SNMP4tPC - Network/Computer Glossary of Terms (E to I)

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Glossary of Terms
E to I

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E1 The European standard for high-speed data transmission at 2.048Mbit/s - 32 64Kbit/s channels are provided.

Earth station Transmitting or receiving point for satellite transmission.

EBCDIC (Extended Binary Coded Decimal Interchange Code) An IBM-developed eight-bit binary code that can represent 256 characters. It allows the representation of control codes and graphics in a logical format. It was created to represent data in particular types of data processing and communications terminal devices.

Echo cancellation A technique used in high-speed modems to isolate and remove unwanted signal energy created by echoes of the transmitted signal. (An echo is the return of a transmitted signal). It would be noticeable by its absence on transatlantic or other time-differentiated phone conversations.

ECMA (European Computer Manufacturers Association) An organization dedicated to the co-operative development of standards applicable to computer technology. It works closely with certain ITU-TS Study Groups and ISO Sub-committees.

EDI (Electronic Data Interchange) The interchange of trading information through the use of an electronic messaging system. A form of paperless trading that is rapidly expanding through organizations such as Geis.

EGP (Exterior Gateway Protocol) The protocol used by a gateway in one autonomous system to advertise the IP addresses of networks in that system to a gateway in another autonomous system.

EIA/TIA The US Electronics Industries Association and Telecommunications Industries Association which have merged. The EIA is a US trade organization for the electronics industry that concentrates on hardware interface standards. Best known for the RS232C and RS422 standards that specify the electrical characteristics of interconnections between terminals and computers or between two computers.

EIA/TIA 568 The EIA/TIA's most famous standard specifying a maximum horizontal cable run of 90 meters, allowing 10 meters for hub and device attachment resulting a total cable length of 1000 meters. Its related Service Bulletins TSB 36 and 40 define three categories of cabling system for data communications: Categories 3, 4 & 5.

EISA (Extended Industry Standard Architecture) A 32-bit adaptation of the 8/16-bit buses originally developed by IBM and now standard in almost all PCs that use Intel's 8086 and 80X86 chips. The EISA bus is a joint development from Compaq and other PC manufacturers. Contrast with Microchannel and ISA.

Electronic mail, e-mail The electronic transmission and reception of messages and text-based information without the need for the recipient to be present at the time of the transmission. Available either as a value-added service from providers such as GEIS, IBM and MCI or on LAN systems such as ccMail. De jure standards are evolving, but gateway software in the interim is now sufficiently mature to cope with most interactivity.

EMS (Element Management System) The level of a network management system concerned with collecting network management information from, and setting parameters on the network elements. Network elements consist of data communications and telecommunications equipment.

Emulation Hardware or software, or a combination of the two, that behaves like another device or program, like PCs emulating dumb terminals.

Encapsulation The process of sending data encoded in one protocol format across a network operating a different protocol, where it is not possible or desirable to convert between the two protocols. For example, where Ethernet LANs attach to an FDDI backbone, it is not possible to convert between the different packet formats, so the Ethernet packet is encapsulated in its entirety inside an FDDI packet as it crosses the bridge on to the FDDI network. When the encapsulated Ethernet packet reaches the bridge connecting the destination Ethernet LAN to the FDDI network, the Ethernet packet is stripped out of the FDDI packet and put, unchanged, on to the destination Ethernet LAN. Also known as protocol tunneling.

Entry point An IBM network management term. An entry point provides management functions for itself and the devices attached to it. It has to be an SNA-addressable unit, allowing it to participate in network management by monitoring its own environment and exchanging information and messages with a Focal point.

Error control A means of ensuring that information received across a transmission link is correct. The techniques involved typically use error detection to detect if the transmitted data has been corrupted. The error control technique involves asking for data to be retransmitted until a correct version is received.

Error correction A technique to restore data integrity in received data that has been corrupted during transmission. Error correction techniques involve sending extra data along with the original data being sent. It allows the correct form of the data to be reconstructed from the extra information if the original has been corrupted. This extra information is calculated using particular error correction algorithms such as Hamming Code. It allow errors to be detected and the original data reconstructed. This is sometimes termed forward error correction.

Error detection A set of techniques that can be used to detect errors in received data. Techniques that are applicable include parity checks involving parity bits, checksums or a Cyclic Redundancy Check.

