You need a 24x7 WLAN analysis solution to troubleshoot anytime and from anywhere. Preferably, from your office. Our support forums are a great first place to look if you have a support question. It is not used to connect user stations, but instead provides a synchronous signaling backbone that allows additional segments and repeaters to be connected to the network. It organizes a number of computers into a star topology without the use of repeaters Base FP segments can be up to meters long BaseT A specification of the IEEE committee for the implementation of 10 Mbit Ethernet on unshielded twisted pair wiring Broad Mbps broadband Ethernet specification using broadband coaxial cable. To guarantee proper signal timing, a 100BaseFX link exceed meters in length. Based on the IEEE standard BaseT A 100MB Ethernet specification using Level 5 UTP BaseT Mbps baseband Fast Ethernet specification using four pairs of Category 3, 4, or 5UTP wiring. To guarantee proper signal timing, a 100BaseT4 segment cannot exceed meters in length. Based on the IEEE standard BaseTX Mbps baseband Fast Ethernet specification using two pairs of either UTP or STP wiring. The first pair of wires is used to receive data, the second is used to transmit. To guarantee proper signal timing a 100BaseTX segment cannot exceed meters in length. Based on the IEEE standard BaseX Mbps baseband Fast Ethernet specification that refers to the 100BaseFX and 100BaseTX standards for Fast Ethernet over fiber-optic cabling. Based on the IEEE standard VG-AnyLAN Mbps Fast Ethernet and Token Ring media technology using four pairs of Category 3, 4, or 5 UTP cabling. This high-speed transport technology, developed by Hewlett-Packard, can be made to operate on existing 10BaseT Ethernet networks. Also called 24th channel signaling AAL ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs consist of two sublayers, CS and SAR, AALs differ on the basis of the source-destination timing used, whether they use DBR or VBR, and whether they are used for connection-oriented or connectionless mode data transfer. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic AAL2 ATM adaptation layer One of four AALs recommended by the ITU-T. AAL2 is used for connection-oriented services that support a variable bit rate, such as some isochronous video and voice traffic AAL ATM adaptation layer One of four AALs merger from two initially distinct adaptation layers recommended by the ITU-T. AAL supports both connectionless and connection oriented links, but is primarily used for the transmission of SMDS packets over ATM networks AAL5 ATM adaptation layer One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented, VBR services, and is used predominantly for the transfer of classic IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth over head and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability AARP AppleTalk Address Resolution Protocol. Protocol in the AppleTalk protocol stack that maps a data-link address to a network address AARP probe packets Packets transmitted by AARP that determine whether a randomly selected node ID is being used by another node in a nonextended AppleTalk network. If the node ID is not being used, the sending node uses that node ID. If the node ID is being used, the sending node chooses a different ID and sends more AARP probe packets ABM Asynchronous Balanced Mode. An HDLC and derivative protocol communication mode supporting peer-oriented, point-to- point communications between two stations, where either station can initiate transmission ABR available bit rate. QOS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delays, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the statue of the network and its capability to successfully deliver data. Compare with CBR, UBR, and VBR area border router. Router located on the border of one or more OSPF areas that connects those areas to the backbone network. ABRs are considered members of both the OSPF backbone and the attached areas. They therefore maintain routing tables describing both the backbone topology and the topology of the other areas AC Alternating Current. For example, the list can prevent packets with a certain IP address from leaving a particular interface on the router Access Method The type of Media Access Control method that a node uses to gain control of a network Accounting One of five categories of network management defined by ISO for Management management of OSI networks. Accounting management subsystems are responsible for collecting network data relating to resource usage. The primary SNA NCP. Sometimes abbreviated ACK ACR Allows cell rate. Parameter defined by the ATM Forum for ATM traffic management. ACR varies between the MCR and the PCR, and is dynamically controlled using congestion control mechanisms ACSE Association control service element. An OSI convention used to establish, maintain or terminate a connection between two applications Active Hub Multiported device that amplifies LAN transmission signals Active Monitor Device responsible for managing a Token Ring. A network node is selected to be the active monitor if it has the highest MAC address on the ring. The active monitor is responsible for management tasks such as ensuring that tokens are not lost or that frames do not circulate indefinitely Adapter Hardware that allows a computing device physical access to a network Adaptive Routing See dynamic routing ADCCP Advanced Data Communications Control Protocol Address A numerical designation that uniquely refers to a specific communication entity Addressed Call Mode that permits control signals and commands to Mode establish and terminate calls in V. For example, when routing IP over X. See also address resolution Address Mask Bit combination used to describe which portion of anaddress refers to the network or subnet and which partrefers to the host. For instance, translating an IP address to its given DNS name Address Resolution See ARP Protocol Address Space The range of possible unique addresses allowed by an addressing scheme Adjacency Relationship formed between selected neighboringrouters and end nodes for the propose of exchangingrouting information. Adjacency is based upon the useof a common media segment Adjacent Nodes In SNA, nodes that are connected to a given nodewith no intervening nodes In DECnet and OSI, nodes that share a common network segment in Ethernet, FDDI, or Token Ring networks Administrative Distance A rate of the trustworthiness of a routing information source. The higher the value, the lower the trustworthiness rating Admission Control See traffic policing ADPCM Adaptive differential pulse code modulation. Process by which analog voice samples are encoded into high-quality digital signals ADSU ATM DSU. Terminal adapter used to access an ATM network via an HSSI-compatible device. See also DSU Advertising Router process in which routing or service updates are sent at specified intervals so that other routers on the network can maintain lists of usable routes AEP AppleTalk Echo Protocol. Used to test connectivity between two AppleTalk nodes. One node sends a packet to another node and receives a duplicate, or echo, of that packet AFP AppleTalk Filing Protocol. The Apple proprietary specification for a network file system Agent An active process in a computer that is responsible for a certain type of activity when demanded by an outside entity In SNMP, the active process in a computing device that is responsible for determining the parameters defined in the MIB Management Information Base and reporting them on demand to a Console AIS Alarm indication signal. See also event and trap Alarm Indication Signal See AIS A-law The ITU-T companding standard used in the conversion between analog and digital signals in PCM systems. A-law is used primarily in European telephone networks and is similar to the North American mu-law standard. See also companding and mu-law Algorithm A set of rules and decision structures for actions in a specifically defined set of circumstances Alias A file whose sole purpose is to represent another file Alignment Error In IEEE networks, an error that occurs when the total number of bits of a received frame is not divisible by eight. Alignment errors are usually caused by frame damage due to collisions All-rings Explorer Packet See all-routes explorer packet All-routes Explorer Explorer Packet packet that traverses an entire SRB network, following all possible paths to a specific destination. Sometimes called all-rings explorer packet, See also explorer packet, local explorer packet, and spanning explorer packet ALOE Archaic. AppleTalk Low Overhead Encapsulation. A vendor-developed alternative to AURP, ALOE provides a mechanism to tunnel AppleTalk protocols inside IP packets, typically in WAN links Alphanumeric Referring to a group of printable characters that includes the letters of the alphabet in both upper and lower case, the numerals plus a limited group of additional symbols and punctuation marks AM Amplitude Modulation. Modulation technique whereby information is conveyed through the amplitude of the carrier signal. Compare with FM binary PAM. See also modulation Ambient Referring to a set of conditions that exist independently of the system of interest AMI Alternate mark inversion. Line-code type used on T1 and E1 circuits. In AMI, zeros are represented by 01 during each bit cell, and ones are represented by 11 or 00, alternately, during each bit cell. AMI requires that the sending device maintain ones density. Ones density is not maintained independent of the data stream. Sometimes called binary coded alternate mark inversion. See also ones density Amp Ampere. A standard unit of measurement for electrical current flow Amplitude In the terminology of wave motion, the height of the wave. Amplitude is usually measured from a reference point of In electrical waves, amplitude is typically expressed in volts Analog Referring to a system or component that uses a system of measurement, response or storage in which values are expressed a s a magnitude using a continuous scale of measurement Analog Transmission Signal transmission over wires or through the air in which information is conveyed through variation of some combination of signal amplitude, frequency, and phase Anomaly An unusual instance or circumstance ANSI American National Standards Institute. The principle group in the US. Technology that allows a server to be attached to CDDI or FDDI without requiring the reconfiguration of applications or network protocols. APaRT recognizes specific data link layer encapsulation packet types and, when these packet types are transferred from one medium to another, translates them into the native format of the destination device API Application Programming Interface. A set of tools and procedures provided by the programmer of an application so that other programmers can control, exchange data with, or extend the functionality of an application Apollo Domain Proprietary network protocol suite developed by Apollo Computer for communication on proprietary Apollo networks APPC Advanced Program-to-Program Communication. IBM SNA system software that allows high-speed communication between programs on different computers in a distributed computing environment. APPC establishes and tears down connections between communicating programs, and consists of two interfaces, a programming interface and a data-exchange interface. The former replies to requests from programs requiring communication; the latter establishes sessions between programs. APPC runs on LU devices. This layer provides services to application processes such as electronic mail, file transfer, and terminal emulation that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners and the resources required to connect with themsynchronizes cooperating applications, and agreement on procedures for error recovery and control of data integrity. Corresponds roughly with the transaction services layer in the SNA model. See also data link layer, network layer, physical layer, presentation layer, session layer, and transport layer APPN Advanced Peer-to-Peer Networking. Enhancement to the original IBM SNA architecture. APPN handles session establishment between peer nodes, dynamic transparent route calculation, and traffic prioritization for APPC traffic. Also called high-performance routing. See also APPN ARA AppleTalk Remote Access. Protocol that provides Macintosh users direct access to information and resources at a remote AppleTalk site Architecture The sum total of all of the specifications, protocols and implementations that define a particular networking system Archive A storage of infrequently-used or historical data ARCnet Attached Resource Computer Network. A Mbps token-bus LAN developed in the late s and early s by Datapoint Corporation Area Logical set of network segments either CLNS- DECnet- OSPF-based and their attached devices. Areas are usually connected to other areas via routers, making up a single autonomous system. See also autonomous system ARM Asynchronous response mode, HDLC communication mode involving one primary station and at least one secondary station, where either the primary or one of the secondary stations can initiate transmissions. See also primary station and secondary station ARP Address Resolution Protocol. The protocol for mapping IP addresses to physical addresses such as Ethernet or Token Ring ARPA Advanced Research Projects Agency, Research and development organization that is part of DoD. ARPA is responsible for numerous technological advances in communications and networking. ARPA evolved in DARPA, and then back into ARPA again in See also DARPA ARPANET Advanced Research Projects Agency Network. Landmark packet-switching network established in ARPANET was developed in the s by BBN and funded by ARPA and later DARPA. It eventually evolved into the Internet. The term ARPANET was officially retired in ARQ Automatic repeat request. Communication technique in which the receiving device detects errors and requests retransmission AS See autonomous system ASBR Autonomous system boundary router. ABR located between an OSPF autonomous system and a non-OSPF network. ASBRs run both OSPF and another routing protocol, such as RIP, ASBRs must reside on a nonstub OSPF area ASCII Referring to binary standard 7-bit character system that includes the alphanumeric characters and printer control codes ASDSP AppleTalk Secure Data Stream Protocol. An encrypted version of ADSP used by AOCE ASIC Application-Specific Integrated Circuit. A custom chip for a specific application ASLM Apple Shared Library Manager ASN. In SNMP, the language used to describe data managed by the MIB Associative Memory Memory that is accessed based on its contents, not on its memory address. Sometimes called content addressable memory CAM AST Automatic spanning tree. Function that supports the automatic resolution of spanning trees in SRB networks, providing a single path for spanning explorer frames to traverse from a given node in the network to another. AST is based on the IEEE standard ASTA Advanced Software Technology and Algorithms. Component of the HPCC program intended to develop software and algorithms for implementation on high-performance computer and communications systems. See also HPCC Asymmetry In networking, a system in which the relationship between two entities is inherently unequal, with each entity restricted to a set of operations and prerogatives defined by its role in the relationship Asynchronous A system of communication in which each discreet delivery of information establishes its own timing impulse rather than having to conform to the timing impulse of previous deliveries Asynchronous Term describing digital signals that are transmitted without precise clocking. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits called start and stop bits that designate the beginning and end of each character. Compare with Isochronous transmission, plesiochronous transmission, and synchronous transmission AT commands Transmission A set of commands that control a modem or alter its characteristics ATDM Asynchronous time-division multiplexing. Method of sending information that resembles normal TDM, except that time slots are allocated as needed rather than preassigned to specific transmitters. Compare with FDM, Statistical multiplexing, and TDM ATM Asynchronous Transfer Mode. A broadband transmission system using 53-octet packets over a cell-switched network at speeds up to GBPS ATP AppleTalk Transaction Protocol. Generally expressed in decibels Attribute Configuration data that defines the characteristics of database objects such as the chassis, cards, ports, or virtual circuits of a particular device. Attributes might be preset or user-configurable. On a LightStream ATM switch, attributes are set using the configuration program or CLI commands AUI Attachment unit interface. IEEE interface between an MAU and a NIC network interface card. Also called transceiver cable AURP AppleTalk Update-Based Routing Protocol. Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique 16-bit number by the IANA. Sometimes abbreviated AS Autoreconfiguration Process performed by nodes within the failure domain of a Token Ring network. Nodes automatically perform diagnostics in an attempt to reconfigure the network around the failed areas Average Rate The average rate, in kilobits per second kbpsat which a given virtual circuit will transmit B8ZS Binary 8-zero substitution. Line-code type, used on T1 and E1 circuits, in which a special code is substituted whenever 8 consecutive zeros are sent through the link. This code is then interpreted at the remote end of the connection. This technique guarantees ones density independent of the data stream. Sometimes called bipolar 8-zero substitution. See also ones density Back End Node or software program that provides services to a front end. A device that links together dissimilar wire types and attempts to minimize any negative effects to the signal that would normally result from the dissimilarity Band In analog communications, the range of frequencies over which a communication system operates Bandwidth In analog communications, the difference between the highest and lowest frequencies available in the band. In digital communications, bandwidth is loosely used to refer to the information-carrying capacity of a network or component of a network Bandwidth Allocation See Bandwidth reservation Bandwidth Reservation Process of assigning bandwidth to users and applications served by a network. Involves assigning priority to different flows of traffic based on how critical and delay-sensitive they are. This makes the best use of available bandwidth, and if the network becomes congested, lower-priority traffic can be dropped. Sometimes called bandwidth allocation. See also call priority BARRNet Bay Area Regional Research Network. Regional network serving the San Francisco Bay Area. The BARRNet backbone is composed of four University of California campuses Berkeley, Davis, Santa Cruz, and San FranciscoStanford University, Lawrence Livermore National Laboratory, and NASA Ames Research Center. BARRNET is now part of BBN Planet Base address The lowest address available in an address range Baseband A communication system in which only one signal is carried at any one time Baud Unit of signaling speed equal to the number of discrete signal elements transmitted per second. Baud is synonymous with bits per second bpsif each signal element represents exactly 1 bit Baud Rate The number of voltage or frequency transitions per second BBN Bolt, Beranek, and Newman, Inc. High-technology company located in Massachusetts that developed and maintained the ARPANET and later, the Internet, core gateway system BBN Planet Subsidiary company of BBN that operates a nationwide Internet access network composed in part of the former regional networks BARRNET, NEARNET, and SURAnet Bc Committed Burst. Negotiated tariff metric in Frame Relay internetworks. The maximum amount of data in bits that a Frame Relay internetwork is committed to accept and transmit at the CIR B Channel Bearer channel. In ISDN, a full-duplex, 64-kbps channel used to send user data. Compare to D channel, E channel, and H channel Be Excess Burst. The number of bits that a Frame Relay internetwork will attempt to transmit after Bc is accommodated. Be data is, in general, delivered with a lower probability than Bc data because Be data can be marked as DE by the network Beacon Frame from a Token Ring or FDDI device indicating a serious problem with the ring, such as a broken binary. A beacon frame contains the address of the station assumed to be down BECN Backward explicit congestion notification. Bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN bit set can request that higher-level protocols take flow control action as appropriate. Compare with FECN Bellcore Bell Communications Research. Organization binary performs research and binary on behalf of the RBOCs Bellman-Ford Routing Algorithm See distance vector routing algorithm Benchmark A test performed t compare a computer process in one set of circumstances to another BER Bit error rate. The ratio of received bits that contain errors Binary encoding rules. Rules for encoding data units described in the ISO ASN. Interdomain routing protocol that replaces EGP. BGP exchanges reachability information with other BGP systems. It is defined by Signal BGP4 BGP Version Version 4 of the predominant interdomain routing protocol used on the Internet. BGP4 supports CIDR and uses route aggregation mechanisms to reduce the size of routing tables BIGA Bus Interface Gate Array. Technology that allows the Catalyst to receive and transmit frames from its packet-switching memory to its MAC local buffer memory without the intervention of the host processor Big-endian Method of storing or transmitting data in which the most significant bit or byte is presented first. Clocking information is embedded into and recovered from the synchronous data stream without the need for separate clocking leads. The biphase signal contains no direct current energy Bipolar Electrical characteristic denoting a circuit with both negative and positive polarity. Contrast with unipolar BISDN Broadband ISDN. ITU-T communication standards designed to handle high-bandwidth applications such as video. BISDN currently uses ATM technology over SONET-based transmission circuits to provide data rates from to Mbps and beyond Bit The basic unit of data representation in digital computers. Low-cost, low-speed academic network consisting primarily of IBM mainframes and bps leased lines. BITNET is now a part of CREN. See also CREN BITNET III Dial-up service providing connectivity for members of CREN Bit-oriented Protocol Class of data link layer communication protocols that can transmit frames regardless of frame content. Compared with byte-oriented protocols, bit-oriented protocols provide full-duplex operation and are more efficient and reliable. Compare with byte-oriented protocol Bit pattern A sequence of bits that has a specific purpose or meaning Bit rate The rate at which bits are transmitted or received during communication, expressed as the number bits in a given amount of time, usually one second Bitmap A data structure that uses bits to represent the attributes of an object that is not character-based Black Box A device that performs a function using mechanisms that are unimportant or impossible to understand Black Hole Routing term for an area of the internetwork where packets enter, but do not emerge, due to adverse conditions or poor system configuration within a portion of the network Block The basic unit of storage on a computer disk Blocking In a switching system, a condition in which no paths are available to complete a circuit. The term is also used to describe a situation in which one activity cannot begin until another has been completed Block Multiplexer I Channel BM-style channel that implements the FIPS-60 channel, AUS. This channel is also referred to as OEMI channel and block mux channel BNC Bayonet "N" Connector The locking connector type used in 10Base2 Thin Ethernet Any connector similar to the type used by 10Base2 for CATV, and other electronic uses BNN Boundary network node. In SNA terminology, a subarea node that provides boundary function support for adjacent peripheral nodes. This support includes sequencing, pacing, and address translation Board A printed circuit and the substrate on which it lies BOC Bell operating company. An IP protocol used by diskless workstations to receive boot information from a boot server Boot PROM Boot programmable read-only memory. Chip mounted on a printed circuit board used to provide executable boot instruction to a computer device Border Gateway Router that communicates with routers in other autonomous systems Boundary Function Capability of SNA subarea nodes to provide protocol support for attached peripheral nodes. Typically found in IBM devices BPDU Bridge protocol data unit. Spanning-Tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network BPS Bits Per Second. A commonly-used measure of the rate of data transmission that specifies the number of bits that are transmitted in one second. May be prefixed with multipliers such as K, M, and G which indicate rates of thousands, millions and billions of bits per second BRI Basic Rate Interface. Described in the IEEE standard. See also IEEE Bridge Number Number that identifies each bridge in an SRB LAN. Parallel bridges must have different bridge numbers Bridge Static Filtering Process in which a bridge maintains a filtering database consisting of static entries. Each static entry equates a MAC destination address with a port that can receive frames with this MAC destination address and a set of ports on which the frames can be transmitted. Defined in the IEEE standard Broadband A transmission system capable of carrying many channels of communication simultaneously by modulating them on one of several carrier frequencies Broadcast An information transmission that is intended to be interpreted by all entities capable of receiving it Broadcast Address Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all ones. Compare with multicast address and unicast address Broadcast Domain The set of all devices that will receive broadcast frames originating from any device within the set. Broadcast domains are typically bounded by routers because routers do not forward broadcast frames Broadcast Search Propagation of a search request to all network nodes if the location of a resource is unknown to the requester Broadcast Storm Undesirable network event in which many broadcasts are sent simultaneously across all network segments. A broadcast storm uses substantial network bandwidth and, typically, causes network time-outs Brouter A device that incorporates the functionality of a bridge and a router in a single unit BSC Binary synchronous communication. Character-oriented data link layer protocol for half-duplex applications. Often referred to simply as bisync BSD Berkeley Software Distribution. For VBR connections, BT determines the size of the maximum burst of contiguous cells that can be transmitted Buffer A temporary memory storage area for information Bug A flaw in a software program Bundled Refers to the practice of automatically including an additional application or capability in the sale or delivery of a computing component that is not ordinarily associated with that component BUS Broadcast and unknown server. Multicast server used in ELANs that is used to flood traffic addressed to an unknown destination, and to forward multicast and broadcast traffic to the appropriate clients Bus A type of network topology in which nodes are connected alonga continuous path that is not a closed circuit. Also refers to acommunications channel used by a single computer such asNubus, SCSI, etc Bus and Tag Channel IBM channel, developed in the s, incorporating copper multiwire technology. Replaced by the EXCON channel. See also ESCON channel and parallel channel Bus Topology Linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations. Compare with ring topology, star topology, and tree topology Bypass Mode Operating mode on FDDI and Token Ring networks in which an interface has been removed from the ring Bypass Relay Allows a particular Token Ring interface to be shut down and thus effectively removed from the ring Byte A group of 8 bits Byte-oriented Protocol Class of data-link communications protocols that use a specific character from the user character set to delimit frames. These protocols have largely been replaced by bit-oriented protocols. Compare with bit-oriented protocol Byte Reversal Process of storing numeric data with the least-significant byte first. Used for integers and addresses on devices with Intel microprocessors Byte A group of 8 bits Cable The transmission media of a network Cable Range Range of network numbers that is valid for use by nodes on an extended AppleTalk network. The cable range value can be a single network number or a contiguous sequence of several network numbers. Node addresses are assigned based on the cable range value Cache A group of memory locations set aside for temporary storage ofdata, especially frequently-used data or data needing high speedretrieval by the CPU Call Admission Control Traffic management mechanism used in ATM networks thatdetermines whether the network can offer a path with sufficient bandwidth for a requested VCC Call Priority Priority assigned to each origination port in circuit-switched systems. This priority defines the order in which calls are reconnected. Call priority also defines which calls can or cannot be placed during a bandwidth reservation Call Setup Time The time required to establish a switched call between DTE devices CAM Content-addressable memory. Category 1 cabling is used for telephone communications and is not suitable for transmitting data. Compare with Category 2 cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling. Category 2 cabling is capable of transmitting data at speeds up to 4 Mbps. Compare with Category 1 cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling. Category 3 cabling is used in 10Base T networks and can transmit data at speeds up to 10 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 4 cabling, and Category 5 cabling. Category 4 cabling is used in Token Ring networks and can transmit data at speeds up to 16 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 3 cabling, and Category 5 cabling. Category 5 cabling is used for running CDDI and can transmit data at speeds up to Mbps Compare with Category 1 cabling, Category 2 cabling, Category 3 cabling, and Category 4 cabling. The Internet is a prominent example of a catenet CATV Cable television. Communication system where multiple channels of programming material are transmitted to homes using broadband coaxial cable. Formerly called Community Antenna Television CBDS Connectionless Broadband Data Service. European high-speed, packet-switched, datagram-based WAN networking technology. Similar to SMDS CBR Constant bit rate. CBR is used for connections that depend on precise clocking to ensure undistorted delivery CCITT Consultative Committee for International Telegraph and Television and Telephone. International organization responsible for the development of communications standards. Now called the ITU-T CCS Common Channel Signaling. Signaling system used in telephone networks that separates signaling information from user data. A specified channel is exclusively designated to carry signaling information for all other channels in the system CD Carrier Detect. Signal that indicates whether an interface is active. Also, a signal generated by a modem indicating that a call has been connected CDDI Copper Distributed Data Interface. Implementation of FDDI protocols over STP and UTP cabling. CDDI transmits over relatively short distance about metersproviding data rates of 100Mbps using a dual-ring architecture to provide redundancy. Based on the ANSI Twisted-Pair Physical Medium Dependent TPPMD standard CDEV The designation of a Control Panel Device in Macintosh System 6and earlier obsolete CDPD Cellular Digital Packet Data. Open standard for two-way wireless data communication over high-frequency cellular telephone channels. Allows data transmissions between a remote cellular link and a NAP. Operates at Kbps CDVT Cell delay variation tolerance. In CBR transmissions, determines the level of jitter that is tolerable for the data samples taken by the PCR CEDI Cayman Encapsulated DDP in IP. An Apple Talk tunneling protocol developed by Cayman Cell The basic unit for ATM Switching and multiplexing. Cells contain identifiers that specify the data stream to which they belong. Each cell consists of a 5-byte header and 48 bytes of payload. See also cell relay Cell Loss Priority See CLP Cell Relay Network technology based on the use of small, fixed-size packets, or cells. Because cells are fixed-length, they can be processed and switched in hardware at high speeds. Cell relay is the basis for many high-speed network protocols including ATM, IEEEand SMDS Cells Per Second Abbreviated cps Cellular Radio Technology that uses radio transmissions to access telephone-company networks. Association of the 26 European PTTs that recommends communication specifications to the ITU-T CERTnet California Education and Research Federation Network. CERFnet was founded in by the San Diego Supercomputer Center and General Automics and is funded by the NSF Chaining SNA concept in which RUs are grouped together for the propose of error recovery Channel A communication path. The individual channels or groups of channels connect to different destinations. Supports DDR, Frame Relay, and X Also referred to as fractional T1. Compare with channelized E Channel Service Unit See CSU CHAP Challenge Handshake Authentication Protocol. Security feature supported on lines using PPP encapsulation that prevents unauthorized access. CHAP does not itself prevent unauthorized access, it merely identifies the remote end. The router or access server than determines whether that user is allowed access. Compare to PAP Character A symbol such as a letter, number or punctuation mark that canbe arranged to represent higher units of