Internetworking Terms

Bearer channel. DS0 time slot that carries analog voice or digital data over ISDN. In ISDN, a full-duplex, 64-kbps channel used to send user data. Compare with D channel, E channel, and H channel.

binary 8-zero substitution. Line-code type, used on T1 and E1 circuits, in which a special code is substituted whenever eight consecutive zeros are sent over the link. This code then is interpreted at the remote end of the connection. This technique guarantees ones density independent of the data stream. Sometimes called bipolar 8-zero substitution. Compare with AMI. See also ones density.

Node or software program that provides services to a front end. See also client, FRF.11, and server.

Propagation of network congestion information upstream through an internetwork.

Part of a network that acts as the primary path for traffic that is most often sourced from, and destined for, other networks.

A scheme where telephony signalling is reliably transported from a gateway to a Media Gateway Controller across a packet-switched network.

A scheme, also called signal tunneling, where telephony signals are passed from a gateway to a separate control for processing. The gateway need not interpret the signalling information.

The (usually random) retransmission delay enforced by contentious MAC protocols after a network node with data to transmit determines that the physical medium is already in use.

The physical connection between an interface processor or card and the data buses and the power distribution buses inside a chassis.

See BECN.

See BIB.

Algorithmic process used for routing traffic that surmises information by assuming symmetrical network conditions. For example, if node A receives a packet from node B through intermediate node C, the backward-learning routing algorithm assumes that A can reach B through C optimally.

See BSN.

Bellcore AMA Format. System of abstract syntax and semantics that supports coding of AMA data into records.

In HDLC, a point-to-point network configuration with two combined stations.

See balun.

balanced, unbalanced. Device used for matching impedance between a balanced and an unbalanced line, usually twisted-pair and coaxial cable.

The difference between the highest and lowest frequencies available for network signals. The term also is used to describe the rated throughput capacity of a given network medium or protocol. The frequency range necessary to convey a signal measured in units of hertz (Hz). For example, voice signals typically require approximately 7 kHz of bandwidth and data traffic typically requires approximately 50 kHz of bandwidth.

See bandwidth reservation.

The 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 leg.

See VINES.

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 Francisco), Stanford University, Lawrence Livermore National Laboratory, and NASA Ames Research Center. BARRNet is now part of BBN Planet. See also BBN Planet.

Characteristic of a network technology where only one carrier frequency is used. Ethernet is an example of a baseband network. Also called narrowband. Contrast with broadband.

Compares two similar time ranges in a report format. A baseline time range is protected against purge action so that baseline data is available at report time. The baseline time range can be 1 to 30 days

Bourne-again shell. Interactive UNIX shell based on the traditional Bourne shell, but with increased functionality. See also root account.

See BER.

See BRI.

See BRHR.

Unit of signaling speed equal to the number of discrete signal elements transmitted per second. Baud is synonymous with bits per second (bps) if each signal element represents exactly 1 bit.

See BARRNet.

Bolt, Beranek, and Newman, Inc. High-technology company located in Massachusetts that developed and maintained the ARPANET (and later, the Internet) core gateway system. See also BBN Planet.

Subsidiary company of BBN that operates a nationwide Internet access network composed in part by the former regional networks BARRNet, NEARNET, and SURAnet. See also BARRNet, BBN, NEARNET, and SURAnet.

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. See also Be and CIR.

Best Current Practices. The newest subseries of RFCs that are written to describe BCPs in the Internet. Rather than specifying a protocol, these documents specify the best ways to use the protocols and the best ways to configure options to ensure interoperability between various vendors' products.

Broadband Digital Cross-Connect System. SONET DCS capable of cross-connecting DS-3, STS-1 and STS-3c signals. See also DCS.

excess burst. Negotiated tariff metric in Frame Relay internetworks. The number of bits that a Frame Relay internetwork attempts to transmit after Bc is accommodated. Be data, in general, is delivered with a lower probability than Bc data because Be data can be marked as DE by the network. See also Bc and DE.