Ethernet The most widely LAN transmission network. Based on a bus network topology, it runs at a maximum 10Mbit/s - in practice far less - and adopts CSMA/CD techniques operating over convention co-axial cable, thin wire co-axial cable and unshielded twisted pair cabling. A fiber-optic implementation has also been defined. Originally developed by Xerox, Intel and Dec, Ethernet has moved through V1 and V2 proprietary definitions, and has now been standardized by the IEEE as the IEEE 802.3 standard. This has several implementations - 10Base5 for use over conventional co-axial cable, 10BaseF for use over optic fiber, and 10BaseT for use over Unshielded Twisted Pair (UTP) cabling.

Ethernet switching A technique inspired by Kalpana bringing the advantages of a parallel networking architecture to current contention- based Ethernet LANs. Each LAN can be segmented, each with its own 10Mbit/s path. When users on different segments exchange data, an Ethernet switch dynamically connects the two separate Ethernet channels without interfering with other network segments. The switch can create multiple independent connections between separate segments, allowing multiple parallel data exchanges. This multiplies network bandwidth without modification to Ethernet end station hardware or software. Once disparaged by other vendors, it now forms part of the portfolio of the major hub and router manufacturers.

Etsi (European Telecommunications Standards Institute) A European standards body established in 1988 by a decision of the CEPT. It has taken over the work of the CEPT the area of developing the Net-Normes Europeene de Telecommunication, Net standards.

Eutelsat Inter-governmental organization founded in 1983 with the launch of Eutelsat 1, Eutelsat aims to provide and operate a space segment for public intra-European international telecommunications services. The segment is also used to meet domestic needs by offering leased capacity, primarily for television. UK and France are the main shareholders, with about 25 members in total.

Ewos (European Workshop for Open Systems) A forum aimed at promoting OSI standards and undertaking the development of functional profiles. Its work includes OSI Layers One to Four, FTAM, MHS, ODA, Directory Services and the VT protocol.
F

Fast Ethernet Proposed 100Mbit/s technology for workstation LANs from the eponymous Fast Ethernet Alliance, which includes 3Com and SynOptics. It has been adopted by the IEEE as the basis for the 100BaseT Ethernet standard.

Fast packet switching A WAN technology capable of transmitting data, digitized voice and digitized image information. It makes use of short, fixed length packets (or cells) that are all the same size. The underlying switching technology is based on the statistical multiplexing of data and voice in fixed length cells. Any of these packets could carry digital voice, data or digital image information. All the packets travel at Level Two of the OSI Model, and routing is performed on the basis of the Level Two addressing. Fast packet is an effective way of making best use of available bandwidth. It offers the benefits of conventional multiplexing techniques and circuit switching techniques. It is one of the transmission technologies being developed for use with B-ISDN. The switch used to route packets in a fast packet network is termed a fast packet switch. Also, fast packet technology can carry data transmissions that enter the network using a frame relay access method. For particularly high speed networking, an implementation of fast packet switching known as ATM is being commercially developed.

Fault tolerance A method of making a computer system or network resilient to faults or breakdowns to avoid lost data and downtime. For servers this involves such techniques as disk mirroring, disk duplexing or mirrored servers. For LANs and WANs it may involve the use of multiple redundant transmission links.

Fax server A specialized IVR system which sends facsimile messages to a fax machine designated by DTMF tones. What amounts to a database of fax text resides in the server that is accessed via a user's DTMF phonepad. Requests result in the fax pages being delivered to the chosen fax and the subscriber charged a fee.

FCC (Federal Communications Commission) US regulatory and approvals agency.

FDDI (Fiber Distributed Data Interface) An optical fiber-based token-passing ring LAN technology with dual counter-rotating rings. Each ring carries data at a rate of 100 Mbit/s using a 125MHz transmission frequency. It has been standardized by the American National Standards Institute (ANSI). An FDDI network has two modes of attachment: a device may be a Single Attach Station - attached to one ring - or a Dual Attach Station - attached to both rings. Typical applications of FDDI are in the area of high speed LAN backbones.

File server A computer, attached to a LAN, that runs a Network Operating System (nos). This lets the file server regulate communications among the workstations connected to it across the LAN, and to manage shared resources available on the file server, such as hard disk storage and printers. A file server may be dedicated: the computer is used only as a file server; or non- dedicated: the underlying computer that the LAN nos runs on is used for another task simultaneously, for example as a workstation.