meaning, such as wordsand sentences The group of bits that represents such a symbol Chat Script String of text that defines the login "conversation" that occurs between two systems. Consist of expect-send pairs that define the string that the local system expects to receive from the remote system and what the local system should send as a reply Cheapernet Industry term used to refer to the IEEE Base2 standard or the cable specified in that standard. See also 10Base2, Ethernet, and IEEE Checksum The result of a mathematical operation that uses the binary representation of a group of data as its basis, usually to check the integrity of the data Choke Packet Packet sent to a transmitter to tell it that congestion exists and that it should reduce its sending rate CIA See classic IP over ATM CICNet Regional network that connects academic, reserach, nonprofit, and commercial organizations in the Midwestern United States. Founded inCICNet was a part of the NSF NET and was funded by the NSF until the NSFNET dissolved in See also NSFNET CICS Customer Information Control System. IBM application subsystem allowing transactions entered at remote terminals to be processed concurrently by user applications CIDR Classless interdomain routing. Technique supported by BGP4 and based on route aggregation. CIDR allows routers to group routes together in order to cut down on the quantity of routing information carried by the core routers. With CIDR, several IP networks appear to networks outside the group as a single, larger entity CIR Committed information rate. The rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated tariff metrics Circuit Any electrical pathway An arrangement of electrical andelectronic devices and the conductive paths between them Circuit Group Grouping of associated serial lines that link two bridges. If one of the serial links in a circuit group is in the spanning tree for a network, any of the serial links in the circuit group can be used for load balancing. This load-balancing strategy avoids data ordering problems by assigning each destination address to a particular serial link Circuit Switching Switching system in which a dedicated physical circuit path must exist between sender and receiver for the duration of the "call. Circuit switching can be contrasted with contention and token passing as a channel-access method, and with message switching and packet switching as a switching technique Classic IP Over ATM Specification for running IP over ATM in a manner that takes full advantage of the features of ATM. Defined in RFC Sometimes called CIA CLAW Common Link Access for Workstations. Typically, the client computerdrives the relationship and uses a resource of the servercomputer CLNP Connectionless Network Protocol. OSI network layer protocol that does not require a circuit to be established before data is transmitted. See also CLNS CLNS Connectionless Network Service. OSI network layer service that does not require a circuit to be established before data is transmitted. CLNS routes messages to their destinations independently of any other messages. See also CLNP CLP Cell loss priority. Field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested. Typically, an IBM or device CMI Coded mark inversion. ITU-T line coding technique specified for STS-3c transmissions. Also used in DS-1 systems CMIP Common Management Information Protocol CMIS Common Management Information Services. OSI network management service interface created and standardized by ISO for the monitoring and control of heterogeneous networks. See also CMIP CMNS Connection-Mode Network Service. See also CMT Connection management. FDDI process that handles the transition of the ring through its various states off, active, connect, and so onas pam by the ANSI X3T9. Local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs Coaxial cable An electrical cable in which the conductors share a common axis CODEC Coder-decoder. Device that typically uses PCM to transform analog signals into a digital bit stream and digital signals back into analog Coding Electrical techniques used to convey binary signals Collapsed Backbone Nondistributed backbone in which all network segments are interconnected by way of an internetworking device. A collapsed backbone might be a virtual network segment existing in a device such as a hub, a router, or a switch Collision In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device impact and are damaged when they meet on the physical media. See also Collision domain Collision Avoidance A Media Access Control MAC method in which any node maytake control of the network after taking certain steps to insure thatthe cable is not in use or about to be used by another node Collision Detection A MAC method in which any node may take control of the networkwhen it is not in use by another node. While transmitting, stationscontinue to listen for incoming signals collisions and emit a jamming signal to notify all other stations of the collision Collision Domain Pam Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges and routers do not. See also collision Common Carrier Licensed, private utility company that supplies communication services to the public at regulated prices Communication Transmission of information Communication Controller In SNA, a subarea node such as an IBM device thatcontains an NCP Communication Server Communications processor that connects asynchronous devicesto a LAN or WAN through network and terminal emulation software. Performs only asynchronous routing of IP and IPX. Compare with access server Communications Line The physical link such as wire or a telephone circuit that connects one or more devices to one or more other devices Community In SNMP, a logical group of managed devices and NMSs in the same administrative domain Community String Text string that acts as a password and is used to authenticate messages sent between a management station and a router containing a SNMP agent. The community string is sent in every packet between the manager and the agent Companding Contraction derived from the opposite processes of compression and expansion. Part of the PCM process whereby analog signal values are logically rounded to discrete scale-step values on a nonlinear scale. The decimal step number is then coded in its binary equivalent prior to transmission. The process is reversed at the receiving terminal using the same nonlinear scale. Compare with compression and expansion. See also a-law and mu-law Component An indivisible unit of functionality, usually embodied in hardware Compression An alteration performed on a unit of information intended to increase it density during storage of transmission Concentrator A synonym for a multi-port repeater that may also perform bridging and routing functions Conductor The current-carrying component of a transmission cable, typicallya copper wire Configuration Management One of five categories of network management of OSI networks. Configuration management subsysems are responsible for detecting and determining the state of a network. See also account management, fault management, performance management, and security management Congestion Traffic in excess of network capacity Connection-Oriented In data networks, a type of computer relationship in which the network equipment constructs a circuit between the two devices for the duration of their relationship. Once the circuit is established, the devices pass information back and forth through the circuit without regard to their physical addresses. The circuit may be physical or virtual Connectionless A type of relationship between two devices where each information packet must contain the address of the partner device. Indication of how an upper-layer protocol requires that a lower-layer protocol treat its messages. In SNA subarea routing, COS definitions are used by subarea nodes to determine the optimal route to establish to given session. A COS definition comprises a virtual route number and a transmission priority field. Also called TOS type of service Corporation for Open Systems. Organization that promulgates the use of OSI protocols through conformance testing, certification, and related activities COSINE Cooperation for Open Systems Interconnection Networking in Europe. European project financed by the European Community EC to build a communication network between scientific and industrial entities in Europe. The project ended in Cost Arbitrary value, typically based on hop count, media bandwidth, or other measures, that is assigned by a network administrator and used to compare various paths through an internetwork environment. Cost values are used by routing protocols to determine the most favorable path to a particular destination: the lower the cost, the better the path. Sometimes called path cost. See also routing metric Count to Infinity Problem that can occur in routing algorithms that are slow to converge, in which routers continuously increment the hop count to particular networks. Typically, some arbitrary hop-count limit is imposed to prevent this problem CP Control point. In SNA networks, element that identifies the APPN networking components of a PU node, manages device rresources, and can provide services to other devices. In APPN, CPs are able to communicate with logically adjacent CPs by way of CP-to-CP sessions. See also EN and NN CPCS Common part convergence sublayer. One of the two sublayers of any AAL. The CPCS is service-independent and is further divided into the CS and the SAR sublayers. The CPCS is responsible for preparing data for transport across the ATM network, including the creation of the 48-byte payload cells that are passed to the ATM layer. See also AAL, ATM layer, CS, SAR, and SSCS CPE Customer premises equipment. Terminating equipment, such as terminals, telephones, and modems, supplied by the telephone company, installed at customer sites, and connected to the telephone company network CPI-C Common Programming Interface for Communications. Platform-independent API developed by IBM and used to provide portability in APPC applications. See also APPC CPS Cells per second CPU Central Processing Unit. Inmany instances, the computer becomes completely unusable andmust be restarted before activity can resume CRC Cyclic Redundancy Check. A method of insuring data integritywhere a calculation is performed using the binary representationof the data itself as the basis of the calculation. The CRC is thenumerical result of this calculation and is held separately from thedata. The integrity of the data is checked by calculating a newCRC. The result of a merger of BITNET and CSNET. CREN is devoted to providing Internet connectivity to its members, which include the alumni, students, faculty, and other affiliates of participating educational and research institutions, via BITNET III. See also BITNET, BITNET III, and CSNET Crosstalk In electronic signaling, an error condition caused when the signal from one circuit causes a disturbance to the signal of thenearby circuit CS Convergence sublayer. One of the two sublayers of the AAL CPCS, responsible for padding and error checking. PDUs passed from the SSCS and appended with a 8-byte trailer for error checking and other control information and padded, if necessary, so that the length of the resulting PDU is divisible by These PDUs are then passed to the SAR sublayer of the CPCS for further processing. See also AAL, CPCS, SAR, and SSCS CSA Canadian Standards Association. Agency within Canada that certifies products that conform to Canadian national safety standards CSLIP Compressed Serial Link Internet Protocol. Extension of SLIP that, when appropriate, allows just header information to be sent across a SLIP connection, reducing overhead and increasing packet throughput on SLIP lines. Media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. Large internetwork consisting primarily of universities, research institutions, and commercial concerns. CSNET merged with BITNET to form CREN CSNP Complete sequence number PDU. PDU sent by the designated router in an OSPF network to maintain database synchronization CSU Channel service unit. Digital interface device that connects end-user equipment to the local digital telephone loop. See also DSU CTS Clear To Send. Cornerstone of the IBM strategy to reduce the number of protocols on networks. A device using cut-through packet switching reads, processes, and forwards packets as soon as the destination address is looked up, and the outgoing port determined. Also known as on-the-fly packet switching. Contrast with store and forward packet switching DAC Dual-attached concentrator. FDDI or CDDI concentrator capable of attaching to both rings of an FDDI or CDDI network. It can also be dual-homed from the master ports of other FDDI or CDDi concentrators Daemon In the UNIX operating system, a computing process that, oncestarted, is not under user control, but continues to run in the background. Daemons usually perform a particular purpose on demand, such as supplying information to another processor. An example in AppleTalk networking is the atalkad daemon, which supplies AppleTalk tunneling information to routers on request Daisy Chain In LocalTalk, a daisy chain is made by linking LocalTalkconnectors together with patch cord. In telephony, a daisy chainrefers to the method of linking a series of wall outlets togetherwith twisted pair cabling rather than the normal practice of connecting the wall outlets to a central location home run. In telephony, "daisy chaining" is equivalent to the "backbone" method of LocalTalk construction DAL Data Access Language. A data base metalanguage designed byApple. A superset of SQL DARPA Defense Advanced Research Projects Agency. Evolved from ARPA, and then, fromback to ARPA DARPA Internet Obsolete term referring to the Internet. See Internet DAS Dual attachment station. Device attached to both the primary and the binary FDDI rings. Dual attachment provides redundancy for the FDDI ring; if the primary ring fails, the station can wrap the primary ring to the secondary ring, isolating the failure and retaining ring integrity. Also known as a Class A station DAT Digital Audio Tape. A type of storage media used for the backupof computing data Data Information represented in a format readable by a computer Data Base A collection of data that can be selectively retrieved by a type ofapplication knows as a Data Base Management System Data Flow Control Layer Layer 5 of the SNA architectural model. This layer determines and manages interactions between session partners, particularly data flow. Corresponds to the session layer of the OSI model. See also data link control layer, path control layer, physical control llayer, presentation services layer, transaction services layer, and transmission control layer Datagram Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit. IP datagrams are the primary information units in the Internet. This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: The MAC sublayer and the LLC sublayer. Sometimes simply called link layer. Roughly corresponds to the data link control layer of the SNA model. See also application layer, LLC, MAC, network layer, physical layer, presentation layer, session layer, and transport layer Data Link Protocol The protocol that controls the network signaling and receivinghardware, performing data integrity checks and formatting information according to the rules of the data link Data Sink Network equipment that accepts data transmissions Data Stream All data transmitted through a communications line in a single read or write operation dB Decibels DB Connector Database bus connector. Type of connector used to connect serial and parallel cables to a data bus. DB connector names are of the format DB-x, where x represents the number of wires within the connector. Each line is connected to a pin on the connector, but in many cases, not all pins are assigned a function. Now called DISA DCC Data Country Code. One of two ATM Address formats developed by the ATM Forum for use by private networks. Adapted from the subnetwork model of addressing in which the ATM layer is responsible for mapping network layer addresses to ATM Addresses. See also ICD DCE Distributed Computing Environment D Channel Data channel. Full-duplex, 16-kbps BRI or 64-kbps PRI ISDN channel. Compare to B channel, E channel, and H channel In SNA, a device that connects a processor and main storage with peripherals DDM Distributed Data Management. Software in an IBM SNA environment that provides peer-to-peer communication and file sharing. One of three SNA transaction services. See also DIA and SNADS DDN Defense Data Network. DDN is operated and maintained by DISA. See also DISA and MILNET DDP Datagram Delivery Protocol. Apple Computer network layer protocol that is responsible for the socket-to-socket delivery of datagrams over an AppleTalk internetwork DDR Dial-on-demand routing. Technique whereby a Cisco router can automatically initiate and close a circuit-switched session as transmitting stations demand. The router spoofs keepalives so that end stations treat the session as active. DDR permits routing over ISDN