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
E1 - European version of T1. Available to users in countries operating under the guidance of the International telecommunications Union (ITU). E1 has a total of 32 channels - 30 for voice and 2 for framing and signaling at a digital bit stream of 2.048 Mbps - compared to the 24 voice channels and 1.544 Mbps of a standard T1.
E3 - European version of T3, with smaller bandwidth and fewer subchannels than a T3. Found in all countries other than the United States, Singapore, and Japan.
Electronic Data Interchange (EDI) - Series of standards which allow different companies and computers to exchange business documents over phone lines, computer-to-computer.
Electronic Serial Number (ESN) - Unique number assigned to all cellular telephones. Programmed into the phone and used by the cellular carrier for authorization and validation purposes. Generally, cellular customers are unaware of their specific ESN.
Electronics Switching System (ESS) - Programmable, software-driven computing used to control the switching of calls, billing information and handling other related network functions. Replaced earlier generation of electromechanical switching equipment which was hardware-based.
Emulation - Where a PC is set up with terminal emulation software to act or communicate as a dumb I/O terminal, allowing the PC to "look" like the terminal it is emulating.
Encapsulation - Where additional routing/signal bits are added to the beginning and/or end of a binary data stream. As the data moves down level (toward the physical layer of a network0, it receives additional headers, and as it moves up level (toward the host application) - headers are stripped off.
Encryption - Translation of data into a secret code to achieve data security. Encrypted data is known as cipher text, non encrypted data is known as plain text. To read an encrypted file - you need a key or password to decrypt it.
End Office (EO) - Switching center where subscriber lines are terminated and where toll calls are switched through to the terminating destination.
End user - The customer.
Enhanced Interior Gateway Routing Protocol (Enhanced IGRP) - Used by routers; a distance/vector based traffic control program.
Error Rate - Transmission test equipment, software, or network adapters may have a separate ability to transmit a known group of packets over a network in order to measure how accurately they are returned - the percentage of packages with errors is known as the error rate.
Ethernet - LAN protocol, which can be connected in either a bus or star topology, allowing personal computers to communicate with each other. A star topology is where all the computers individually connect to a single hub, a bus topology is where all the computers connect to each other through the same wire, without a hub.
Excess Information rate (EIR) - On a frame relay data link connection; data transfer in bits per second that exceeds the Committed Information rate (CIR). Frame relay service providers usually try to transport customer data at a rate equal to the EIR, but only guarantee to transport it at the CIR 95% to 99% of the time.
Exchange (EX) - (1) Telephone switching center; an aggregate of traffic-carrying devices, switching stages, controlling and signaling means at a network node that enables subscriber lines and/or other telecommunication circuits to be interconnected as required by individual callers. (2) Room or building with manual or automatic switching equipment, allowing terminating telephone lines to be interconnected. (3) Territory served by a network numbering exchange (NXX) where local service rates apply.
Exchange Area - With its own legal regulations on how companies can compete/price/package service, an Exchange Area is served by multiple communication companies and central offices.
Extended Superframe Format (ESF) - A type of T1 line - with 12 - 193 bit frames. The additional bit over a 192 bit frame is a 'timing' bit. A superframe is 12 of these 193 bit frames, and the 12 timing bits in each of the 193 bit sequences to mean something else, rather than just timing - such as signaling, dial tone, digits dialed, off hook, or busy. Within the 24 channels - if the least significant bit of the 6th and 12th samples of each frame are used for additional maintenance, control, and signaling, this is called "bit robbing", which is why in-band signaled T1 lines have 56 kbps of bandwidth. Non-bit robbed (aka clear channel) T1 lines have 64 kbps of bandwidth.
Extension - On a PBX or key system, a telephone or equipment connection.
Facilities - Either refers to equipment needed to complete a communications objective (such as twisted copper pairs, coax, or fiber optic), or the part of an X.25 packet header that defines and negotiates window & packet size, transfer speed, and protocol.
Facilities Based Carrier - Unlike a reseller, this would be a telephone company that has its own communication facilities and switches.