Flow control The procedures for controlling the rate of transfer of data between two points in a data network, such as between a protocol converter and a printer. This avoids data loss when a recipient device's buffer is full. Buffers play an essential role in overall flow control in a network.

FNC (Federal Networking Council) A US group of representatives from those federal agencies involved in the development and use of federal networking, especially those networks using TCP/IP, and the connected Internet. The FNC coordinates research and engineering. Members include representatives from the DoD, DOE, Darpa, NSF, Nasa and HHS.

Focal point An IBM Network management term; it consolidates the functions needed to manage centrally all parts of a network. It provides an end-to-end network view and receives information from entry points and service points. NetView is IBM's key implementation of the focal point.

Foirl (Fiber Optic Inter-Repeater Link) Defined in IEEE 802.3 and implemented over two fiber links, transmit and receive, this medium may be up to 500m and 1 kilometer long depending on the number of repeaters in the network.

Fractional services Bandwidth available from carriers in increments of 64Kbit/s, such as Mercury's Switchband.

Frame A group of bits sent over a link. A frame may contain control and addressing information, as well as error detection - for example CRC information - and forward error correction information. The size and composition of the frame varies according to the protocol. Often used synonymously with packet.

Frame relay A data communications interface originating from ISDN designed to provide high speed frame or packet transmission with minimum delay and efficient use of bandwidth. It is a variation on the X.25 interface and form of fast packet switching. It derives its name from using the Data Link or "frame" OSI layer Two to route or "relay" a packet directly to its destination instead of terminating the packet at each switching node. This eliminates processing overheads and increases throughput speed. Based on the ITU-TS Lap-D standard, it uses variable-length packets and applicable only to sub-broadband, T3/E3 or lower, data transmission. Like Ethernet, or token ring, frame relay assumes that connections are reliable. It does not have error detection and error control within the network, which helps to speed up the protocol. When errors occur frame relay relies on higher level protocols for error control. Frame relay is often viewed as a replacement for X.25, primarily for LAN-to-LAN bursty traffic. Voice over frame relay is available, but the subject of debate. It will also become an access method for ATM-based WANs.

FDM (Frequency Division Multiplexing) A multiplexing scheme in which the available transmission frequency range is divided into narrower bands. Each of these bands is used to carry a separate channel.

FSK (Frequency Shift Keying) A technique for modulating data that use two frequencies. Frequency shifts between the two frequencies are generated when the binary digital level changes. So one particular frequency is used to represent a binary one, and a second frequency is used to indicate a binary zero. FSK is used in low speed modems when, in full-duplex transmission, two different frequencies are used in each direction, resulting in four different frequencies being used.

Front end The client part of a client/server application that requests services across a network from a server, or back end. It typically provides an interactive interface to the user, for example, a data entry front end, allowing data to be entered into a server through the use of SQL.

FTAM (File Transfer Access and Management) ISO 8671 standard which plays a key role in integrated message handling as the vehicle for interchanges of EDI information between applications. FTAM controls the transfer of whole files or parts of files between end systems.

FTP (File Transfer Protocol) The TCP/IP standard, high-level protocol for transferring files from one machine to another. Usually implemented as applications level programs, FTP uses the Telnet and TCP protocols. Full duplex - A channel capable of transmitting in both directions at the same time.

Functional profile A defined stack of ISO OSI Layer elements, such as Gosip, Map or Top. Functional profiles were developed in order to ensure that, when defined, ISO OSI stacks could interoperate. Due to the different protocol elements at each OSI layer, it was possible to define stacks that were syntactically correct, but would not be able to exchange in-formation due to differences at particular layers. A functional profile that has been defined as a standard is a standardized profile. Likewise, an International Standard Profile is an OSI functional profile.

G recommendations A series of standards defined by the ITU-TS covering transmission facilities. They are: G.703 2.048Mbit/s - transmission facilities running at 2.048Mbit/s that use the ITU-TS recommended physical and electrical interface specified in G.703; G.703 641K - likewise for transmission facilities running at 64Kbits/s; G.703 - the ITU-TS standard 1984 current version for the physical and logical traits of transmissions over digital circuits. G.703 now includes specifications for the US 1.544Mbit/s as well as the European 2.048Mbit/s, and circuits with larger bandwidths on both continents. G.703 is still generally used to refer to the standard for 2.048Mbit/s; G.821 - ITU-TS Recommendation that specifies performance criteria for digital circuits for ISDN.