or telephone lines using an external ISDN terminal adapter or modem DE Discard eligible. See tagged traffic Deadlock Unresolved contention for the use of a resource In APPN, when two elements of a process each wait for action by or a response from the other before they resume the process Decay A loss in the clarity or readability of an electronic signal caused bythe interaction of the signal with its carrier and electrical environment Decibel A measurement that refers to the ratio of the strength of one signalto another. Decibels are commonly used to express signal lossor the relationship of the signal strength to ambient noise DECnet Group of communications products including a protocol suite developed and supported by Digital Equipment Corporation. Phase IV Prime supports inherent MAC addresses that allow DECnet nodes to coexist with systems running other that have MAC address restrictions. See also DNA DECnet Routing Signal routing scheme introduced by Digital Equipment Corporation in DECnet Phase III. In DECnet Phase V, DECnet completed its transition to OSI routing protocols ES-IS and IS-IS Decryption The reverse application of an encryption algorithm to encrypted data, thereby restoring that data to its original, unencrypted state. See also encryption Dedicated LAN Network segment allocated to a single device. Used in LAN switched network topologies Dedicated Line Communications line that is indefinitely reserved for transmissions, rather than switched as transmission is required. See also leased line De Facto Standard Standard that exists by nature of its widespread use. Compare with de jure standard. See also standard Default Route Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table De Jure Standard Standard that exist because of its approval by an official standards body. Compare with de facto standard. See also standard Delay The time between the initiation of a transaction by a sender and the first response received by the sender. Also, the time required to move a packet from source to destination over a given path Demand Priority Media access method used in 100VG-AnyLAN that uses a hub that can handle multiple transmission requests and can process traffic according to priority, making it useful for servicing time-sensitive traffic such as multimedia and video. Demand priority eliminates the overhead of packet collisions, collision recovery, and broadcast traffic typical in Ethernet networks. See also 100VG-AnyLAN Demarc Demarcation point between carrier equipment and CPE Demodulation Process of returning a modulated signal to its original form. Modems perform demodulation by taking an analog signal and returning it to its original digital form. See also modulation Demultiplexing The separating of multiple input streams that have been multiplexed into a common physical signal back into multiple output streams. See also multiplexing Dense Mode PIM See PIM dense mode DES Data Encryption Standard. Standard cryptographic algorithm developed by the US Designated Bridge The bridge that incurs the lowest path cost when forwarding a frame from a segment to the route bridge Designated Router OSPF router that generates LSAs for a multiaccess network and has other special responsibilities in running OSPF. Each multiaccess OSPF network that has at least two attached routers has a designated router that is elected by the Signal Hello protocol. The designated router enables a reduction in the number of adjacencies required on a multiaccess network, which in turn reduces the amount or routing protocol traffic and the size of the topological database Desktop In the Macintosh user interface, the background image of theFinder on which the icons for applications, directories and datafiles are displayed Destination Address Address of a network device that is receiving data. See also source address Deterministic Load Distribution Technique for distributing traffic between two bridges binary a circuit group. Guarantees packet ordering between source-destination pairs and always forwards traffic for a source-destination pair on the same segment in a circuit group for a given circuit-group configuration Device See node Device Driver Software that acts as an intermediary between a CPU and aperipheral device. The CPU sends a command to the devicedriver, which translates that command into a command meaningful to the peripheral device DFT Distributed Function Terminal DIA Document Interchange Architecture. Defines the protocols and data formats needed for the transparent interchange of documents in an SNA network. German national standards organization DIN Connector Deutsche Industrie Norm connector. Multipin connector used in some Macintosh and IBM PC-compatible computers, and on some network processor panels Directed Search Search request sent to a specific node known to contain a resource. A directed search is used to determine the continued existence of the resource and to obtain routing information specific to the node. See also broadcast search Direct Memory Access See DMA Directory Services Services that help network devices locate service providers DISA Defense Information Systems Agency. See also DDN Discovery Architecture APPN software that enables a machine configured as an APPN EN to automatically fine primary and backup NNs when the machine is brought onto an APPN network Discovery Mode Method by which an AppleTalk interface acquires information about an attached network from an operational node and then uses this information to configure itself. Also called dynamic configuration Distance Vector Routing Algorithm Class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree. Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops, but are computationally simpler than link state routing algorithms. Also called Bellman-Ford routing algorithm. See also link state routing algorithm and SPF Distortion A change in a electronic signal that occurs when different frequen-cy components of the signal decay at different rates. In a signalmade up of many frequency components such as a squarewavethe higher frequency components of a signal typicallydecay faster than the lower frequency components Distortion Delay Problem with a communication signal resulting from nonuniform transmission speeds of the components of a signal through a transmission medium. Also called group delay DLCI Data-link connection identifier. Value that specifies a PVC or SVC in a Frame Relay network. In the basic Frame Relay specification, DLCIs are locally significant connected devices might use different values to specify the same connection. In the LMI extended specification, DLCIs are globally significant DLCIs specify individual end devices. See also LMI DLL Dynamically Linked Libraries. DLSw uses SSP Switch-to-Switch Protocol instead of SRB, eliminating the major limitations of SRB, including hop-count limits, broadcast and unnecessary traffic, timeouts, lack of flow control, and lack of prioritization schemes. See also SRB, and SSP Switch-to-Switch Protocol DLU Dependent LU. An LU that depends on the SSCP to provide services for establishing session with other LUs. See also LU and SSCP DLUR Dependent LU Requester. The DLUR component resides in APPN ENs and NNs that support adjacent DLUs by securing services from the DLUS. See also APPN, DLU, and DLUS DLUR Node In APPN networks, an EN or NN that implements the DLUR component. See also DLUR DLUS Dependent LU Server. The DLUS component provides SSCP services to DLUR nodes over an APPN network. See also APPN, DLU, And DLUR DLUS Node In APPN networks, an NN that implements the DLUS pam. See also DLUS DMA Direct memory access. The transfer of data from a peripheral device, such as a hard disk drive, into memory without that data passing through the microprocessor. DMA transfers data into memory at high speeds with no processor overhead DMAC Destination MAC. The MAC address specified in the Destination Address field of a packet. See also MAC address DNA Digital Network Architecture. Network architecture developed by Digital Equipment Corporation. The products that embody DNA including communications protocols are collectively referred to as DECnet. See also DECnet DNIC Data Network Identification Code. Part of an X address. DNICs are divided into two parts: the first specifying the country in which the addressed PSN is located and the second specifying the PSN itself. See also X DNS Domain Name Service DNSIX Department of Defense Intelligence Information System Network Security for Information Exchange. Collection of security requirements for networking defined by the US. Defense Intelligence Agency DoD Department of Defense. Also called dotted notation or four-part dotted notation Dotted Notation See dot address Downlink Station See ground station Download The transfer of a file from a remote computer to a local computer Downsizing The transfer of computing tasks previously performed by main frame or minicomputers to personal computers Downtime A temporary interruption in the usability of a computer system. A work stoppage caused by the temporary lack of usability of acomputer system DQDB Distributed Queue Dual Bus. Data link layer communication protocol, specified in the IEEE standard, designed for use in MANs. DQDB, which permits multiple systems to interconnect using two unidirectional logical buses, is an open standard that is designed for compatibility with carrier transmission standards and is aligned with emerging standards for BISDN. SIP SMDS Interface Protocol is based on DQDB. See also MAN DRAM Dynamic random-access memory. RAM that stores information in capacitors that must be periodically refreshed. Delays can occur because DRAMs are inaccessible to the processor when refreshing their contents. However, DRAMs are less complex and have greater capacity than SRAMs. See also SRAM Drive A data storage device Drop Point on a multipoint channel where a connection to a networked device is made Drop Cable Generally, a cable that connects a network device such as a computer to a physical medium. A type of AUI. See also AUI DS-0 Digital signal level Framing specification used in transmitting digital signals over a single channel at 64-kbps on a T1 facility. Compare with DS-1 and DS DS-1 Digital signal level Framing specification used in transmitting digital signals at Mbps on a T1 facility in the United States or at Mbps on an E1 facility in Europe. Interface circuit used for DS-1 applications with 24 trunks DS-3 Digital signal level Framing specification used for transmitting digital signals at Mbps on a T3 facility. Compare with DS-0 and DS See also E3 and T DSAP Destination service access point. The SAP of the network node designated in the Destination field of a packet. See also SAP service access point DSP Domain specific part. The part of a CLNS address that contains an area identifier, a station identifier, and a selector byte DSPU Downstream physical unit. In SNA, a PU that is located downstream from the host DSPU Concentration See DSPU and PU DSR Data set ready. Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for functions such as signal timing. See also CSU DSX-1 Cross-connection point for DS-1 signals DTE Data Terminal Equipment. Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device for example, a modem and typically uses clocking signals generated by the DCE. CTE includes devices such as computers, protocol translators, and multiplexers. Compare with DCE DTMF Dual tone multifrequency. Use of two simultaneous voice-band tones for dialing such as touch tone DTR Data terminal ready. Convergence algorithm used in Enhanced IGRP that provides loop-free operation at every instant throughout a route computation. Allows routers involved in a topology change to synchronize at the same time, while not involving routers that are unaffected by the change. See also Enhanced IGRP Dual Counter-rotation Ring Network topology in which two signal paths, whose directions are opposite one another, exist in a token-passing network. FDDI and CDDI are based on this concept Dual-homed Station Device attached to multiple FDDI rings to provide redundancy Dual Homing Network topology in which a device is connected to the network by way of two independent access points points of attachment. One access point is the primary connection, and the other is a standby connection that is activated in the event of a failure of the primary connection Dual IS-IS See Integrated IS-IS DVMRP Distance Vector Multicast Routing Protocol. Internetwork gateway protocol, largely based on RIP, that implements a typical dense mode IP multicast scheme. DVMRP uses IGMP to exchange routing datagrams with its neighbors. See also IGMP DXI Data Exchange Interface. Also called adaptive routing E1 Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of Mbps. E1 lines can be leased for private use from common carriers. See also DS E ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of station telephone numbers E3 Wide-area digital transmission scheme, used predominantly in Europe, that carries data at a rate of Mbps. E3 lines can be leased for private use from common carrier. See also DS Email Electronic Mail. A network application that can deliver messagesfrom one computer user to another 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 EARN European Academic Research Network. European network connecting universities and research institutes. EARN merged with RARE to form TERENA. See also RARE and TERENA EBCDIC Extended binary code 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 E Channel Echo channel Kbps ISDN circuit-switching control channel. The E channel was defined in the ITU-TISDN specification, but was dropped in the specification. Compare with B channel, D channel, and H channel Echo In electronic signaling, the reflection of a signal caused by asudden change in the impedance of the carrier A networkcontinuity test where packets are sent to a distant node that isobligated to immediately send the packets back Echo Channel See E channel Echoplex 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 Echo Protocol In the AppleTalk protocol family, a protocol that allows a computer to return test packets. The purpose of Echo Protocol is t testthe delivery conditions to a remote node, including reachability,reliability and round trip time Echo Test A diagnostic test in which packets are sent by one node to another node, which immediately returns them to the original node. Thedata recorded by the echo test includes the success rate of thereturn as well as the time needed to complete the round trip ECMA European Computer Manufacturers Association. Group of European computer vendors who have done substantial OSI standardization work EDI Electronic Document or Data Interchange. The term EDI usuallyconnotes a system where authentication and security methodsguarantee the integrity and origin of the information EDIFACT Electronic Data Interchange for Administration, Commerce, and Transport. Data exchange standard administered by the United Nations to be a multi-industry EDI standard EEPROM Electrically erasable programmable read-only memory. EPROM that can be erased using electrical signals applied to specific pins. See also EPROM EGP Exterior Gateway Protocol. Internet protocol for exchanging routing information between autonomous systems. Documented in RFC Not to be confused with the general term exterior gateway protocol. EGP is an obsolete protocol that has been replaced by BGP. See also BGP EIA Electronic Industries Association. Group that specifies electrical transmission standards. Closely resembles the V. See also Category 1 cabling, Category 2 cabling, Category 3 cabling, Category 4 cabling, Category 5 cabling, and UTP EIGRP See Enhanced IGRP EISA Extended Industry-Standard Architecture bit bus interface used in PCs, PC-based servers, and some Unix workstations and servers. See also ISA ELAN 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 Electromagnetic Interference in the integrity of a signal caused by radiation. An Interference EMI example is the radiation from a fluorescent light, which emits abroad spectrum of electromagnetic radiation, including radiationthat may be harmful to a signal not protected by either shielding oradequate twisting Electronic Mail Widely used network application in which mail messages are transmitted electronically between end users over various types of networks using various network protocols. Often called email EMA Enterprise Management Architecture. Digital Equipment Corporation network management architecture, based on the OSI network management model Email See electronic mail EMI Electromagnetic interference. Interference by electromagnetic signals that can cause reduced data integrity and increased error rates on transmission channels EMIF ESCON Multiple Image Facility. See also ESCON EMP 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 See ELAN Emulation A network activity in which a computer acts as if it is another kindof computer or terminal. An example is when a Macintosh useropens a remote terminal session to a VAX, it may run a programthat emulates a DEC VT240 terminal Emulation Mode Function of an NCP that enables it to