Frame from a Token Ring or FDDI device indicating a serious problem with the ring, such as a broken cable. A beacon frame contains the address of the station assumed to be down. See also failure domain.

See B channel.

See BITNET.

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 FE.

See Bellcore.

See BOC.

Bell Communications Research. Organization that performs research and development on behalf of the RBOCs.

See distance vector routing algorithm.

1. bit error rate. Ratio of received bits that contain errors.

2. basic encoding rules. Rules for encoding data units described in the ISO ASN.1 standard. See also ASN.1.

See BIND.

See BSD.

bit error rate tester. Device that determines the BER on a given communications channel. See also BER (bit error rate).

Describes a network system that does not use a sophisticated acknowledgment system to guarantee reliable delivery of information.

Border Gateway Protocol. Interdomain routing protocol that replaces EGP. BGP exchanges reachability information with other BGP systems. It is defined by RFC 1163. See also BGP4 and EGP.

BGP Version 4. 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. See also BGP and CIDR.

burned-in MAC address.

Part of an SS7 MSU that when toggled signals a negative acknowledgment by the remote signaling point.

International Telecommunication Union Telecommunication Standardization Sector (ITU-T) standard that defines the protocols and procedures needed for establishing, maintaining, and terminating broadband switched virtual connections between public networks. Also abbreviated BICI.

Broadband Inter-Carrier Interface. ITU-T standard that defines the protocols and procedures needed for establishing, maintaining, and terminating broadband switched virtual connections between public networks. See also BIC.

See bidir-PIM.

A variant of the Protocol Independent Multicast (PIM) suite of routing protocols for IP multicast. In PIM, packet traffic for a multicast group is routed according to the rules of the mode configured for that multicast group.

See BIGA in the "Cisco Systems Terms and Acronyms" section.

Method of storing or transmitting data in which the most significant bit or byte is presented first. Compare with little-endian.

Numbering system characterized by ones and zeros (1 = on, 0 = off).

See B8ZS.

See AMI.

See BSC.

See bisync.

Berkeley Internet Name Domain. Implementation of DNS developed and distributed by the University of California at Berkeley (United States). Many Internet hosts run BIND, which is the ancestor of many commercial BIND implementations.

Binary Hexadecimal. A method for converting binary files into ASCII for transmission by applications, such as e-mail, that can handle only ASCII.

bit interleaved parity. In ATM, a method used to monitor errors on a link. A check bit or word is sent in the link overhead for the previous block or frame. Bit errors in the payload then can be detected and reported as maintenance information.

Bipolar coding scheme originally developed for use in Ethernet. 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.

Electrical characteristic denoting a circuit with both negative and positive polarity. Contrast with unipolar.

See B8ZS.

See BPV.

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 155 to 622 Mbps and beyond. Contrast with N-ISDN. See also BRI, ISDN, and PRI.

Binary Synchronous Communication Protocol. Character-oriented data-link protocol for applications. Contrast with Synchronous Data Link Control ( SDLC).

Binary digit used in the binary numbering system. Can be 0 or 1.

See BER.

See BERT.

See BIP.

Speed at which bits are transmitted, usually expressed in bits per second.

"Because It's Time" Networking Services. Low-cost, low-speed academic network consisting primarily of IBM mainframes and 9600-bps leased lines. BITNET is now part of CREN. See also CREN.

Dial-up service providing connectivity for members of CREN. See also CREN.

Class of data link layer communication protocols that can transmit frames regardless of frame content. Unlike byte-oriented protocols, bit-oriented protocols provide full-duplex operation and are more efficient and reliable. Compare with byte-oriented protocol.

building integrated timing supply. A clock in a central office that supplies DS1 and/or composite clock timing references to all synchronous network elements in that office.

Abbreviated bps. See also bit rate.

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.

IBM-style channel that implements the FIPS-60 channel, a U.S. channel standard. This channel also is referred to as OEMI channel and 370 block mux channel.

See BSS.