Gateway Network interconnection device and software that operate at OSI Layer Seven. A gateway supports a full stack of the relevant protocol, such as SNA, DecNet, ISO, TCP/IP, and can covert to a non-seven layer protocol, such as async or BSC. It is typically used to provide access to wide area networks over asynchronous or X.25 links from a LAN environment. Examples include pads and protocol converters.

GFI (Group Format Identifier) (X.25 reference) the first four bits in a packet header, GFl contains the obit, Dbit and modulus value.

GGP (Gateway-to-Gateway Protocol) The protocol that core gateways use to exchange routing information, GGP implements a distributed shortest path routing computation.

Gosip (Government Open Systems Interconnect Profile) Country specific ISO OSI functional profiles that have been defined as part of national procurement policies. The US has US Gosip which is defined as a Federal Information Processing Standard. The UK has the UK Gosip which is defined by the Central Computer and Telecommunications Agency. The UK Government will not buy equipment unless it supports OSI as specified in Gosip. Unfortunately, the various Gosips as published by the UK, US and Japanese governments are all slightly different.

GSM (Global System for Mobile communications) A two-way, pan-European digital cellular system. Its specification is in line with ISDN and ITU-TS System 7 signaling and approved by almost all European countries. GSM operates at 900MHz and is a forerunner to the mass-market Personal Communications Networks, based on the same set of standards. GSM services include current digital subscriber services and the unique Short Message Service - a superior form of paging offering up to 160 alphanumeric characters with guaranteed delivery.

GUI (Graphical User Interface) Often pronounced "goo-ee", it describes the screen display that first greets a user and with which the user interacts during the computer session. A GUI makes use of Windows, Icons, Menus and Pointers - so-called WIMP systems - such as Microsoft Windows, GEM and X-Windows. Apple's GUI is particularly notable and be-spoke GUIs are becoming popular.

Group In the context of network security, a group is a set of users who share common permissions for one or more resources. Individually assigned user permissions take precedence over those assigned through groups.

Guard band The unused bandwidth separating channels to prevent crosstalk.

Guard tone A tone generated by a high speed modem dial-up modem to ensure that there is sufficient bandwidth available on the PSTN circuit for transmission.

H channel The ISDN packet switched channel on Basic Rate Interface, designed to carry user information streams at different speeds, depending on type: H11=1536Kbit/s, H0=384Kbit/s and H12= 1920Kbit/s.

H.261 A ITU-TS standard for video compression know as Codes for Audiovisual Services at N x 384Kbit/s. It sets a common algorithm for converting analog video signals to digital, operating at or above 384Kbit/s.

Half Duplex A two-way means of transmission, but data can only travel in one direction at a time.

Half-bridge Apple Computer terminology for a device linking LANs over a low-speed link such as a telephone line or X.25 link. It is termed a half- bridge as one is required at each end of the link.

Handshake Part of the procedure to set up a datacommunications link. The handshake can be part of the protocol itself or an introductory process: the computers wishing to talk to each other set out the conditions they can operate under. Sometimes, the handshake is just a warning that a communication is imminent.

Head-end A central point or hub in broadband networks that receives signals on one set frequency band and retransmits them or another. Every transmission has to go through the head-end in a broadband network. The head-end is the piece of hardware that enables a network to send and receive on the same piece of cable. In CATV technology, the head-end is the control center for a cable system where signals are processed and sent for distribution down the cable system.

Header The control information added to the beginning of a transmitted message. This may consist of packet or block address, destination, message number and routing instructions.

Hertz A measure of radio frequency. One Hz=one cycle per second. KHz = 1,000Hz; MHz =1,000,000Hz; GHz=1,000,000,000Hz.

HDLC (High level Data Link Control) An ISO standard set of protocols for carrying data over a link with error and flow control. Similar to IBM's SDLC, versions of HDLC are under development for multipoint lines. The ITU-TS later adapted HDLC for its Link Access Protocol used for X.25 networks. It is a bit-oriented data link control procedure under which all data transfer takes place in frames. Each frame ends with a frame check sequence for error detection. There is a control field at the start of each frame that allows error detection, and data link setup and data link termination. HDLC is, in fact, a misnomer, as it is not a high level protocol.