perform activities equivalent to those performed by a transmission control unit EN End node. APPN end system that implements the PU 2. ENs are not capable of routing traffic and rely on an adjacent NN for APPN services. See also CP Encapsulation The process of placing one protocol inside of another. Usuallyimplies that the encapsulated protocol was not originally intendedby its designers to be carried by the encapsulating protocol Encapsulation Bridging Carries Ethernet frames from one router to another across disparate media, such as serial and FDDI lines. Contrast with translational bridging Encoder Device that modifies information into the required transmission format Encryption The 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 Enhanced IGRP Enhanced Interior Gateway Routing Protocol. Advanced version of IGRP developed by Cisco. Provides superior convergence properties and operating efficiency, and combines the advantages of link state protocols with those of distance vector protocols. Entities typicallypossess a unique address Entropy A measure of the disorder of a system The thermodynamictendency of a system to reduce its overall energy state by increasing its disorder. Theoretically, an equilibrium is reached where the energy reduction that can be gained by a further increase in entropy is offset by the energy necessary to contain that increase EOT End of Transmission. Generally, a character that signifies the end of a logical group of characters or bits EPROM 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 EEPROM and PROM Equalization Technique used to compensate for communications channel distortions Error checking In data transmission, an action where the integrity of data isverified 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 ES End system. Generally, an end-user device on a network End system. Nonrouting host or node in an OSI network ESCON 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 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 ESD Electrostatic discharge. Discharge of stored static electricity that can damage electronic equipment and impair electrical circuitry, resulting in complete or intermittent failures ESF Extended Superframe Format. Framing type used on T1 circuits that consists of 24 frames of bits each, with the 193rd bit providing timing and other functions. ESF is an enhanced version of SF. See also SF ES-IS End System-to Intermediate System. OSI protocol that defines how end systems hosts announce themselves to intermediate systems routers. See also IS-IS ESnet Energy Sciences Network. Data communications network managed and funded by the U. The DIX version is distinguished bythe reference "Ethernet V. Organization created by the European PTTs and the European Community EC to propose telecommunications standards for Europe EUnet European Internet. European commercial Internet service provider. EUnet is designed to provide electronic mail, news and other Internet services to European markets Event 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 traps Excess Burst See Be Excess Rate 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 EXEC The interactive command process of the Cisco IOS software Expansion The process of running a compressed data set through an algorithm that restores the data set to its original signal. 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 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 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 exterior gateway protocol Any internetwork protocol used to exchange routing information between autonomous systems. Not to be confused with Exterior Gateway Protocol EGPwhich is a particular instance of an exterior gateway protocol 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 Failure Domain Area in which a failure has occurred in a Token Ring, defined by the information contained in a beacon. When a station detects a serious problem with the network such as a cable breakit sends a beacon frame that includes the station reporting the failure, its NAUN, and everything in between. Beaconing in turn intitiates a process called autoreconfiguration. See also autoreconfiguration, beacon, and NAUN Fan-out Unit Device that allows multiple devices on a network to communicate using a single network attachment Fast Ethernet Binary MB network using 4 twisted pairs Fast Switching Cisco feature whereby a route cache is used to expedite packet switching through a router. Contrast with slow switching Fault Management One of five categories of network management defined by ISO for management of OSI networks. Fault management attempts to ensure that network faults are detected and controlled. See also accounting management, configuration management, performance, and security management FCC Federal Communications Commission. The United States government agency that regulates electronic communications and the domestic manufacture and importation of communication equipment FDDI Fiber Data Distributed Interface. A specification ANSI X 3T9. FDDI II provides isochronous transmission for connectionless data circuits and connection-oriented voice and video circuits. Compare with FDDI FDM Frequency-division multiplexing. Technique whereby information from multiple channels can be allocated bandwidth on a single wire based on frequency. Compare with ATDM, statistical multiplexing, and TDM FECN Forward explicit congestion notification. Bit set by a Frame Relay network to inform DTE receiving the frame that congestion was experienced in the path from source to destination. DTE-receiving frames with the FENC bit set can request that higher-level protocols take flow-control action as appropriate. Compare with BECN Female connector Also called "jack". A connector which joins with a male con-nector by providing recesses into which the male connector inserts its contact points or pins FEP Front-end processor. Device or board that provides network interface capabilities for a networked device. In SNA, typically an IBM device Fiber optic A transmission media that uses a light wave for signaling Fiber-optic Cable Physical medium capable of conducting modulated light transmission. Compared with other transmission media, fiber-optic cable is more expensive, but is not susceptible to electromagnetic interference and is capable of higher data rates. Sometimes called optical fiber FID0 Format indicator One of several formats that an SNA TH can use. An FID0 TH is used for communication between an SNA node and a non-SNA node. See also TH FID1 Format indicator One of several formats that an SNA TH can use. An FID1 TH encapsulated messages between two subarea nodes that do not support virtual and explicit routes. See also TH FID2 Format indicator One of several formats that an SNA TH can use. An FID2 TH is used for transferring messages between a subarea node and a PU 2using local addresses. See also TH FID3 Format indicator One of several formats that an SNA TH can use. An FID3 TH is used for transferring messages between a subarea node and a PU 1, using local addresses. See also TH FID4 Format indicator One of several formats that an SNA TH can use. An FID4 TH encapsulates messages between two subarea nodes that are capable of supporting virtual and explicit routes. Generally, if the packet meets the conditions defined in the filter criteria, it under goes further processing. If the packet does not meet the filtercriteria, it is rejected Finder A software application included with Macintosh system softwarethat allows users to perform basic file access and management functions using icons and pull-down menus Finger A collection of software routines used by computers running theIP protocol stack, which allows a user to read public informationabout a user on the same, or a remote machine, often including:full name, telephone number and extension, snail-mail address,time and place of last login, whether user has any pending un-read mail, and witticisms selected pam the user Firewall Router or access server, or several routers or access servers, designated as a buffer between any connected public networks and a private network. For example, the ZIP GetNetInfo Reply includes a 1-bitflag that indicates whether the zone name specified either is or isnot a valid home zone name for the node that requested the information Flag Byte In LocalTalk signaling, the bit pattern " ", which signalsthe beginning and ending of a LLAP frame. The Flag Bytes preceding the packets establish the synchronization of the framesimilar to the function of an Ethernet preamble Flapping Routing problem where an advertised route between two nodes alternates flaps back and forth between two paths due to a network problem that causes intermittent interface failures Flash memory Technology developed by Intel and licensed to other semiconductor companies. Flash memory is nonvolatile storage that can be electrically erased and reprogrammed. Allows software images to be stored, booted, and rewritten as necessary Flash Update Routing update sent synchronously in response to a change in the network topology. Compare with routing update Flooding Traffic-passing technique used by switches and bridges in which traffic received on an interface is sent out all of the interfaces of that device except the interface on which the information was originally received Flow Stream of data traveling between two endpoints across a network for example, from one LAN station to another. Multiple flows can be transmitted on a single circuit Flow Control Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed. In IBM networks, this technique is called pacing FM Frequency Modulation. In data transmission, a system of signaling in which the data is encoded by varying the frequency of the signal FNC Federal Networking Council. Group responsible for assessing and coordinating U. Examples include the format of disk, file or packet Format Indicator 0 See FID Format Indicator 1 See FID Format Indicator 2 See FID Format Indicator 3 See FID Format Indicator 4 See FID Forward Channel Communications path carrying information from the call initiator to the called party Forward Delay Interval Amount of time an interface spends listening for topology change information after that interface has been activated for bridging and before forwarding actually begins Forwarding Process of sending a frame toward its ultimate destination by way of an internetworking device Fourier Transform Technique used to evaluate the importance of various frequency cycles in a time series pattern Four-part Dotted Notation See dot address FQDN Fully Qualified Domain Name. Any network device that provides a connection between a LAN and a Frame Relay WAN Fragment Piece of a larger packet that has been broken down to smaller units Fragmentation Process of breaking a packet into smaller units when transmitting over a network medium that cannot support a packet of the original size. See also reassembly Frame In data networks, the information packet and all of the precedingand succeeding signals necessary flag bytes, preambles, framechecks, abort sequences, etc. Frame relay is more efficient than X. See also X Frame Relay Bridging Bridging technique, described in RFCthat uses the same spanning-tree algorithm as other bridging functions, but allows packets to be encapsulated for transmission across a Frame Relay network Frame Switch See LAN switch Free-trade Zone Part of an AppleTalk internetwork that is accessible by two other parts of the internetwork that are unable to directly access one another Frequency A measure of the rate of change of a signal In a periodic signal, the reciprocal of the time necessary to complete oneperiod Front End Node or software program that requests services of a back end. See also back end, client, and server FST Fast Sequenced Transport. Connectionless, sequenced transport protocol that runs on top of the IP protocol. SRB traffic is encapsulated inside of IP datagrams and is passed over an FST connection between two network devices such as routers. Speeds up data delivery, reduces overhead, and improves the response time of SRB traffic FTAM The OSI standard for File Transfer, Access and Management FTP File Transfer Protocol. Lowest-common-denominator protocolfor the point-to-point transfer of text and binary files between IP connected hosts Full-duplex A communication system between two entities in which eitherentity can transmit simultaneously Full Mesh Term describing a network in which devices are organized in a mesh topology, with each network node having either a physical circuit or a virtual circuit connecting it to every other network node. A full mesh provides a great deal of redundancy, but because it can be prohibitively expensive to implement, it is usually reserved for network backbones. See also mesh and partial mesh Fuzzball Digital Equipment Corporation LSI-11 computer system running IP gateway software. The NSFnet used these systems as backbone packet switches G G ITU-T electrical and mechanical specifications for connections between telephone company equipment and DTE using BNC connectors and operating at E1 data rates G ITU-T framing standard that defines the mapping of ATM cells into the physical medium Gateway A device that performs a protocol translation at the SessionLayer or higher Archaic. Cisco protocol that allows hosts to dynamically detect the arrival of new routers as well as determine when a router goes down. See also UDP Generic Routing Encapsulation See GRE Get In SNMP, a command given by the Console to retrieve a single data structure from a MIB Get Nearest Server See GNS GGP Gateway-to-Gateway Protocol. MILNET protocol specifying how core routers gateways should exchange reachability and routing information. GGP uses a distributed shortest-path algorithm GHz Gigahertz Giga A prefix denoting a billion GNS Get Nearest Server. Request packet sent by a client on an IPX network to locate the nearest active server of a particular type. An IPX network client issues a GNS request to solicit either a direct response from a connected server or a response from a router that tells it where on the internetwork the service can be located. GNS is part of the IPX SAP. See also IPX and SAP Service Advertisement Protocol GOSIP Government OSI Profile. US Government procurement standard that specified interoperability standards for computing equipmentand software purchased Grade Also Level or Category. In the specification of wiring for data networks, a standard designation used to describe the electricalquality of the wiring with regard to its suitability to carry high-speed signals Grade of Service Measure of telephone service quality based on the probability that a call pam encounter a busy signal during the busier hours of the day GRE Generic Routing Encapsulation. Tunneling protocol developed by Cisco that can encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to Cisco routers at remote points over an IP internetwork. By connecting multiprotocol subnetworks in a single-protocol backbone environment, IP tunneling using GRE allows network expansion across a single-protocol backbone environment Ground An electrical conductor that is neither negatively or positively charged Ground Station Collection of communications equipment designed to receive signals from and usually transmit signals to satellites. Also called a downlink station Group Address See multicast address Group Delay See distortion delay Guard Band Unused frequency band between two communications channels that provides separation of the channels to prevent mutual interference GUI Graphical User Interface. User environment that uses pictorial as well as textual representations of the input and output of applications and the hierarchical or other data structure in which information is stored. Conventions such as buttons, icons, and windows are typical, signal many actions are performed using a pointing device such as a mouse Hacker An expert computer programmer A knowledgeable but disruptive computer user Half Duplex Capability for data transmission in only one direction at a time between a sending station and a receiving station. Compare with full duplex and simplex Handshake Sequence of messages exchanged between two or more network devices to ensure transmission synchronization Hardware Address An address, fixed at the time of manufacturing, that identifies a network adapter such as an Ethernet card HBD3 Line code type used on E1 circuits H Channel High-speed channel. Full-duplex ISDN primary rate channel operating at Kbps. Compare with B channel, D channel, and E channel HDLC High-level Data Link Control. An ISO standard for encapsulation of data on synchronous links Headend The end point of a broadband network. All stations transmit toward the headend; the headend then transmits toward the destination station Header In a network packet or frame, a section of data that describes the data that immediately follows Heap The RAM memory pam by system software and system extensions to hold frequently used instructions and data not contained in ROM or firmware Heartbeat See SQE HELLO Interior routing protocol used principally by NSF net nodes. HELLO allows