SNMP4tPC - Network/Computer Glossary of Terms (A to D)

Auto partition A feature of 10 BaseT. When 32 consecutive collisions are sensed by a port in a hub or concentrator from its attached work station or network segment, or when a packet that far exceeds the maximum allowable length is received, the port stops forwarding packets. The port continues to monitor traffic and will automatically begin normal packet forwarding when the first correct packet is received.
B

BABT (British Approvals Board for Telecommunications) An independent organization that tests telecommunications equipment. Its processes are known for their rigorousness and labyrinthine complexity.

Back end The server part of a client/server application. It provides services across the network that have been requested by the client. For example, a back end may be a database server that responds to SQL requests from a workstation running a front end application.

Back-up server Software or hardware which copies files so that there are always two current copies of each file. Also known as a shadow server.

Backbone A high-capacity network that links together other networks of lower capacity. A local backbone network would typical y be an FDDI network acting as an in building backbone to link together multiple LANs. A wide area backbone network would typically use digital leased circuits and multiplexers or routers.

Background Task or Mode A secondary function perforated by a computer without interrupting its current or primary task.

Back-up domain controller A server in a network domain that keeps and uses a copy of the domain's user accounts database to validate logon requests.

Balun A transformer that levels out impedance differences so that a signal generated on to a coaxial cable can transfer on to twisted pa r. Baluns are often used so that IBM 3270 terminals can run off twisted pair, or to allow co-axial Ethernet to be operated over UTP.

Bandwidth The range of frequencies a transmission line or channel can carry: the greater the bandwidth, the greater the information - carrying capacity of a channel. For a digital channel this is defined in bit/s. For an analog channel it is dependent on the type and method of modulation used to encode the data.

10Base2 A form of Ethernet and IEEE 802.3 network cabling using thin coaxial. It refers to I0Mbit/s speed Baseband transmission over 200 meters maximum length in practice 185m) and is commonly known as Cheapernet.

10Base5 A form of Ethernet and IEEE 802.3 network cabling using thick coax. It refers to 10Mbit/s speed Baseband transmission and 500m maximum length.

10BaseT A form of Ethernet and I EEE 802.3 network cabling using twisted pair cabling. It refers to 10Mbit/s speed Baseband transmission twisted pair cable with a maximum segment length of 100m.

100BaseT IEEE standard from proposals by the Fast Ethernet Alliance (including 3Com and SynOptics). It will support Category 3,4 & 5 UTP cabling.

100BaseVG-AnyLan A competing proposal to 100BaseT (promoted by Hewlett Packard, IBM and Proteon among others) to the IEEE for a 100Mbit/s standard over voice grade UTP the cable most users already have installed in existing 10BaseT systems. Based on Quartet Signaling and demand priority protocol, it preserves the infrastructure and will need only a new hub and upgraded adapters in PCs/work stations. It claims support for Category 3,4 & 5 UTP cabling for both Ethernet and Token Ring.

Baseband A term defining any network in which the information is modulated onto a single carrier frequency. The digital input is applied directly to the transmission media without the intervention of a modulating device, which works well if there is wide bandwidth and distances no more than several hundred meters are involved. It is common in LANs and limited distance modems. All stations attached to the network have to participate in every transmission. Simpler and cheaper than Broadband, it permits only one "conversation" at a time as the whole of the bandwidth is used to transmit a single digital signal. Ethernet is a baseband network.

Base station A fixed radio transmitter/receiver which electronically relays signals to and from mobile voice and data terminals or handsets.

Basic Rate Access Two 64 Kbit/s "B" channels + one 16 Kbit/s "D" channel (2B + D), carrying user traffic and signaling information respectively to the user via twisted pair local loop.

Baud A unit of s gnarling speed, expressed in terms of the number of discrete conditions or signal events per second. It is on y the same as bit/s, when one discrete signaling condition is used to transmit a single bit of data.

Beaconing Token Ring process to recover the network when any attached station has sensed that the ring is inoperable because of a hard error Stations can withdraw from the ring if needed. A station detecting a ring failure upstream transmits (beacons) a special MAC frame used to isolate the location of the error using beacon transmit and beacon repeat modes.

Bindery A database that contains definitions for entities such as users, groups and workgroups in the Novel NetWare LAN network operating system environment. The bindery supports the design, organization and secure operation of the NetWare environment.

Bipolar transmission Method of sending binary data in which negative and positive states alternate. Used in digital transmission facilities.