HLMS (Heterogeneous LAN Management Specification) Network management specification developed by IBM and 3Com. It provides an underlying structure for the development of network management products which can function with a variety of network operating systems and adapter cards.

Heterogeneous networking The networking of computers from different vendors, or the running of different operating systems.

Hierarchical network A network with one host at its hub, which is the major processing center, and one or more satellite processing units. IBM's SNA was originally designed as an hierarchical network.

Host processor A minicomputer or mainframe attached to a network providing services to network users.

Hot fixing The ability to detect and mark bad sectors of a disk, then assign alternate disk sectors during routine LAN operation. This automatically updates the original defect map.

Hot swap The ability of a device to have parts removed after, for example, a slot-in card or fan failure, without affecting its operation. Many of today's hubs offer hot swapping without bringing down the network to charge a component.

HPFS (High-Performance File System) An OS/2 file system that has faster input/output than the file allocation table file system; it does not restrict file naming to eight characters with a three character extension; and is compatible with the FAT file system.

HSSI (High speed Synchronous Serial Interface) Interface for transferring data to or from a WAN leased line (E2, E3), or to and from a LAN via an HSSI-capable DSU and HSSI router.

Hub The center of a star topology network or cabling system. A multi-node network topology that has a central multiplexer with many nodes feeding into and through the multiplexer or hub. The other nodes do not usually directly interconnect. LAN hubs are increasingly popular with the growth of structured cabling and the need for LAN management.

Brouter or Hybrid Bridge/Router Network interconnection device with a standard mode of operation as a router. It can support multiple OSI Layer Three routing protocols, but also supports bridging capabilities for network traffic that cannot be routed - non-routable traffic.

I-Series recommendations ITU-TS (formerly the CCITT) recommendations on B-ISDN, ISDN and aspects of ATM.

IAB (Internet Activities Board) The technical body that sets policy and standards for TCP/IP and the connected Internet suite of protocols. Its task forces are the IETF and IRTF.

IBMCS (IBM Cabling System) Cabling system introduced by IBM in 1984 based around Shielded Twisted Pair (STP) cabling.

ICMP (Internet Control Message Protocol) Protocol allowing status messages to be generated by an internetworking gateway, indicating a variety of error or unusual conditions.

ICR (Intelligent Character Recognition) Software similar to OCR, but it learns to recognize different fonts and character styles, so is more efficient. Useful to make paper documents accessible via groupware.

IDA (Integrated Digital Access) The means of providing digital access for subscribers to the BT ISDN service. Two versions: single line IDA and multi-line IDA are available.

IDAPI (Integrated Database Application Programming Interface) A standard from Borland and others providing a standard interface to a wide range of databases. It is supposed to be a superset of ODBC.

IEEE Institute of Electrical and Electronic Engineers: a US publishing and standards organization responsible for many LAN standards such as the 802 series.

IEEE 802.2 The Data Link standard for use with IEEE 802.3, 802.4 and 802.5 standards. It specifies how the basic data connection should be set up over the cable.

IEEE 802.3 The IEEE standardization of Ethernet. A Physical Layer definition that includes specification for physical cabling plus the method of transmitting data and controlling access to the cable. It uses the CSMA/CD access method on a bus topology LAN.

IEEE 802.4 The IEEE standardization of Token Bus. A Physical Layer standard that uses the Token Ring passing access method on a bus topology LAN. Used by LANs implementing the Manufacturing Automation Protocol. The older Arcnet operates in a similar way but does not follow 802.4, but Arcnet supporters have been trying to get the technology ratified by IEEE without success.

IEEE 802.5 The IEEE standardization of IBM Token Ring. A LAN Physical layer standard that uses the Token Ring passing access method on a ring topology LAN.

IEEE 802.6 The standard that defines Mans, an SMDS-based, short packet ATM transmission.

IGP (Interior Gateway Protocol) Term applied to any protocol used to propagate network reachability and routing information within an autonomous system. There is no single standard IGP, but RIP is one of the most common.

