Table of Contents




recEive and transMit (or ear and mouth). Trunking arrangement generally used for two-way switch-to-switch or switch-to-network connections. Cisco's analog E&M interface is an RJ-48 connector that allows connections to PBX trunk lines (tie lines). E&M is also available on E1 and T1 digital interfaces.


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.


1. ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of standard telephone numbers.

2. Name of the field in an ATM address that contains numbers in E.164 format.


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


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 T.120. 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.


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


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.


European Backbone. Pan-European network backbone service.

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.


European Community.

echo channel

See E channel.


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.


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

edge device

1. 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 is not an ATM switch that can connect to an ATM switch.


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


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


end-to-end call manager.


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


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 can 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.


Electronic Frontier Foundation. Foundation established to address social and legal issues arising from the impact on society of the increasingly pervasive use of computers as the means of communication and information distribution.


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 was replaced by BGP. See also BGP.


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.


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.


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 called as RS-232.


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.


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.


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


See EIP (Ethernet Interface Processor) in the "Cisco Systems Terms and Acronyms" section.


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


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.


EtherTalk Link Access Protocol. 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


electronic data interchange

See EDI.

Electronic Data Interchange for Administration, Commerce, and Transport


Electronic Frontier Foundation

See EFF.

Electronic Industries Association

See EIA.

electronic mail

See e-mail.

Electronic Messaging Association

See EMA.

electrostatic discharge

See ESD.


Enhanced Local Management Interface.


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 e-mail, voice mail, and facsimile.


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.


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


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.


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


emulation mode

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


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.


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.


Device that modifies information into the required transmission format.


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.


H.323 terminal or gateway. An endpoint can call and be called. It generates and terminates the information stream.

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


Enterprise System Connection channel

See ESCON channel.


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

entity identifier

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

entity name

Name that an NVE can 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

Part of an entity name that describes the entity's class. For example, LaserWriter or AFPServer. See also entity name.


end of message. Indicator that identifies the last ATM cell containing information from a data packet that was segmented.


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


early packet discard. 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.


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 EECM and PROM.


Technique used to compensate for communications channel distortions.


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 can reduce the ER to a value that the element can sustain. See also ACOM, PCR, and RLM.

erasable programmable read-only memory


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.


1. end system. Generally, an end-user device on a network.

2. end system. Nonrouting host or node in an OSI network.


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


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



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


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.


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


Extended Simple Mail Transfer Protocol. Extended version of the Simple Mail Transfer Protocol (SMTP), which includes additional functionality such as delivery notification and session delivery. ESMTP is described in RFC 1869, SMTP Service Extensions.


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.


Extended Services Processor.


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. A 4ESS is its digital central office for toll center application.


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.

ethernet meltdown

Event that causes saturation, or near saturation, on an Ethernet. It usually results from illegal or misrouted packets and typically lasts only a short time.


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

EtherTalk Link Access Protocol



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


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

European Academic Research Network


European Computer Manufacturers Association


European Telecommunication Standards Institute


European Internet

See EUnet.


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.


European Workshop for Open Systems. The OSI Implementors Workshop for Europe.

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.


See EXEC in the "Cisco Systems Terms and Acronyms" section.


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


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


Extended Industry-Standard Architecture


Extended Services Processor

See ESP in the "Cisco Systems Terms and Acronyms" section.

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.


excessive zeros.

Posted: Tue Sep 21 15:14:25 PDT 1999
Copyright 1989-1999©Cisco Systems Inc.