In a switching system, a condition in which no paths are available to complete a circuit. The term also is used to describe a situation in which one activity cannot begin until another is completed.

An internal cooling fan used in larger router and switch chassis.

bidirectional line switch ring. SONET ring architecture that provides working and protection fibers between nodes. If the working fiber between nodes is cut, traffic is routed automatically onto the protection fiber. See also SONET.

The standard connector used to connect IEEE 802.3 10Base2 coaxial cable to an MAU.

Broadband Network Interface.

Broadband Network Module.

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. Also called boundary node.

See BOBI in the "Cisco Systems Terms and Acronyms" section.

Bell operating company. Twenty-two local phone companies formed by the breakup of AT&T. See also RBOC.

See BBN.

Minimum-function Cisco IOS image that serves only to boot the full-function, operational Cisco IOS image. Also known as rxboot.

See boot PROM.

boot programmable read-only memory. A chip mounted on a printed circuit board used to provide executable boot instructions to a computer device.

Separate Flash memory device used primarily to store the Cisco IOS boot helper image, operational Cisco IOS images, and system configuration information.

Bootstrap Protocol. The protocol used by a network node to determine the IP address of its Ethernet interfaces to affect network booting.

See BOOTP.

A router that communicates with routers in other autonomous systems.

See BGP.

Node in one zone that connects with one or more nodes in other zones.

Capability of SNA subarea nodes to provide protocol support for attached peripheral nodes. Typically found in IBM 3745 devices.

See BNN.

See BNN.

Bridge Protocol Data Unit. Spanning-Tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network. See also PDU.

baseline privacy interface.

bits per second.

bipolar violation. A one (1) in a bipolar signal that has the same polarity as the preceding one. See also coding violation.

See BPX Service Node in the "Cisco Systems Terms and Acronyms" section.

basic rate access. Two 64 kbps B channels + one 16 kbps D channel (2B + D), carrying user traffic and signaling information respectively to the user via twisted pair local loop.

See BOBI in the "Cisco Systems Terms and Acronyms" section.

bridge relay function.

Basic Research and Human Resources. Component of the HPCC program designed to support research, training, and education in computer science, computer engineering, and computational science. See also HPCC.

Basic Rate Interface. ISDN interface composed of two B channels and one D channel for circuit-switched communication of voice, video, and data. Compare with PRI. See also BISDN, ISDN, and N-ISDN.

Device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (Layer 2) of the OSI reference model. In general, a bridge filters, forwards, or floods an incoming frame based on the MAC address of that frame. See also relay.

A process that uses entries in a filtering database to determine whether frames with a given MAC destination address can be forwarded to a given port or ports. Described in the IEEE 802.1 standard. See also IEEE 802.1.

A bridging feature that assigns network interfaces to a particular spanning-tree group. Bridge groups can be compatible with the IEEE 802.1 or the DEC specification.

A number that identifies each bridge in an SRB LAN. Parallel bridges must have different bridge numbers.

See Bpdu.

The 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 802.1 standard. See also IEEE 802.1.

See BVI.

A group of interfaces bridged together to emulate a multiport bridge.

Describes facilities or services that operate at the DS3 rate and above. For example, a Broadband DCS makes cross-connections at the DS3, STS-1, and STS-Nc levels. Similarly, Broadband ISDN provides about 150 Mb/s per channel of usable bandwidth.

1. Transmission system that multiplexes multiple independent signals onto one cable.

2. Telecommunications terminology: Any channel having a bandwidth greater than a voice-grade channel (4 kHz).

3. LAN terminology: A coaxial cable on which analog signaling is used. An RF system with a constant data rate at or above 1.5 Mbps. Also called wideband. Contrast with baseband.

See BIC.

See BISDN.

See BNI.

See BNM.

See BXM.

Data packet that are sent to all nodes on a network. Broadcasts are identified by a broadcast address. Compare with multicast and unicast. See also broadcast.

A 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. See also broadcast.

See BUS.