particular packet switches to discover minimal delay routes. Not to be confused with the Hello protocol Hello Packet Multicast packet that is used by routers for neighbor discovery and recovery. Hello packets also indicate that a client is still operating and network-ready Hello Protocol Protocol used by OSPF systems for establishing and maintaining neighbor relationships. Not to be confused with HELLO Helper Address Address configured on an interface to which broadcasts received on that interface will be sent HEPnet High-Energy Physics Network. Research network that originated in the United States, but that has spread to most places involved in high-energy physics. Well-known sites include Argonne National Laboratory, Brookhaven National Laboratory, and the Stanford Linear Accelerator Center SLAC Hertz HZ A unit of measure of the frequency of cyclic wave form, equal to one cycle or period per second Heterogeneous Network Network consisting of dissimilar devices that run dissimilar protocols and in many cases support dissimilar functions or applications Hexadecimal A numerical system with a base of 16 that is useful for expressing digital data. One hexadecimal digit represents for bits HFS Hierarchical File System Hierarchical Routing Routing based on a hierarchical addressing system. For example, IP routing algorithms use IP addresses, which contain network numbers, subnet numbers, and pam numbers Hint In dynamic addressing, an address that a node will test for uniqueness first. The hint is either the last successful address the node used previously the Macintosh keeps such a hint in PRAM or a particular address that is specific to a particular model of device the GatorBox always tries first or LocalTalk networks HIPPI High-Performance Parallel Interface. High-performance interface standard defined by ANSI. HIPPI is typically used to connect supercomputers to peripherals and other devices Holddown State into which a route is placed so that routers will neither advertise the route nor accept advertisements about the route for a specific length of time the holddown period. Holddown is used to flush bad information about a route from all routers in the network. A route is typically placed in holddown when a link in that route fails Homologation Conformity of a product or specification to international standards, such as ITU-t, CSA, TUV, UL, or VCCI. Enables portability across company and international boundaries Hop In routed networks, the passage of a packet through a router on the way to its destination Hop Count In AppleTalk packets, a 4-bit counter in the DDP header that is incremented each time a packet passes through a router on the way to its destination Hop Distance A unit of measure used to express the number or routers that a packet must pass through its way to its destination Host In terminal emulation, the remote computer that is being controlled by the terminal emulation software Host Address See host number Host Node SNA subarea node that contains an SSCP Host Number Part of an IP address that designates which node on the subnetwork is being addressed. Also called a host address Hot Standby Router Protocol See HSRP HPCC High Performance Computing and Communications. The HPCC is designed to ensure US. The five components of the HPCC are ASTA, BRHR, HPCS, IITA, and NREN HPCS High Performance Computing Systems. Component of the HPCC program designed to ensure US. See also HPCC HPR High Performance Routing. Second-generation routing algorithm for APPN. HPR provides a connectionless layer with nondisruptive routing of sessions around link failures, and a connection-oriented layer with end-to-end flow control, error control, and sequencing. See also APPN HSRP Hot Standby Router Protocol. Provides high network availability and transparent network topology changes. HSRP creates a Hot Standby router group with a lead router that services all packets sent to the Hot Standby address. The lead router is monitored by other routers in the group, and if it fails, one of the standby routers inherits the lead position and the Hot Standby group address HSSI High-Speed Serial Interface. Network standard for high-speed up to 52 Mbps serial connections over WAN links Signal Hypertext markup language. Simple hypertext document formatting language that uses tags to indicate how a given part of a document should be interpreted by a viewing application, such as a WWW browser. See also hypertext and WWW browser Hub Generally, a term used to describe a device that serves as the center of a star-topology network Hardware of software devices that contains multiple independent but connected modules of network and internetwork equipment. Hubs can be active where they repeat signals sent through them or passive where they do not repeat, but merely split, signals sent through them In Ethernet and IEEEan Ethernet multiport repeater, sometimes referred to as a concentrator Hybrid Network Internetwork made up of more than one type of network technology, including LANs and WANs Hypertext Electronically-stored text that allows direct access to other texts by way of encoded links. Hypertext documents can be created using HTML, and often integrate images, sound, and other media that are commonly viewed using a WWW browser. Board of internetwork researchers who discuss issues pertinent to Internet architecture. Responsible for appointing a variety of Internet-related groups such as the IANA, IESG, and IRSG. The IAB is appointed by the trustees of the ISOC. See also IANA, IESG, IRSG, and ISOC IANA Internet Assigned Numbers Authority. Organization operated under the auspices of the ISOC as a part of the IAB. IANA delegates authority for IP address-space allocation and domain-name assignment to the NIC and other organizations. See also IAB, ISOC, and NIC ICD International Code Designator. One of two ATM address formats developed by the ATM forum for use by private networks. Adapted from the subnetwork model of addressing in which the ATM layer is responsible for mapping network layer addresses to ATM addresses. See also DCC ICMP Internet Control Message Protocol. Network layer Internet protocol that reports errors and provides other information relevant to IP packet processing. Documented in RFC ICMP Router Discovery Protocol See IRDP Icon A pictographic symbol used to represent a computer concept or operation IDI Initial domain identifier. In OSI, the portion of the NSAP that specifies the domain IDN International Data Number. See X IDP Initial domain part. The part of a CLNS address that contains an authority and format identifier and a domain identifier IDPR Interdomain Policy Routing. Interdomain routing protocol that dynamically exchanges policies between autonomous systems. IDPR encapsulates interautonomous system traffic and routes it according to the policies of each autonomous system along the path. IDPR is currently an IETF proposal. See also policy routing IDRP IS-IS Interdomain Routing Protocol. OSI protocol that specifies how routers communicate with routers in different domains IEC International Electrotechnical Commission. Industry group that writes and distributes standards for electrical products and components IEEE The Institute or Electrical and Electronic Engineers, a non-profit organization that, among many other activities, endeavors to coordinate, synthesize and promote data networking standards IEEE IEEE specification that describes an algorithm that prevents bridging loops by creating a spanning tree. The algorithm was invented by Digital Equipment Corporation. The Digital algorithm and the IEEE algorithm are not exactly the same, nor are they compatible. See also spanning tree, spanning-tree algorithm, and Spanning-Tree Protocol IEEE IEEE LAN standard that specifies the physical layer and the MAC sublayer of the data link layer. IEEE uses the demand priority media-access scheme at Mbps over a variety of physical media. See also 100VG-AnyLAN IEEE The committee of the IEEE charged with the responsibility of coordinating standards at the Data Link Layer. The committee also oversees the work of many sub-committees that govern individual Data Link standards such as the standard IEEE IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. Extensions to the IEEE standard specify implementations for Fast Ethernet. Physical variations of the original IEEE specifications include 10Base2, 10Base5, 10BaseF, 10BaseT, and 10Broad Physical variations for fast ethernet include 100BaseT, 100BaseT4, and 100BaseX IEEE IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE uses token-passing access over a bus topology and is based on the token bus LAN architecture. See also token bus IEEE IEEE LAN protocol that specifies an implementation of the physical layer and MAC sublayer of the data link layer. IEEE uses token passing access at 4 or 16 Mbps over STP cabling and is similar to IBM Token Ring. See also Token Ring IEEE IEEE MAN specification based on DQDB technology. IEEE supports data rates of to Mbps. See also DQDB IESG Internet Engineering Steering Group. Organization, appointed by the IAB, that manages the operation of the IETF. See also IAB and IETF IETF Internet Engineering Task Force. Task force consisting of over 80 working groups responsible for developing Internet standards. The IETF operates under the auspices of ISOC. See also ISOC IGP Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include IGRP, OSPF, and RIP. See also IGRP, OSPF, and RIP IGMP Internet Group Management Protocol. Used by IP hosts to report their multicast group memberships to an adjacent multicast router IGRP Interior Gateway Routing Protocol. IGP developed by Cisco to address the problems associated with routing in large, heterogeneous networks. Compare with Enhanced IGRP. See also IGP, OSPF, and RIP IIH IS-IS Hello. Message sent by all IS-IS systems to maintain adjacencies. See also IS-IS IITA Information Infrastructure Technology and Applications. Component of the HPCC program intended to ensure U. See also HPCC ILMI Interim Local Management Interface. Specification developed by the ATM Forum for incorporating network-management capabilities in the ATM UNI IMP Interface message processor. Old name for ARPANET packet switches. An IMP is now referred to as a PSN packet-switch node. See also PSN packet-switch node Impedance A measure of the opposition to the flow of an alternating signal by its media Implementation The physical manifestation of a network standard or design In-band signaling Transmission within a frequency range normally used for information transmission. Compare with out-of-band signaling Infrared A portion of electromagnetic spectrum situated between visible light and microwaves A means of short distance wireless networking that depends on an unobstructed line of binary path INIT Archaic. A Macintosh System Extension Initialization The entry of a set of process parameters performed by a human or automatically loaded from a file that are necessary to begin a software process INOC Internet Network Operations Center. BBN group that in the early days of the Internet monitored and controlled the Internet core gateways routers. The insured burst is specified in bytes or cells. Compare with maximum burst. See also insured rate Insured Rate The long-term data throughput, in bits or cells per second, that an ATM network commits to support under normal network conditions. The insured rate is percent allocated; the entire amount is deducted from the total trunk bandwidth along the path of the circuit. Compare with excess rate and maximum rate. See also insured burst Insured Traffic Traffic within the insured rate specified for the PVC. This traffic should not be dropped by the network under normal network conditions. See also CLP and insured rate Integrated IS-IS Routing protocol based on the OSI routing protocol IS-IS but with support for IP and other protocols. Integrated IS-IS implementations send only one set of routing updates, making it more efficient than two separate implementations. Formerly referred to as Dual IS-IS. Compare IS-IS Integrated Service Digital Network See ISDN Integrity In networking, a desirable condition where the information received is exactly equal to the information sent Intelligence The ability of a system to use pam information to respond appropriately to specific events Interarea Routing Term used to describe routing between two or more logical areas. Sometimes called an internet, which is not to be confused with the Internet Internetworking General term used to refer to the industry that has arisen around the problem of connecting networks together. The term can refer to products, procedures, and technologies Internetwork Packet Exchange See IPX Interoperability Ability of computing equipment manufactured by different vendors to communicate with one another successfully over the network Inter-Switching System Interface See ISSI Intra-area Routing Term used to describe routing within a logical area. Compare with interarea routing Inverse ARP Inverse Address Resolution Protocol. Method of building dynamic routes in a network. IP provides features for addressing, type-of-service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. An IP address belongs to one of five classes A, B, C, D, or E and is written as 4 octets separated with periods dotted decimal format. Each address consists of a network number, an optional subnet work number, and a host number. The network and subnetwork numbers together are used for routing, while the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address. Also called an Internet address. See also IP and subnet mask IP Multicast Routing technique that allows IP traffic to be propagated from one source to a number of destinations or from many sources to many destinations. Rather than sending one packet to each destination, one packet is sent to a multicast group identified by a single IP destination group address IP Security Option See IPSO IPSO IP Security Option. A protocol family that is proprietary to the Novell Netware system IPXWAN Protocol that negotiates end-to-end options for new links. When a link comes up, the first IPX packets sent across are IPXWAN packets negotiating the options for the link. When the IPXWAN options have been successfully determined, normal IPX transmission begins. Defined by RFC IRDP ICMP Router Discover Protocol. Enables a host to determine the address of a router that it can use as a default gateway. Similar to ES-IS, but used with IP. See also ES-IS IRN Intermediate routing node. In SNA, a subarea node with intermediate routing capability IRSG Internet Research Steering Group. Group that is part of the IAB and oversees the activities of the IRTF. See also IAB and IRTF IRTF Internet Research Task Force. Community of network experts that consider Internet-related research topics. The IRTF is governed by the IRSG and is considered a subsidiary of the IAB. See also IAB and IRSG IS Intermediate system. Routing node in an OSI network ISA Industry-Standard Architecture bit bus used for Intel-based personal computers. See also EISA Isarithmic Flow Control Flow control technique in which permits travel through the network. Signal of these permits grants the right to transmit. Isarithmic flow control is not commonly implemented ISDN Integrated Services Digital Network. Communication protocol, offered by telephone companies, that permits telephone networks to carry data, voice, and other source traffic. See also BISDN, BRI, N-ISDN, and PRI IS-IS Intermediate System to Intermediate System. A dynamic routing protocol for IP ISO International organization that is responsible for a wide range of standards, including those relevant to networking. ISO developed the OSI reference model, a popular networking reference model ISO HDLC procedures developed by ISO. ISO specifies the HDLC frame structure for use in synchronous environments. ISO specifies proposed modifications to allow the use of HDLC in asynchronous environments as well ISO Set of international quality-management standards defined by ISO. The standards, which are not specific to any country, industry, or product, allow companies to demonstrate that they have specific processes in place to maintain an efficient quality system ISOC Internet Society. International nonprofit organization, founded inthat coordinates the evolution and use of the Internet. In addition, ISOC delegates authority to other groups related to the Internet, such as the IAB. ISOC is headquartered in Reston, Virginia, U. See also IAB Isochronous Transmission Asynchronous transmission over a synchronous data link. Isochronous signals require a constant bit rate for reliable transport. Compare with asynchronous transmission, plesiochronous transmission, and synchronous transmission ISODE ISO development environment. Large set of libraries and utilities used to develop upper-layer OSI protocols and applications ISO Development Environment See ISODE ISR Intermediate Session Routing. Initial routing algorithm used in APPN. ISR provides node-to-node connection-oriented routing. Network outages cause sessions to fail because ISR cannot provide nondisruptive rerouting around a failure. ISR has been