IN (Intelligent Network) A sophisticated network capable of recognizing the profile (authorization, chosen services) of its users or subscribers. Carriers offering advanced services will increasingly offer IN services, particularly as the boundary between fixed and mobile networks becomes blurred.

In-band signaling A communications technique in which the part of a signal bearing the data control information is contained within the bandwidth of the signal it is controlling.

Installable file system A file system that can be installed in place of the usual file allocation table file system, such as the high-performance file system.

Intelsat (International Telecommunications Satellite Organization) Founded in 1964 to develop a global satellite communications system, Intelsat has some 120 members, including- BT. The Earlybird (Intelsat 1) satellite was launched in 1965 as the first in a series. Intelsat VII is planned to replace the dozen aging Intelsat V-types which carry two-thirds of the world's telephone calls.

Interface The place or piece of equipment where interaction occurs between two regions or systems or processes. A common example is the RS232-C port or the AUI on LANs between the computer and transceiver.

Internet (1) A group of networks that are interconnected so that they appear to be one continuous network, and can be addressed seamlessly at the Network Layer Three of the OSI model. Typical internets are built using routers, either to form a backbone network comprised of routers, or to link together LANs at the Network Layer.

Internet (2) A collection of networks and gateways, including the Milnet and NSFNET, all using the TCP/IP protocol suite. It functions as a single, cooperative virtual network. The Internet provides universal connectivity and three levels of network services: connectionless packet delivery; full duplex stream delivery and application level services including electronic mail and EDI.

Internet address An IP address assigned in blocks of numbers to user organizations accessing the Internet by the US DoD's Network Information Center. Duplicate addresses can cause major headaches on the network, but the NIC trusts organizations to use individual addresses responsibly. Each address is an eight- bit number (0 to 255). There are three classes: A, B and C, depending on how many computers on the site are likely to be connected. The NIC is running out of Class B addresses, so work is in progress to extend the address format to allow expansion into the next century.

Inter-Process Communications (IPC) Communications between several programs based on one computer or across a number of machines. Alternatively, communication across a network between different processes of the same program between different computers running parts of a single program, or between two programs working together. The most common approaches to IPC in networking circles are probably Application Programming Interfaces such as APPC and NetBios.

IGP (Interior Gateway Protocol) The term applied to any protocol used to propagate network reachability and routing information within an autonomous system. There is no single standard IGP, but RIP is one of the most common.

ICMP (Internet Control Message Protocol) An integral part of the Internet Protocol (IP) that handles error and control messages. ICMP also includes an echo request/reply used to test whether a destination is reachable and responding.

IESG (Internet Engineering Steering Group) A US committee consisting of the IETF chairperson and the six area managers. The IESG coordinates activities among the IETF working groups.

IETF (Internet Engineering Task Force) A US committee concerned with short-term and medium-term problems with TCP/IP and the connected Internet. The IETF is divided into six areas which are further divided into working groups and its chairperson is a member of the TAB.

Interoperability The ability to exchange information between two systems so that the information can be processed meaningfully.

IP (Internet Protocol) The TCP/IP standard protocol that defines the IP datagram as the unit of information passed across an Internet and provides the basis for connectionless packet delivery service. IP includes the ICMP control and error message protocol as an integral part. It provides the functional equivalent of ISO OSI Network Services.

IP address The 32-bit address assigned to hosts that want to participate in a TCP/IP Internet. IP datagram - The basic unit of information passed across a TCP/IP Internet.

IRTF (Internet Research Task Force) A technical group working or problems related to TCP/IP and the connected Internet, The IRTF is divided into a set of research groups. The IRTF chairperson is a member of the IAB.

ISA (Industry Standard Architecture) The 8/16-bit bus architecture originally developed by IBM and now standard in almost all PCs that use Intel's 8086 and 80X86 chips.

ISDN (Integrated Services Digital Network) An approach to switched digital networking that can handle a range of digital voice, data and digital image transmission. It is intended to provide end-to-end, simultaneous handling of digitized voice and data traffic on the same digital links via integrated switches. There are different access channels, according to geographic location. These include Basic Rate Access (2 x 64Kbit/s 161 + 16Kbit/s) and Primary Rate Access (1.544 (US) and 2.048 Mbit/s (Europe). ISDN standards are defined in the ITU-TS's I-Series Recommendations.

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