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B

backbone area — In OSPF, an area that consists of all networks in area ID 0.0.0.0, their attached routers, and all area border routers.

backbone router — OSPF router with all operational interfaces within area 0.0.0.0.

backplane — See midplane.

backup designated router — OSPF router on a broadcast segment that monitors the operation of the designated router and takes over its functions if the designated router fails.

backward explicit congestion notification — See BECN.

BA classifier — Behavior aggregate classifier. A method of classification that operates on a packet as it enters the router. The packet header contents are examined, and this single field determines the class–of–service (CoS) settings applied to the packet. See also multifield classifier.

bandwidth — Range of transmission frequencies a network can use, expressed as the difference between the highest and lowest frequencies of a transmission channel. In computer networks, greater bandwidth indicates a faster data transfer rate capacity.

bandwidth model — In Differentiated-Services-aware traffic engineering, determines the value of the available bandwidth advertised by the interior gateway protocols (IGPs).

bandwidth on demand — A technique to temporarily provide additional capacity on a link to handle bursts in data, videoconferencing, or other variable bit rate applications. Also called flexible bandwidth allocation.

On a Services Router, an ISDN cost-control feature defining the bandwidth threshold that must be reached on links before a Services Router initiates additional ISDN data connections to provide more bandwidth.

base station controller — See BSC.

base station subsystem — See BSS.

Base Station System GPRS Protocol — See BSSGP.

base transceiver station — See BTS.

Basic Rate Interface — See BRI.

BBD — See blade bay data.

B-channel — Bearer channel. A 64–Kbps channel used for voice or data transfer on an ISDN interface. See also D-channel.

bearer channel — See B-channel.

BECN — Backward explicit congestion notification. In a Frame Relay network, a header bit transmitted by the destination device requesting that the source device send data more slowly. BECN minimizes the possibility that packets will be discarded when more packets arrive than can be handled. See also FECN.

behavior aggregate classifier — See BA classifier.

Bellcore — Bell Communications Research. A research and development organization created after the divestiture of the Bell System. It is supported by the regional Bell holding companies (RBHCs), which own the regional Bell operating companies (RBOCs).

Bellman-Ford algorithm — Algorithm used in distance-vector routing protocols to determine the best path to all routes in the network.

BERT — Bit error rate test. A test that can be run on the following interfaces to determine whether they are operating properly: E1, E3, T1, T3, and channelized (DS3, OC3, OC12, and STM1) interfaces.

BFD — Bidirectional forwarding detection. A simple hello mechanism that detects failures in a network. Used with routing protocols to speed up failure detection.

BGP — Border Gateway Protocol. Exterior gateway protocol used to exchange routing information among routers in different autonomous systems.

bidirectional forwarding detection — See BFD.

bit error rate test — See BERT.

bit field match conditions — Use of fields in the header of an IP packet as match criteria in a firewall filter.

bit rate — Number of bits transmitted per second.

BITS — Building Integrated Timing Source. Dedicated timing source that synchronizes all equipment in a particular building.

blade — Routing Engine in the JCS chassis that runs JUNOS software. The JCS chassis holds up to 12 single Routing Engines (or 6 redundant Routing Engine pairs).

blade bay data (BBD) — 60-byte text string stored in the JCS management module NVRAM that conveys configuration information to the Routing Engines (blades) in the JCS chassis.

Blowfish — Unpatented, symmetric cryptographic method developed by Bruce Schneier and used in many commercial and freeware software applications. Blowfish uses variable-length keys of up to 448 bits.

B-MAC — Backbone source and destination MAC address fields found in the IEEE 802.1ah provider MAC encapsulation header.

BOOTP — Bootstrap protocol. A UDP/IP-based protocol that allows a booting host to configure itself dynamically and without user supervision. BOOTP provides a means to notify a host of its assigned IP address, the IP address of a boot server host, and the name of a file to be loaded into memory and executed. Other configuration information, such as the local subnet mask, the local time offset, the addresses of default routers, and the addresses of various Internet servers, can also be communicated to a host using BOOTP.

bootstrap protocol — See BOOTP.

bootstrap router — Single router in a multicast network responsible for distributing candidate rendezvous point information to all PIM-enabled routers.

Border Gateway Protocol — See BGP.

BPDU — Bridge protocol data unit. A Spanning Tree Protocol hello packet that is sent out at intervals to exchange information across bridges and detect loops in a network topology.

BRI — Basic Rate Interface. ISDN interface intended for home and small enterprise applications. BRI consists of two 64-Kbps B-channels to carry voice or data, and one 16-Kbps D-channel for control and signaling. See also B-channel, D-channel.

bridge — Bridge can be either of the following:

Network component defined by the IEEE that forwards frames from one LAN segment or VLAN to another. The bridging function can be contained in a router, LAN switch, or other specialized device. A bridge operates at Layer 2 of the OSI reference model. See also switch.
Device that uses the same communications protocol to connect and pass packets between two network segments.

bridge domain — Set of logical ports that share the same flooding or broadcast characteristics. As in a virtual LAN, a bridge domain spans one or more ports of multiple devices. By default, each bridge domain maintains its own forwarding database of MAC addresses learned from packets received on ports belonging to that bridge domain. See also broadcast domain and VLAN.

bridge protocol data unit — See BPDU.

Broadband services router — See BSR

broadcast — Operation of sending network traffic from one network node to all other network nodes.

broadcast domain — A logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer.

BSC — Base station controller. Key network node in third-generation (3G) systems that supervises the functioning and control of multiple base transceiver stations.

BSR — Broadband services router. A router used for subscriber management and edge routing.

BSS — Base station subsystem. Composed of the base transceiver station (BTS) and base station controller (BSC).

BSSGP — Base Station System GPRS Protocol. Processes routing and quality-of-service (QoS) information for the BSS.

B-TAG — A field defined in the IEEE 802.1ah provider MAC encapsulation header that carries the backbone VLAN identifier information. The format of the B-TAG field is the same as that of the IEEE 802.1ad S-TAG field. See also S-TAG.

BTS — Base transceiver station. Mobile telephony equipment housed in cabinets and colocated with antennas. (Also known as a radio base station.)

buffers — Memory space for handling data in transit. Buffers compensate for differences in processing speed between network devices and handle bursts of data until they can be processed by slower devices.

Building Integrated Timing Source — See BITS.

bundle — Multiple physical links of the same type, such as multiple asynchronous lines, or physical links of different types, such as leased synchronous lines and dial-up asynchronous lines. Collection of software that makes up a JUNOS software release.

B-VID — The specific VLAN identifier carried in a B-TAG.

bypass LSP — Carries traffic for an LSP whose link–protected interface has failed. A bypass LSP uses a different interface and path to reach the same destination.

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