replaced by HPR. See also APPN ISSI Inter-Switching System Pam. Standard interface between SMDS switches ITU-T International Telecommunication Union Telecommunication Standardization Sector. International body that develops worldwide standards for telecommunications technologies. The ITU-T carries out the functions of the former CCITT. See also CCITT Jabber Error condition in which a network device continually transmits random, meaningless data onto the network In IEEEa data packet whose length exceeds that prescribed in the standard Jack The female connector Jacket The protective outer covering of a computer or network cable JANET Joint Academic Network. Different circuits are signal by attaching the connector to different pins JUNET Japan UNIX Network. Nationwide, noncommercial network in Japan, designed to promote communication between Japanese and signal researchers JvNCnet John von Neumann Computer Network. Regional network, owned and operated by Global Enterprise Services, Inc. Technology that allows an ATM network to function as a LAN backbone. The ATM network must provide multicast and broadcast support, address mapping MAC-to-ATMSVC management, and a usable packet format. LANE also defines Ethernet and Token Ring ELANs. See also ELAN LAN Emulation See LANE LAN Emulation Client See LEC LAN Manager Distributed NOS, developed by Microsoft, that supports a variety of protocols and platforms LAN Server A general term used to describe a device that manages and allows the use of more than one kind of resource such as storage or file services, print services, communication services, data base services, etc LAN Switch High-speed switch that forwards packets between data-link segments. Most LAN switches forward traffic based on MAC addresses. This variety of LAN switch is sometimes called a frame switch. LAN switches are often categorized according to the method they use to forward traffic: cut-through packet switching or store-and-forward packet switching. Multilayer switches are an intelligent subset of LAN switches. Compare with multilayer switch. See also cut-through packet switching and store and forward packet switching LAP Link Access Protocol. Any protocol of the Data Link Layer, such as EtherTalk LAPB Link Access Procedure, Balanced. Data link layer protocol in the X. LAPB is a bit-oriented protocol derived from HDLC. See also HDLC and X LAPD Link Access Procedure on the D channel. ISDN data link layer protocol for the D channel. LAPD was derived from the LAPB protocol and is designed primarily to satisfy the signaling requirements of ISDN basic access. Defined by ITU-T Recommendations Q and Q LAPM Link Access Procedure for Modems. ARQ used by modems implementing the V. See also ARQ and V Laser Light amplification by simulated emission of radiation. Analog transmission device in which a suitable active material is excited by an external stimulus to produce a narrow beam of coherent light that can be modulated into pulses to carry data. Networks based on laser technology are sometimes run over SONET LaserWriter Any of a group of laser printers that uses PostScript as an imaging language and can communicate using AppleTalk protocols LAT Local Area Transport. See VCN LCN Logical channel number. See VCN Leaf Internetwork In a star topology, an internetwork whose sole access to other internetworks in the star is through a core router Learning Bridge Bridge that performs MAC address learning to reduce traffic on the network. Pam bridges manage a database of MAC addresses and the interfaces associated with each address. See also MAC address learning Leased Line Transmission line reserved by a communications carrier for the private use of a customer. A leased line is a type of dedicated line. See also dedicated line LEC LAN Emulation Client. Entity in an end system that performs data forwarding, address resolution, and other control functions for a single ES within a single ELAN. A LEC also provides a standard LAN service interface to any higher-layer entity that interfaces to the LEC. Each LEC is identified by a unique ATM address, and is associated with one or more MAC addresses reachable through that ATM address. See also ELAN and LES LECS LAN Emulation Configuration Server. Entity that assigns individual LANE clients to particular ELANs by directing them to the LES that corresponds to the ELAN. There is logically one LECS per administrative domain, and this serves all ELANs within that domain. See also ELAN LED Light emitting diode. Semiconductor device that emits light produced by converting electrical energy. Status lights on hardware devices are typically LEDs LEN node Low-entry networking node. In SNA, a PU the supports LU protocols, but whose CP cannot communicate with other nodes. Because there is no CP-to-CP session between a LEN node binary its NN, the LEN node must have a statically defined image of the APPN network LES LAN Emulation Server. Entity that implements the control function for a particular ELAN. There is only one logical LES per ELAN, and it is identified by a unique ATM address. See also ELAN Level 1 Router Device that routes traffic within a single DECnet or OSI area Level 2 Router Device that routes traffic between DECnet or OSI areas. All Level 2 routers must form a contiguous network Light Emitting Diode See LED Limited Resource Resource Link defined by a device operator to remain active only when being used Limited-route Explorer Packet See spanning explorer packet Line In SNA, a connection to the network See link Line Code Type One of a number of coding schemes used on serial lines to maintain data integrity and reliability. The line code type used is determined by the carrier service provider. See also AMI and HBD Line Conditioning Use of equipment on leased voice-grade channels to improve analog characteristics, thereby allowing higher transmission rates Line Driver Inexpensive amplifier and signal converter that conditions digital signals to ensure reliable transmissions over extended distances Line of Sight Characteristic of certain transmission systems, such as laser, microwave, and infrared systems, in which no obstructions in a direct path between transmitter and receiver can exist Line Printer Daemon See LPD Line Turnaround Time required to change data transmission direction on a telephone line Link Network communications channel consisting of a circuit or transmission path and all related equipment between a sender and a receiver. Most often used to refer to a WAN connection. Sometimes referred to as a line or a transmission link Link Layer See data link layer Link-Layer Address See MAC address Link-state Advertisement See LSA Link State Routing A routing protocol that takes link loading and bandwidth when selecting between alternate routes. Example: OSPF Link State Routing Algorithm Algorithm Routing algorithm in which each router broadcasts or multicasts information regarding the cost of reaching each of its neighbors to all nodes in the internetwork. Link state algorithms create a consistent view of the network and are therefore not prone to routing loops, but they achieve this at the cost of relatively greater computational difficulty and more widespread traffic compared with distance vector routing algorithms. Compare with distance vector routing algorithm. Compare with big-endian LLC Logical Link Control LLC2 Logical Link Control, type2. Connection-oriented OSI LLC-sublayer protocol. See also LLC LMI Local Management Interface. Set of enhancements to the basic Frame Relay specification. Monitors LAN devices in UNIX environments LNM LAN Network Manager. SRB and Token Ring management package provided by IBM. Typically running on a PC, it monitors SRB and Token Ring devices and can pass alerts up in NetView Load Balancing In routing, the pam of a router to distribute traffic over all its network ports that are the same distance from the destination address. Good load-balancing algorithms use both line speed and reliability information. Load balancing increases the utilization of network segments, thus increasing effective network bandwidth Local Access and Transport Area See LATA Local Acknowledgment Method whereby an intermediate network node, such as a router, responds to acknowledgments for a remote end host. Use of local acknowledgments reduces network overhead and, therefore, the risk of time-outs. Also known as local termination Local-area Network See LAN Local-area Transport See LAT Local Bridge Bridge that directly interconnects networks in the same geographic area Local Exchange Carrier See LEC Local Explorer Packet Generated by an end system in an SRB network to find a host connected to the local ring. If the local explorer packet fails to find a local host, the end system produces either a spanning explorer packet or an all-routes explorer packet. Defined in the IEEE standard. See also IEEE Logical Address See network address Logical Channel Nondedicated, packet-switched communications path between two or more network nodes. The purpose of this test is typically to establish that the adapter is connected to a network that is functional enough to support a data transmission Loss The aggregate attenuation of a signal due to interaction with its environment LSP Link State Packet. Protocol used to send print jobs between UNIX systems LSA Link-state Advertisement. Broadcast packet used by link-state protocols that contains information about neighbors and path costs. LSAs are used by the receiving routers to maintain their routing tables. Sometimes called a link-state packet LSP LSP Link State Packet. The method whereby a computing device takes control of the transmission media for the purpose of sending an information packet Mac address Standardized data link layer address that is required for every port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, a MAC-layer address, or a physical address MAC address learning Service that characterizes a learning bridge, in which the source MAC address of each received packet is stored so that future packets destined for that address can be forwarded only to the bridge interface on which that address is located. Packets destined for unrecognized addresses are forwarded out every bridge interface. This scheme helps minimize traffic on the attached LANs. MAC address learning is defined in the IEEE standard MacIP Network layer protocol that encapsulates IP packets in DDS or transmission over AppleTalk. MacIP also provides proxy ARP services Magnetic field The area surrounding an electrically charged body in which an electromagnetic force can be detected Mainframe An expensive, general purpose computer with the ability to be used by many users simultaneously Male connector A connector whose points of electrical contact are exposed MAN metropolitan-area network. Network that spans a metropolitan area. Generally, a MAN spans a larger geographic area than a LAN, but a smaller geographic area that a WAN Managed Object In network management, a network device that can be managed by a network management protocol Management Services SNA functions distributed among network components to manage and control an SNA network Manchester encoding Digital coding scheme, used by IEEE and Ethernet, in which a mid-bit-time transition is used for clocking, and a 1 is denoted by a high level during the first half of the bit time MAP Manufacturing Automation Protocol. Network architecture created by General Motors to satisfy the specific needs of the factory floor. MAP specifies a token-passing LAN similar to IEEE MAPI Microsoft Application Programming Interface. A programming library for Windows developers that provides messaging services to their applications Mask See address mask and subnet mask MAU Media Access Unit. The component of a network adapter that directly attaches to the Transmission media Maximum Burst Specifies the largest burst of data above the insured rate that will be allowed temporarily on an ATM PVC but will not be dropped at the edge by the traffic policing function, even if it exceeds the maximum rate. This amount of traffic will be allowed only temporarily; on average, the traffic source needs to be within the maximum rate. Specified in bytes or cells Maximum Rate Maximum total data throughput allowed on a given virtual circuit, equal to the sum of the insured and uninsured traffic from the traffic source. The uninsured data might be dropped if the network becomes congested. The maximum rate, which cannot exceed the media rate, represents the highest data throughput the virtual circuit will ever deliver, measured in bits or cells per second MBONE Multicast backbone. The multicast backbone of the Internet. MBone is a virtual multicast network composed of multicast LANs and the point-to-point tunnels that interconnect them MBPS A unit of measure used to describe the rate of data transmission equal to one millions bits per second MByte A unit of measure used to describe an amount of information equal to 1,048, bytes MCA Micro channel architecture. Bus interface commonly used in PCs and some UNIX workstations and servers MCI Multiport Communications Interface. The MCI processes packets rapidly, without the interframe delays typical of other Ethernet interfaces MCR minimum cell rate. MCR is defined only for ABR transmissions, and specifies the minimum value for the ACR MD5 Message Digest Algorithm used for message authentication in SNMP v. MD5 verifies the integrity of the communication, authenticates the origin, and checks for timelines Media The environment in which the transmission signal is carried Media Rate Maximum traffic throughput for a particular media type Memory In computing, a system where data is stored for direct, highspeed access by a microprocessor Memory Allocation The amount of memory, usually RAM, that an process reserves for itself Mesh Network topology in which devices are organized in a manageable, segmented manner with many, often redundant, interconnections strategically placed between network nodes Message Application layer Layer 7 logical grouping of information, often composed of a number of lower-layer logical groupings such as packets. The terms datagram, frame, packet, and segment are also used to describe logical information groupings at various layers of the OSI reference model Message Switching Switching technique involving transmission of messages from node to node through a network. The message is stored at each node until such time as a forwarding path is available Message Unit Unit of data processed by any network layer Metalanguage A language that represents another language Metasignaling Process running at the ATM layer that manages signaling types and virtual circuits MHS Message Handling Service. A synonym of X store and forward messaging Message Handling System. A Novell protocol for mail handling MIB Management Information Base. In SNMP, a specification of the data objects and data structures that the Agent is responsible for knowing and reporting to the Console on demand MIC Media interface connector. FDDI de facto standard connector Micro A prefix that denotes a one millionth part of a unit of measure, such as a microsecond or microampere A prefix that denotes something small A slang term for any personal computer Microcode Translation layer between machine instructions and the elementary operations of a computer. Microcode is stored in ROM and allows the addition of new machine instructions without requiring that they be designed into electronic circuits when new instructions are needed Microsegmentation Division of a network into smaller segments, usually with the intention of increasing aggregate bandwidth to network devices Microwave Any electromagnetic radiation with a wavelength between 1 millimeter and 1 meter A point-to-point data transmission system employing electromagnetic radiation using a carrier frequency in the microwave region MIDI Musical Instrument Digital Interface Midsplit Broadband cable system in which the available frequencies are split into two groups: one for transmission and one for reception Milli A prefix denoting a one thousandth part of a unit of measure, such as a millisecond or millimeter MILNET Signal Network. Unclassified portion of the DDN. Operated and maintained by the DISA Minicomputer Archaic. A multi-user computer capable of supporting simultaneous users Mips Millions of instructions per second. Number of instructions executed by a processor per second MIS Management Information System. Used to describe the set of computing resources that hold and allow access to the information owned by an organization Mode One particular method or way of accomplishing a goal In fiber optic transmission, a particular path between a light source and a receiver In statistics, the result with the highest pam within the sample group Modem A device that can covert data signals between analog and digital signaling systems Modem eliminator Device allowing connection of two DTE devices without modems Modulation Process by which the characteristics of electrical signals are transformed to represent information. Types of modulation include AM, FM, and PAM Modulator-demodulator See Modem MOP Maintenance Operation Protocol. Digital