B-ISDN (Broadband ISDN) The proposed advanced version of ISDN, providing speeds of 155.52Mbit/s and higher. Standards and switching technology that will work this fast are under development. It promises universal coverage based on ATM/SDH technologies and optical fiber, supporting data, voice and video traffic.

Bit A binary unit of information that can have two values, 0 or, 1. The word comes from a contraction of binary digit.

Bit Error Rate The percentage of received bits on a digital link that are in error relative to the number of bits received, usually expressed to a power of I 0

Bit Error Rate Tester A device for testing the reliability of a digital datacommunications link. The BERT generates specific data patterns that are routed through a communications device for comparison at the receiving end. The errors are counted by the BERT.

Bit Interleaving A form of Time Division Multiplexing (TDM) for synchronous protocols, including HDLC, SDLC, BiSync and X.25 Bit inter-leaving retains the sequence and number of bits, so that correct synchronization is achieved between both ends.

Bits per second The rate at which individual bits are transmitted across a communications link or circuit; written bit/s. One thousand bit/s is 1 Kbit/s, and one mil ion bit/s is 1 Mbit/s.

Block A group of characters or bytes treated as a unit.

BNC connector A cylindrical push-and-twist connector for connecting thin co-axial cable, such as 10Base2 "thin wire" Ethernet, and to link thin wire Ethernet to network interface cards, transceivers and other network elements. Said to be short for Bayonet Neill-Concelman after the developers of the connector. Also referred to as a Barrel Nut Connector.

Booting Loading a computer memory with information needed for it to operate. Remote booting refers to loading software over the network.

Boundary Routing A 3Com proprietary name for a method of accessing remote networked locations, such as a bank branch office. Effectively a form of bridging, the idea is to reduce the need for technical expertise locally and the cost of equipment at the remote site and manage the communications from head office.

BRA (Basic Rate Access) BRA provides ISDN users with access to two 64Kbit/s data channels, It is defined in ITU-TS Recommendation I.420 which covers a 2B + D-channel where the B channel is a 64Kbit/s channel, and the D-channel is a 16Kbit/s signaling channel.

Bridge Device connecting two separate networks at the OSI Data Link Layer (Level Two Media Access Control Layer). Once bridging is accomplished, the bridge makes interconnected LANs look like a single LAN, passing data between the networks and filtering local traffic. There are two key classifications of bridge: those supporting Spanning Tree and, for Token Ring networks, those supporting Source Routing. Bridges connect networks using dissimilar protocols and do not interpret the data they carry. They control network traffic and security, filtering where necessary to boost network, performance and contain sensitive data to particular LAN areas.

BS5750 A British Standards Institute standard with certification procedures that says an organization is in control of its quality procedures, at least in terms of consistency. Now identical to IS09000.

BSC, BiSync (Binary Synchronous Communications) Rules developed by IBM for the synchronous transmission of binary coded data as a serial stream of binary digits. Synchronization is achieved by using control characters recognizable as bit patterns which do not appear within the body of the message.

BSGL (Branch Systems General License) A license which must be obtained by any organization seeking to link its own private network to the Public Switched Telephone Network (PSTN). A separate license must be held for each individual site.

BSI (British Standards Institute) The UK standards body responsible for input into European and international standards setting bodies like ISO and the ITU-TS.

Broadband Also referred to as wideband. A term describing any network that multiplexes multiple, independent network carrier frequencies on to a single cable. It allows multiple simultaneous "conversations", since the independent networks operate on different frequencies and do not interfere with each other. In LAN terminology, it refers to a system in which multiple channels access a medium, for example co-axial cable, that has a large bandwidth using Radio Frequency (RF) modems. This may allow the co-axial cable to carry multiple separate LANs whose transmission is being modulated at different frequencies. In cable television (CATV), broadband describes the ability to carry 30 or more TV channels and is synonymous with wideband.

Broadcast The simultaneous transmission of data via a network from one terminal to a set of destinations or to all destinations.

Brouter An industry term for a device with the functionality of a bridge and router. It supports more than two LAN connections and uses Level Two addresses for routing. The term is mostly used by bridge vendors.

Buffer A temporary storage place for data, designed to compensate for a difference In transmission speeds or to hold data when there is a difference in timing of events. It can be a software program, a storage facility or a hardware device, ensuring the data always has somewhere to go, even if it has to be held up for while in the buffer until it can be transmitted to the destination.

Bus topology A type of network in which all tie devices are connected in a line to a single cable. A bus network has two distinct ends. All devices which attached to a bus network have equal access to it and they can see all the messages that are put on to the network. Each device determines which messages are intended for it alone, and selects those.

