E.164
The ITU-T’s international public telecommunication numbering plan for the PSTN.

E-carrier
A time-division multiplexed, digital transmission facility, operating at an aggregate data rate of 2.048Mbps and above. E-carrier is a PCM system that uses 64Kbps for a voice channel. E-0 is the basic increment of the PDH hierarchy; it is a single channel with a capacity of 64Kbps. In E-1, 32 channels are multiplexed into one 2.048Mbps E-1 digital channel, also referred to as G.703; 30 channels are used for information, and 2 channels are reserved for signaling and control. Other E-carrier levels are E-2 (8.488Mbps over 128 channels), E-3 (34.368Mbps over 512 channels), E-4 (139.246Mbps over 2,048 channels), and E-5 (565.148Mbps over 8,192 channels).

e-commerce (electronic commerce)
The secure exchange of funds, executed over a network, for goods and services exchanged between parties.

E (extended) link
A link that provides enhanced reliability by providing a set of links from the SSP to a second STP pair.

E&M signaling
A signaling arrangement that uses separate paths for signaling and voice signals. The M lead (derived from “mouth”) transmits ground or battery to the distant end of the circuit, while incoming signals are received as either a grounded or open condition on the E (derived from “ear”) lead.

EBCDIC (Extended Binary-Coded Decimal Interchange Code)
A character set that consists of 8-bit code characters and is widely used for exchanging data between computer systems. It has 256 possible combinations: 17 are used for control purposes; 96 are used for text characters; and the remaining code combinations are unassigned.

eBIP (e-business infrastructure provider)
A provider that saves small businesses time and money with Web-based solutions for human resources, accounting, marketing, group collaboration, and other services.

Ebps (exabits per second)
One billion Gbps.

echo
A wave that has been reflected or otherwise returned with sufficient magnitude and delay for it to be perceived as a wave distinct from that directly transmitted.

echo cancellation
A process that allows full-duplex transmission to occur over a single electrical path. It relies on frequency splitting to derive separate voice and data channels from one wire. This feature is necessary for voice transmission but often interferes with data transmission.

EDFA (erbium-doped fiber amplifier)
An optical amplifier. Erbium is injected into fiber, and as a light pulse passes through the erbium, it is amplified, thus, it does not have to be stopped and processed as an electrical signal. The introduction of EDFAs opened up the opportunity to make use of fiber-optic systems operating at 10Gbps.

edge
The network boundary between the customer and the core or central network.

edge device
A device that can pass packets between a legacy type of network such as an Ethernet network and an ATM network, using data-link layer and network layer information. An edge device does not have responsibility for gathering network routing information, but simply uses the routing information it finds in the network layer using the route distribution protocol.

EDGE (Enhanced Data rates for Global Evolution)
An enhanced version of GPRS that combines digital TDMA and GSM to provide 48Kbps to 69.2Kbps per time slot on an aggregated basis, up to 384Kbps.

edge caching
A system in which Web content is duplicated on a machine close to the end user the first time the user requests the content. Subsequent requests for this content, then, are satisfied from the nearby machine. This improves the speed and reliability of access because it avoids the Internet backbone and its peering points.

EDI (electronic data interchange)
The asynchronous exchange from computer to computer of intercompany business documents (such as purchase orders, bills of lading, and invoices) and information. EDI can be accomplished through OSI standards or through proprietary products.

EGP (Exterior Gateway Protocol)
A routing protocol that is used to exchange network reachability information among organizational networks. EGP indicates whether a network is reachable; it does not weight that decision. EGP has largely been replaced by BGP-4.

EIA (Electronic Industries Association)
A U.S. organization that develops standards in the areas of electrical and electronic products and components.

EIA interface
A standardized set of signals characteristics (time duration, voltage, and current) specified by the Electronic Industries Association.

elastic application
A traditional Internet application that can work without guarantees of timely delivery. Because it can stretch in the face of greater delay, it can still perform adequately, even when the network faces increased congestion and degradation in performance.