Set of all devices that receive broadcast frames originating from any device within the set. Broadcast domains typically are bounded by routers because routers do not forward broadcast frames.

The propagation of a search request to all network nodes if the location of a resource is unknown to the requester. See also directed search.

An 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.

Concatenation of "bridge" and "router." Used to refer to devices that perform both bridging and routing functions.

GUI-based hypertext client application, such as Internet Explorer, Mosaic, and Netscape Navigator, used to access hypertext documents and other services located on innumerable remote servers throughout the WWW and Internet. See also hypertext, Internet, Mosaic, and WWW.

1. binary synchronous communication. Character-oriented data link layer protocol for half-duplex applications. A form of telecommunication line control that uses a standard set of transmission control characters and control character sequences, for the binary synchronous transmission of binary-coded data between stations.

2. base station controller. In wireless, provides the control functions and physical links between the MSC and BTS in a GSM mobile wireless network. The BSC controls the interface between the SGSN and the BTS in a GPRS network. The BSC is a high-capacity telephony switch that provides handsoff functions and cell configuration data, and controls radio frequency power levels in BTSs. The combined functions of the BSC and the BTS are referred to as the BSS.

Berkeley Standard Distribution. A term used to describe any of a variety of UNIX-type operating systems based on the UC Berkeley BSD operating system.

Part of an SS7 MSU that acknowledges the receipt of signal units by the remote signalling point. Contains the sequence number of the signal unit being acknowledged.

base station subsystem. Refers to the radio-related functions provided by the BTS and BSC in a GSM mobile wireless network.

Block Serial Tunnel.

Note: Do not use bisync serial tunnel or BSC tunnel as synonyms.

burst tolerance. A parameter defined by the ATM Forum for ATM traffic management. For VBR connections, BT determines the size of the maximum burst of contiguous cells that can be transmitted. See also VBR.

Basic Trading Area. An area or "footprint" in which an entity is licensed to transmit their frequencies. BTAs were established by Rand McNally and are defined as county lines. Rand McNally licensed their mapping data to the FCC for ease of designation for site licenses.

base transceiver station. A land-based station in a GSM mobile wireless network that consists of transceivers and antennas, which handle the radio interface to a mobile station. A BSC controls one or more BTSs. The combined functions of the BTS and the BSC are referred to as the BSS.

British thermal units.

by the way. One of many short-hand phrases used in chat sessions and e-mail conversations. See also IMHO.

A storage area used for handling data in transit. Buffers are used in internetworking to compensate for differences in processing speed between network devices. Bursts of data can be stored in buffers until they can be handled by slower processing devices. Sometimes referred to as a packet buffer.

To create flat files that are ready for use by the signaling controller database.

See BITS.

In data communications, a sequence of signals counted as one unit in accordance with some specific criterion or measure.

See BT.

A data communications term referring to an uneven pattern of data transmission.

1. Common physical signal path composed of wires or other media across which signals can be sent from one part of a computer to another. Sometimes called a highway.

2. See bus topology.

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. See also ELAN.

IBM channel, developed in the 1960s, incorporating copper multiwire technology. Replaced by the ESCON channel. See also ESCON channel and parallel channel.

See BIGA in the "Cisco Systems Terms and Acronyms" section.

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.

Bridge Group Virtual Interface. Logical Layer 3-only interface associated with a bridge group when IRB is configured.

AT&T implementation of X.25. See also X.25.

broadband switch module. ATM port card for the Cisco BPX switch.

The operating mode on FDDI and Token Ring networks in which an interface has been removed from the ring.

Allows a particular Token Ring interface to be shut down and thus effectively removed from the ring.

A term used to refer to a series of consecutive binary digits that are operated upon as a unit (for example, an 8-bit byte).

The process of storing numeric data with the least-significant byte first. Used for integers and addresses on devices with Intel microprocessors.

A class of data-link communications protocols that use a specific character from the user character set to delimit frames. These protocols largely have been replaced by bit-oriented protocols. Compare with bit-oriented protocol.