Equipment Corporation protocol that provides a way to perform primitive maintenance operations on DECnet systems Mosaic Public-domain WWW browser, developed at the National Center for Supercomputing Applications NCSA MOSPF Multicast OSPF. Intradomain multicast routing protocol used in OSPF networks. Extensions are applied to the base OSPF unicast protocol to support IP multicast routing MOV Metal Oxide Varister. A device that acts as a surge suppresser by forcing transient high voltages to ground MQI Message Queueing Interface. International standard APO that provides functionality similar to that of the RPC interface. In contrast to RPC, MQI is implemented strictly at the application layer MSAU Multistation access unit. Wiring concentrator to which all end stations in a Token Ring network connect. The MSAU provides an interface between these devices and the Token Ring interface MSL Maximum Segment Lifetime MSS Maximum Segment Size MTA Message Transfer Agent. A specification in a data link protocol that defines the maximum number of bytes that can be carried in any one packet on that link Mu-law North American companding standard used in conversion between analog and digital signals in PCM systems Multiaccess Network Network that allows multiple devices to connect and communicate simultaneously Multicast Single packets copied by the network and sent to a specific subset of network addresses. These addresses are specified in the destination address field Multicast Group Dynamically determined group of IP hosts identified by a single IP multicast address Multicast router Router used to send IGMP query messages on their attached local networks. Host members of a multicast group respond to a query by sending IGMP reports noting the multicast groups to which they belong. The multicast router takes responsibility for forwarding multicast datagrams from one multicast group to all other networks that have members in the group Multicast Server Establishes a one-to-many binary to each device in a VLAN, thus establishing a broadcast domain for each VLAN segment. The multicast server forwards incoming broadcasts only to the multicast address that maps to the broadcast address Multidrop Line Communications line having multiple cable access points. Sometimes called a multipoint line Multihomed Host Host attached to multiple physical network segments in an OSI CLNS network Multihoming Addressing scheme in IS-IS routing that supports assignment of multiple area addresses Multilayer switch Switch that filters and forwards packets based on MAC addresses and network addresses. A subset of LAN switch Multimode Fiber Optical fiber supporting propagation of multiple frequencies of light Multiple Domain Network SNA network with multiple SSCPs Multiplexing Signal that allows multiple logical signals to be transmitted simultaneously across a single physical channel Multi-user A term used to describe a computing process that can handle the requirements of several users simultaneously Multitasking A descriptive term for a computing device whose operating system can handle several tasks concurrently. In monoprocessors, each active task is given short periods of time to use the CPU in a rotational fashion Multivendor network Network using equipment from more than one vendor MVS Multiple Virtual Storage. One algorithm reduces the sending window; the other limits small datagrams NAK Negative acknowledgment. Response sent from a receiving device to a sending device indicating that the information received contained errors Name Caching Method by which remotely discovered host names are stored by a router for use in future packet-forwarding decisions to allow quick access Name Server Server connected to a network that resolves network names into network addresses Name Service In AppleTalk, a computing process that has used Name Binding Protocol to register a process so that it may be located using a network resource management like the Chooser Nano A prefix that denotes a 1 billionth portion of a unit of measure, as in nanosecond or nanometer NAP Network access point. Location for interconnection of internet service providers in the United States for the exchange of packets Native Something is a standard component of a computer system, such as a native file system or a native protocol NAU Network addressable unit. SNA term for an addressable entity. Examples include LUs, PUs, and SSCPs. NAUs generally provide upper-level network services NAUN Nearest active upstream neighbor. In Token Ring or IEEE networks, the closest upstream network device from any given device that is still active NBMA Nonbroadcast multiaccess. Term describing a multiaccess network that either does not support broadcasting such as X or in which broadcasting is not feasible for example, an SMDS broadcast group or an extended Ethernet that is too large NBP Name Binding Protocol. The AppleTalk protocol that associates the name, type and zone of a process with its Internet Socket Address NCP Network Control Protocol NEARNET Regional network in New England United States that links Boston University, Harvard University, and MIT Neighboring Routers In OSPF, two routers that have interfaces to a common network. On multiaccess networks, neighbors are dynamically discovered by the OSPF Hello signal NET Network entity title. API used by applications on an IBM LAN to request services from lower-level network processes. This layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs. Corresponds roughly with the path control layer of the SNA model Network Management A set of activities and duties whose goal is to provide high-quality,reliable communication among a group of networked computerusers. Typical activities may include resource planning, network design, providing user assistance and training, reconfiguration ofthe network due to a change in user requirements, assessing userneeds and designing appropriate solutions and troubleshootingand remedying network problems as they arise Network Node Server SNA NN that provides resource location and route selection services for ENs, LEN nodes, and LUs that are in its domain Network Number Part of an IP address that specifies the network to which the host belongs Network Operating A term mostly used in DOS networking systems to refer System collectively to the proprietary protocols and network file systemsthat computers use to exchange data with their LAN Servers Network Operator Person who routinely monitors and controls a network, performing tasks such as reviewing and responding to traps, monitoring throughput, configuring new circuits, and resolving problems NFS Network File System. Designed by Sun Microsystems, NFS is now astandard feature of nearly all Unix systems NHRP Next Hop Resolution Protocol. Protocol used by routers to dynamically discover the MAC address of other routers and hosts connected to a NBMA network. These systems can then directly communicate without requiring traffic to use an intermediate hop, increasing performance in ATM, Frame Relay, SMDS, and X. The group responsible for theassignment of IP addresses Network Interface Card. A network adapter on a circuit board that plugs into a computerinternal bus architecture A 16-bit Ethernet chip designed by Texas Instruments NIS Network Information System. Protocol developed by Sun Microsystems for the administration of network-wide databases. Communication standards developed by the ITU-T for baseband networks. Based on 64-kbps B channels and or 64-kbps D channels NIST National institute of Standards and Technology. Formerly the NBS, this U. Individual program that can be loaded into memory and function as part of the NetWare NOS NLSP NetWare Link Services Protocol. Link-state routing protocol bases on IS-IS NMS Network management system. System responsible for managing at least part of a network. An NMS is generally a reasonably powerful and well-equipped computer such as an engineering workstation. NMSs communicate with agents to help keep track of network statistics and resources NMVT Network management vector transport. SNA message consisting of a series of vectors conveying network management-specific information. SNA intermediate node that provides connectivity, directory services, route selection, intermediate session routing, data transport, and network management services to LEN nodes and ENs. The NN contains a CP that manages the resources of both the NN itself and those of the ENs and LEN nodes in its domain. NNs provide intermediate routing services by implementing the APPN PU extensions NNI Network-to-Network Interface. ATM Forum standard that defines the interface between two ATM switches that are both located in a private network or are both located in a public network. The interface between a public switch and private one is defined by the UNI standard. Also, the standard interface between two Frame Relay switches meeting the same criteria NOC Network Operations Center. Organization responsible for maintaining a network Node A networked computing device that takes a protocol address andcan initiate and respond to communication from other networked devices that employ similar protocols Noise Undesirable electrical or electromagnetic signals Nonseed Router In AppleTalk, a router that must first obtain and then verify its configuration with a seed router before it can begin operation Non-stub Area Resource-intensive OSPF area that carries a default route, static routes, intra-area routes, interarea routes, and external routes. Nonstub areas are the only OSPF areas that can have virtual links configured across them and are the only areas that can contain an ASBR Non-Volatile Information that will remain usable by a computer despite loss of power or shutdown Northwest Net NSF-funded regional network serving the Northwestern United States, Alaska, Montana, and North Dakota. Northwest Net connects all major universities in the region, as well as many leading industrial concerns NOS Network operating system. Generic term used to refer to what are really distributed file systems NREN National Research and Education Network. HDLC mode for use on links with one primary station and one or more secondary stations. In this mode, secondary stations can transmit only if they first receive a poll from the primary station NRZ nonreturn to zero. In the Chooser, it is the name that is displayed in the list of devices ODI Open Data-link Interface. A Novell specification for network interface card device drivers that allows multiple protocol stacks to use the same card simultaneously OEM Original Equipment Manufacture. Referring to the subset of the ISO that promotes and defines standards for open networking systems OSI 7-Layer Model A method of describing the relationships between network protocols by grouping them according to the communication functions the protocols provide. The OSI model defines 7 distinct categories Layers that act successively on data as it makes its way between the user and the transmission media OSPF Open Shortest Path First. Also refers to the successor of the Macintosh powered by this chip PPC Process-to-Process Communication Sometimes used as an acronym for PowerPC PPP Point-to-Point Protocol. A specification for synchronous or asynchronous data communication between two routers or between a computer system and a network Precision Referring to the smallest difference in measurement that a test instrument can distinguish PRI Primary Rate Interface. An ISDN service over a T1 link that provides 23 data channels "bearer" or "b" Channels" at 64 KBPS and one 16 KBPS control channel or "D" channel Print Spooler A Software process that accepts a print job from a workstation as if it were a printer and then sends the print job to an actual printer at a later time. There are two styles, a background spooler, where the print spooling process is resident in the same node as the process seeking the print service, and a hardware spooler, where the print spooling process is in a separate node Printer Driver In the Macintosh, a System Extension that is intermediate between the CPU and the printer. While an "application" is a process, that term usually refers to a process that a user can launch from the Finder and directly control, where the use of the term "process" often implies that the process has been launched by the system and is not under direct user control Program A set of instructions that has been coded into a computer language and compiled into a machine language PROM Programmable Read-Only Memory. Firmware in which a chip has had a program "burned in" to its internal circuitry. The designation "EPROM" indicates that the program is Erasable Promiscuous A LAN station that receives and processes all of the packets on its network Proprietary Meaning that information concerning the methods or implementation of a technology are owned by an individual or a company. A group of memory locations that are numerically identified to allow high speed access by a CPU. In random access, any memory location can be accessed at any time by referring to its numerical identifier as compared to sequential access, where memory location 6 can only be accessed after accessing memory locations RARP Reverse Address Resolution Protocol. A method for workstations to ask a server for their IP address during bootstrap operations Reboot A user activity where the user starts a computing device without interrupting its source of electrical power Receiver The node or process for which a packet or other information is intended Remote Access AppleTalk Remote Access. For the IETF, the document that specifies a standard after an exhaustive review process RFS Remote File Sharing. The activity of sharing a file among remote computers Ring A type of network topology where the devices are connected to a continuous conductor RIP Routing Information Protocol. A distance vector routing protocol for IP ROM Read Only Memory. A chip or other electronic device that contains memory that cannot be altered. In the Macintosh, the ROM contains the Macintosh OS and instructions for basic system operations Router A device that forwards packets between networks according to the rules of a network layer protocol such as DDP and information it has gathered during its service concerning the structure of the internet RPC Remote Procedure Call. A command given by one computer to a second computer over a network to execute a defined system call, such as in an NFS session RTT Round Trip Time. The interface between one protocol and another in an adjacent layer Scalability The suitability of a system particularly a network system to operate properly and efficiently when configured on a large scale Screen Saver A background process that monitors system activity such as mouse clicks and key strokes and takes over the system during prolonged periods of idle activity to cover the screen with a display that will prevent damage to its phosphors either by reducing the intensity of electron flow or by displaying an image that changes often enough to avoid screen "burn-in". Some screen savers also offer a security option by requiring a password before a user can regain control of the system Script A set of instructions that a computer can operate. Unlike a program, script instructions are not compiled into machine language but are interpreted by the system at the time of execution. Scripting languages for the Macintosh include HyperTalk, Frontier and AppleScript SCSI Small Computer Systems Interface. A specification ANSI X3T for a short distance meters max. Local Area Network using bus topology for up to eight devices. The Macintosh uses this network for attaching devices such as external disk drives and scanners SDLC Synchronous Data Link Control. Analogous to HDLC Serial Port A port on a computing device that is capable of either transmitting or receiving one bit at a time. A protocol for carrying IP information over serial links SMDS Switched Multimegabit Data Service. A metropolitan area packet switching data network using T-1 and T-3 lines SMI Structure of Management Information SMTP Simple Mail Transfer Protocol. A de facto standard for management of networked devices using a simple request-response data retrieval mechanism SNMPv2 Simple Network Management Protocol Version Offers increased performance, better security, greater portability and greater ability to manage non-network resources Source The node or process transmitting information SONET Synchronous Optical Network. A standard for a worldwide digital network using a common transport. SONET can run over copper or fiber Specification A document that defines a concept and its allowable implementation forms Spike A sudden and transient increase in the voltage from a power supply SPX Sequential Packet Exchange. A Transport layer protocol developed by Novell to provide in-sequence data transfer SQL Structured Query Language. A widely used metalanguage for data base access and management.
The people flee Earth and settle on Mars but have constant conflicts with the native Martians.
England won a splendid harbor, strategically located in the middle of the mainland colonies, and the stately Hudson River penetrating the interior.