ELEC (Ethernet Local Exchange Carrier)
A competitive provider that specializes in providing Ethernet solutions in the local loop and metro area.

electromagnetic spectrum
The electromagnetic waves that can propagate through free space that are created when electrons move. It ranges from extremely low-frequency radio waves of 30 Hz?with a wavelength of nearly the earth’s diameter?to high-frequency cosmic rays of more than 10 million trillion Hz?with wavelengths smaller than the nucleus of an atom. The electromagnetic spectrum is depicted as a logarithmic progression: the scale increases by multiples of 10, so that the higher regions encompass a greater span of frequencies than the lower regions. The greater the span of frequencies, the greater the bandwidth of the media operating over that portion of the electromagnetic spectrum.

electronic tandem networking
Operating of two or more switching systems in parallel.

e-mail (electronic mail)
An application that enables users to send and receive messages and files over their computer networks.

EMI (electromagnetic interference)
The noise on data transmission lines that reduces data integrity. Motors, machines, and other generators of electromagnetic radiation cause it. Shielding can reduce EMI.

emulate
To imitate one system with another, so that the imitating system accepts the same data, executes the same computer programs, and achieves the same result as the imitated system.

encapsulation
The process of encasing one protocol into another protocol’s format. Also called tunneling.

encryption
The process of coding data so that a specific code or key is required to restore the original data. Encryption is typically applied for secure data transmission or to prevent unauthorized reception of broadcast material. Sometimes referred to as scrambling.

end office
The first point of access to the PSTN, or the point at which the subscriber loop terminates. Also referred to as Class 5 office, local exchange, central office, and serving office.

end-to-end optical architecture
A network in which the optical signal never needs to be converted to an electronic signal.

ENUM
A protocol that is the result of work of the IETF’s Telephone Number Mapping working group. The charter of this working group was to define a DNS-based architecture and protocols for mapping a telephone number to a uniform resource identifier (URI) which can be used to contact a resource associated with that number.

enterprise network
A network that connects the computer resources throughout a company and supports a wide variety of the company’s applications.

enterprise wiring hub
A hub that not only connects the PCs on a LAN, it also provides the flexibility to perform a number of network functions that can benefit network administrators and network users in general.

equalization
The introduction of components to an analog circuit by a modem to compensate for signal attenuation and delay distortion. Generally, the higher the transmission rate, the greater the need for equalization.

ERL (echo return loss)
Attenuation of echo currents in one direction caused by telephone circuits operating in the other direction.

error
In data communications, any unwanted change in the original contents of a transmission.

error burst
A concentration of errors within a short period of time as compared with the average incidence of errors. Retransmission is the normal correction procedure in the event of an error burst.

error control
A process of handling errors that includes the detection and correction of errors.

error-correction code
A code that incorporates sufficient additional signal elements to enable the nature of some or all of the errors to be indicated and corrected entirely at receiving end.

error rate
The ratio of the amount of data incorrectly received to the total amount of data transmitted.

ESCON (Enterprise Systems Connection)
A proprietary optical networking system.

ESP (Encapsulated Security Payload)
A security system in which IP datagram data is encrypted.

ESS (electronic switching system)
A system that uses computer-like operations to switch telephone calls.

Ethernet
A baseband LAN specification invented by Xerox Corp. and jointly developed by Xerox, Intel, and DEC. Ethernet networks operate at 10/100/1000Mbps by using CSMA/CD running over thick or thin coaxial, twisted-pair, or fiber-optic cable. Standards are being developed for 10Gbps Ethernet as well. Ethernet is defined in IEEE 802.3.

ETSI (European Telecommunication Standards Institute)
A telecommunications standardization organization.

even parity check (odd parity check)
A test of whether the number of digits in a group of binary digits is even (even parity check) or odd (odd parity check).

exchange
The assembly of equipment in a communications system that controls the connection of incoming and outgoing lines and includes the necessary signaling and supervisory functions. Different exchanges, or switches, can be co-sited to perform different functions, for example, local exchange/central office, tandem exchange, toll/trunk/transit exchange, and so on.

extranet
A network between partnering organizations.

extranet VPN
A VPN that allows an external organization to have defined access into an enterprise’s internal networks and resources.