Byte Eight bits forming a unit of data. Usually each byte stores one character.
C

CAI (Common Air Interface) The CT2 international mobile communications standard which allows any compliant equipment to be used on any network of the same type. CAI compliant telepoint handsets from different vendors may therefore be used on a telepoint network. Vendors with CAI compliant systems include Northern Telecom and GPT.

CATV (Cable TeleVision) Cable system covering defined areas, such as the U K's franchises to install and operate a cable system granted by the Cable Authority and Department of Trade & Industry, offering TV channel output and, increasingly, local loop digital telephony services The Cable Television Association is the CATV industry's representative organization.

Call processing The system and process that sets up the intended connection in a switching system. A system scans the trunk and station ports for any requests for service. It then checks the stored instructions and look-up tables and sets the connection up accordingly.

Carrier signal The underlying frequency or frequencies that are to carry information. They are modulated through one or more modulation techniques to impose information on the signal.

Category 3 cable Standard for UTP voice grade cabling specified by the EIA/TIA 568 standard for use at speeds up to I0Mbit/s including 10BaseT Ethernet.

Category 4 Cabling standard specified by EIA/TIA 568 for use at speeds up to 20Mbit/s including 16Mbit/s Token Ring.

Category 5 Cabling standard specified by ElA/TIA 568 for use t speeds up to 100Mbit/s including FDDI (TP PMD), 100BaseT and 100BaseVG-AnyLan, and potentially ATM at 155Mbit/s.

CCITT (The International Telegraph and Telephone Consultative Committee) Former name for the ITU-TS (International Telecommunications Union), a Specialized Agency of the United Nations.

CCITT Study Groups The ITU-TS (formerly the CCITT) operates as a series of groups considering specialist areas. There are key study groups applicable to networking and communications such as Study Group VII responsible for data communications networks and the X series Recommendations and Study Group XVIII covering digital networks including ISDN.

CCTA Central Computer & Telecommunications Agency - the Government Center for Information Systems.

Cell Relay Generic term for a protocol based on small fixed packet sizes capable of supporting voice, video and data at very high speeds. Information is handled in fixed length cells of 53 octets.

Centronics interface A parallel interface with 36 pins that will transmit eight data bits simultaneously. The interface originates from the Centronics Company, a printer manufacturer. It has become widely used as a parallel interface standard.

CEPT The European Conference of Postal and Telecommunications Administrations. An association of European Telecommunications service providers. It in turn participates in relevant areas of the work of Cen/Cenelec. Formerly extremely powerful and was originally responsible for the Net standards, but these have subsequently been passed on to Etsi.

Character Interleaving A form of TDM used for asynchronous protocols. This can be used either with extra channels, or by carrying RS232-C control signals.

Cheapernet Thin wire Ethernet.

Circuit switching The transmission technique in which a physical circuit is established between sender and receiver before transmission takes place. When the transmission is complete, the circuit is freed.

CLI (Calling Line Identification) A service available on digital phone networks that tells the person being called which number is calling them. The central office equipment identifies the phone number of the caller, enabling information about the caller to be sent along with the call itself. Synonymous with ANI (Automatic Number Identification).

Client/server computing The division of an application into two parts; a front end client and a back end server. It allows multiple front ends running on a PC or Unix workstation (client) to access the same SQL based server database at the same time over the LAN. The aim is to off-load as much processing as possible to the intelligent desktop leaving only the shared information and the software for managing it at the central server. An application that is running in such a fashion with client and server linked by a LAN is termed a bifurcated application.

Cluster controller An IBM device that allows multiple 3270 terminals to be linked directly to a host computer, or into a SNA network through the use of a communications controller. A cluster controller is a Control Unit in IBM speak.

CMIP/CMIS (Common Management Information Protocol/Common Management Information Services) ISO OSI connection oriented network management protocol and set of services. Well accepted in the WAN and telecommunications world, they have not yet been widely adopted for LAN management.

CMOT (CMIP/CMIS over TCP) The use of SO CMIP/CMIS network management protocols to manage gateways in a TCP/IP Internet. CMOT is a co-recommended standard with SNMP.

Co-axial cable A cable comprising a central wire surrounded by a second tubular screening of fine wire. Associated with IBM for linking terminals and other devices needing high-speed links, coax is used in Ethernet. It is difficult to add or remove devices from a coaxial LAN as the cable is unwieldy and thick so is being superseded by UTP.

