backbone area

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

backbone router

An OSPF router with all operational interfaces within area


See midplane.

backup designated router

An OSPF router on a broadcast segment that monitors the operation of the designated router and takes over its functions in the event of a failure.

backward explicit congestion notification


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 classification.


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).

base station controller

See BSC.

base station subsystem

See BSS.

Base Station System GPRS Protocol


base transceiver station

See BTS.

Basic Rate Interface

See BRI.


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.


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.


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.


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.


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


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


bit field match conditions

The use of fields in the header of an IP packet as match criteria in a firewall filter.

bit rate

The number of bits transmitted per second.


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


An 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.


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


bootstrap router

The single router in a multicast network responsible for distributing candidate rendezvous point information to all PIM-enabled routers.

Border Gateway Protocol

See BGP.


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.


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 and D-channel.


Device that uses the same communications protocol to connect and pass packets between two network segments. A bridge operates at Layer 2 of the OSI reference model.

bridge protocol data unit



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


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


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


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


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


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



  1. 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.

  3. Collection of software that makes up a JUNOS software release.


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.