Fax On Demand - On voice-response systems, a feature that allows a caller to listen to a recorded message, and then select which information they want to have automatically faxed to.
Feature Code - A code that activates a PBX or public telephone network feature. Example - dialing *69 to dial back a person that called you last.
Feature Group - On a PBX system, where features are assigned to a group to minimize programming of individual phones. Example - assigning transfer to button 1, speed dial on buttons 5,6,7,8,9, do not disturb on button 2, voicemail on button 3…etc - then, assign extensions to this group so that each extension assigned to this group will have these features.
Fiber Distributed Data Interface (FDDI) - LAN backbone protocol, requiring its own NIC cards / software/ fiber optic cabling for configuration. Maximum throughput of a FDDI is 100 Mbps; and twice as expensive as Ethernet or Token Ring architecture. Maximum ring sie is 62 miles, with repeaters every 1.25 miles.
Fiber Optic - Thin strand of very small layers of glass with different refractive properties that channel light through it by bending the rays of light. As the light travels through the core of the fiber, it is bent back toward the core when it enters the cladding.
Fiber Optic Distribution Panel - Aka fiber optic distribution bay - a termination device and organizer.
File Transfer Protocol (FTP) - Internet Protocol (IP) application for transferring files between network nodes.
Foreign Exchange (FX) - Circuit that connects a subscriber in one exchange with a central office in another exchange.
Foreign Exchange Service - A service where a customer line(s) are fed from a different central office than the one that actually serves the customer. Becoming obsolete due to number portability.
Forward Error Correction (FEC) - Where lost data is recouped via a code that is used to attempt repair or correction of damaged data, saving bandwidth by avoiding retransmission. Another method of error correction is Backward Error Correction, where the receiver requests retransmission of the data.
Forward Explicit Congestion Notification (FECN) - Where a bit in the overhead of a data packet in a frame relay network is set 1 if the packet travels through network congestion in the same direction it is flowing, that signals the network to higher level protocols to take flow control action. Example - Done to keep the data packet flow from exceeding the CIR for the connection, and a counterpart to BECN.
Fractional T1 (FT1) - Use of bandwidth in 56/64 kbps (DS0) increments of a T1 facility or up to 24 channels at 1.544 Mbps.
Fractional T3 (FT3) - A private line service where 4,8,12,or 16 T1 circuits are combined together.
Frame - Data unit at the data link / physical layers of the Open Systems Interconnect model, transporting payload data through its layers. Consists of two sections, a header and the data, or the overhead and the payload. Headers carry addresses and routing control info, the data section carries the actual data. ATM, Frame relay, X.25, and T1 all have different framing formats. One complete sampling and conversion cycle of a multiplexed data transmission.
Frame Relay - Form of packet switching based on the LAPD protocol that employs statistical multiplexing over a shared network, intended for use between intelligent end-points and implemented over high-quality transmission facilities that connect programmable switches. The end-points are responsible for end-to-end integrity.
Frequency Division Multiplexing (FDM) - Where two or more signals are "multiplexed" (i.e. encoded into one channel) over radio waves via the combination of multiple frequencies.
Full Duplex (FDX) - Where a communications line or path can communicate in both directions (i.e. both transmit and receive) at the same time.
Gateway - Conceptional or logical network station that interconnects two otherwise incompatible networks, network nodes, subnetworks or devices; performs protocol conversion operations across a wide spectrum of communications functions or layers. The former name for a router.
Gigahertz (GHz) - Giga = billion. 25 GHz means 25 billion Hz, or 25,000,000,000 Hz.
Gigabit - One billion bits
Gigabyte - One billion bytes.
Global Area Network (GAN) - Network classification. LAN is Local Area Network, MAN is Metropolitan Area Network, WAN is wide Area Network.
Ground Start Trunk - Phone line that uses a ground, rather than a short, to signal the central office for a dial tone.
Group - In frequency division multiplexing, number of voice channels, either alone or within a supergroup; normally composed of up to 12 channels occupying the frequency band 60 kHz to 108 kHz.