Collision The result of two devices on a shared transmission medium, like Ethernet, transmitting simultaneously. Data is corrupted and both devices must retry their transmissions. A delay mechanism used by both senders drastically reduces the chances of another collision.

Collision detection Devices at each end of a link are designed to detect collisions instantly and attempt to resend. This is the principle on which CSMA/CD is based and the access control method for Ethernet. An alternative is to resend if there is no acknowledgment of receipt from the remote device.

Communications Controller A switching unit central to the implementation of host-based IBM S NA networks. Typically the network is built around a backbone of interlinked communications controllers to which host computers and Control Units (CUs) are attached.

Communications Manager An individual often underpaid and invariably overworked, dedicated to providing cost effective, ultimately flexible networking to users.

Communications Networks The UK's leading monthly magazine for networking professionals and decision makers.

Communications Server A specialized network server that provides access to external networks, communications facilities and hosts that cannot be directly connected to the LAN. Typically it will enable workstation users running appropriate workstation software, such as terminal emulation software, to access asynchronous communications links and typically modems attached to the communications server.

Communications Toolbox An extension of the Apple Macintosh operating system that provides protocol conversion and the drivers needed for communications tasks.

Concentration A technique used to get the most out of a composite multiplexer link. Usually a statistical multiplexer, or concentrator, is used to focus channel inputs on to the composite ink by removing the portions of the transmission carrying no data.

Concentrator A central chassis into which various modules, such as bridging, supervisory, 10BaseT and other peripheral cards are plugged.

Connection-oriented service The transport of packets of information from one network node to a destination node following an established network connection.

Connectionless Service The transport of a single datagram or packet of information from one network node to a destination node or multiple nodes without establishing a network connection.

Contention The process whereby multiple users make requests for transmission bandwidth across a transmission link but the pool of bandwidth is less than the aggregate amount of bandwidth the users could request between them. Contention is used to resolve which users gain access to the bandwidth. When this s applied to multiplexers, it is concerned with the multiplexer's ability to allow a number of channels to contend for transmission bandwidth that is less than the sum of all the channel rates.

Control point A program that manages an APPN network node and its resources, enabling communications to other control points in the network.

Converter A repeater that also converts from one media type to another, such as from fiber to copper. Often called a media adapter.

CPE (Customer Premises Equipment) Telecommunications- communications equipment, including PBXs and wiring, located in a user's premises.

CRC (Cyclic Redundancy Check) A method of detecting errors in the serial transmission of data. A CRC for a block of data is calculated before it is sent, and is then sent along with the data. A new CRC is calculated on the received data. If the new CRC does not match the one that has been sent along with the data then an error has occurred.

Cross-Connect An ATM switch usually comprising three functional areas. System control The central control unit, which also provides the management interface of the system; the ATM "fabric block" providing the system switching capacity; termination groups to provide the external interfaces and the functions of the ATM layer of the network node. Each of these functional system areas is configured according to the specified needs of the respective network node. Each functional area usually has its own monitoring and control units for safeguarding the high availability of the complete system.

Crosstalk Unwanted interference from another adjacent communications channel . The signal from the adjacent channel is inserted into the original communications channel.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection) The access method used in Ethernet. All nodes are attached to a single cable and contend equally for access to the transmission medium. if two nodes attempt to send data at the same time, they "sense" each other's signal and immediately stop sending. They will both try to send again after Waiting a random number of microseconds.

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) A method of network access not covered by OSI standards and used in AppleTalk networks.

CSU (Channel Service Unit) (1) In the US, data transmission equipment to repeat the signal from the carrier and ink to CPE. Vendors add value to CSUs by adding performance monitoring and management. (2) In Europe, CSUs are sold for their value features like diagnostics and performance monitoring. The basic repeating function is prd in the NTU (networking terminating unit). CSUs monitor quality on El, E2 or E3 circuits in terms of transmission and line loading.

CT1 First generation analog domestic cordless telephone (non-cellular).

CT2 Two-way digital cordless telephony technology, particularly relevant to cordless PBXs. In its public guise, it becomes a one way telepoint service now no longer available in the UK but prevalent in the Far East.

CT3 Ericsson's proprietary cordless telecommunications system.

CTI (Computer Telephone Integration) A generic name for the technology automatically relating computers and PABXs via applications such as ACD, power dialing, IVR and other customer facing or agent facing services. A so known by older, proprietary names CIT (Computer Integrated Telephony) and CSTA (Computer Supported Telephony Applications).
D