced IGRP in the Cisco Systems Terms and Acronyms section.

Enhanced Monitoring Services

See Enhanced Monitoring Services in the Cisco Systems Terms and Acronyms section.

Enterprise Management Architecture

See EMA.

enterprise network

Large and diverse network connecting most major points in a company or other organization. Differs from a WAN in that it is privately owned and maintained.

Enterprise System Connection

See ESCON.

Enterprise System Connection channel

See ESCON channel.

entity

Generally, an individual, manageable network device. Sometimes called an alias.

entity identifier

The unique address of an NVE's socket in a node on an AppleTalk network. The specific format of an entity identifier is network-dependent. See also NVE.

entity name

A name that an NVE may assign to itself. Although not all NVEs have names, NVEs can possess several names (or aliases). An entity name is made up of three character strings: object, entity type, and zone. For example: Bldg 2 LaserJet 5:LaserWriter@Bldg 2 Zone. See also NVE.

entity type

The part of an entity name that describes the entity's class; for example, LaserWriter or AFPServer. See also entity name.

EOM

end of message. An indicator that identifies the last ATM cell containing information from a data packet that has been segmented.

EOT

end of transmission. Generally, a character that signifies the end of a logical group of characters or bits.

EPD

early packet discard. A mechanism used by some ATM switches for discarding a complete AAL5 frame when a threshold condition, such as imminent congestion, is met. EPD prevents congestion that would otherwise jeopardize the switch's ability to properly support existing connections with a guaranteed service. Compare with TPD.

EPROM

erasable programmable read-only memory. Nonvolatile memory chips that are programmed after they are manufactured, and, if necessary, can be erased by some means and reprogrammed. Compare with EEPROM and PROM.

equalization

Technique used to compensate for communications channel distortions.

ER

explicit rate. In ATM, an RM cell used to limit the ACR for a transmission to a specific value. Usually the source initially sets the ER initially to a requested rate, such as the PCR. Later, any network element in the path may reduce the ER to a value that the element can sustain. See also ACR, PCR, and RM.

erasable programmable read-only memory

See EPROM.

error control

Technique for detecting and correcting errors in data transmissions.

error-correcting code

Code having sufficient intelligence and incorporating sufficient signaling information to enable the detection and correction of many errors at the receiver.

error-detecting code

Code that can detect transmission errors through analysis of received data based on the adherence of the data to appropriate structural guidelines.

ES

1. end system. Generally, an end-user device on a network.
2. end system. Nonrouting host or node in an OSI network.

ESI

end system identifier. An identifier that distinguishes multiple nodes at the same level when the lower level peer group is partitioned. (Usually an
IEEE 802 address.)

ESCON

Enterprise System Connection. IBM channel architecture that specifies a pair of fiber-optic cables, with either LEDs or lasers as transmitters and a signaling rate of 200 Mbps.

ESCON channel

IBM channel for attaching mainframes to peripherals such as storage devices, backup units, and network interfaces. This channel incorporates fiber channel technology. The ESCON channel replaces the bus and tag channel. Compare with parallel channel. See also bus and tag channel.

ESCON Multiple Image Facility

See EMIF.

ESD

electrostatic discharge. Discharge of stored static electricity that can damage electronic equipment and impair electrical circuitry, resulting in complete or intermittent failures.

ESF

Extended Superframe. Framing type used on T1 circuits that consists of 24 frames of 192 bits each, with the 193rd bit providing timing and other functions. ESF is an enhanced version of SF. See also SF.

ES-IS

End System-to-Intermediate System. OSI protocol that defines how end systems (hosts) announce themselves to intermediate systems (routers). See also IS-IS.

ESnet

Energy Sciences Network. Data communications network managed and funded by the U.S. Department of Energy Office of Energy Research (DOE/OER). Interconnects the DOE to educational institutions and other research facilities.

ESS

Electronic Switching System. AT&T's term for an electronic central office switch. A 5ESS is AT&T's digital central office for end office applications and a 4ESS is its digital central office for toll center application.

Ethernet

Baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. Ethernet networks use CSMA/CD and run over a variety of cable types at 10 Mbps. Ethernet is similar to the IEEE 802.3 series of standards. See also 10Base2, 10Base5, 10BaseF, 10BaseT, 10Broad36, Fast Ethernet, and IEEE 802.3.

Ethernet Interface Processor

See EIP in the Cisco Systems Terms and Acronyms section.

EtherTalk

Apple Computer's data-link product that allows an AppleTalk network to be connected by Ethernet cable.

EtherTalk Link Access Protocol

See ELAP.

ETSI

European Telecommunication Standards Institute. Organization created by the European PTTs and the European Community (EC) to propose telecommunications standards for Europe.

EUnet

European Internet. European commercial Internet service provider. EUnet is designed to provide electronic mail, news, and other Internet services to European markets.

European Academic Research Network

See EARN.

European Computer Manufacturers Association

See ECMA.

European Telecommunication Standards Institute

See ETSI.

European Internet

See EUnet.

event

Network message indicating operational irregularities in physical elements of a network or a response to the occurrence of a significant task, typically the completion of a request for information. See also alarm and trap.

Excess Burst

See Be.

excess rate

In ATM, traffic in excess of the insured rate for a given connection. Specifically, the excess rate equals the maximum rate minus the insured rate. Excess traffic is delivered only if network resources are available and can be discarded during periods of congestion. Compare with insured rate and maximum rate.

exchange identification

See XID.

EXEC

See EXEC in the Cisco Systems Terms and Acronyms section.

expansion

The process of running a compressed data set through an algorithm that restores the data set to its original size. Compare with companding and compression.

expedited delivery

Option set by a specific protocol layer telling other protocol layers (or the same protocol layer in another network device) to handle specific data more rapidly.

explicit route

In SNA, a route from a source subarea to a destination subarea, as specified by a list of subarea nodes and transmission groups that connect the two.

explicit forward congestion indication

See EFCI.

explicit rate

See ER.

explorer frame

Frame sent out by a networked device in a SRB environment to determine the optimal route to another networked device.

explorer packet

Generated by an end station trying to find its way through a SRB network. Gathers a hop-by-hop description of a path through the network by being marked (updated) by each bridge that it traverses, thereby creating a complete topological map. See also all-routes explorer packet, local explorer packet, and spanning explorer packet.

Extended Binary Coded Decimal Interchange Code

See EBCDIC.

Extended Industry-Standard Architecture

See EISA.

Extended Superframe Format

See ESF.

exterior gateway protocol

Any internetwork protocol used to exchange routing information between autonomous systems. Not to be confused with Exterior Gateway Protocol (EGP), which is a particular instance of an exterior gateway protocol.

Exterior Gateway Protocol

See EGP.

exterior router

Router connected to an AURP tunnel, responsible for the encapsulation and deencapsulation of AppleTalk packets in a foreign protocol header (for example, IP). See also AURP and AURP tunnel.