Back to top


Backplane Bandwidth

Defines the bandwidth of the module-to-module interconnect in multi-port switches. Backplane speed is just one component of total speed.

Backplane Capacity

Defines the bandwidth of the module-to-module interconnect in multi-port switches. Backplane speed is just one component of total speed.


Also referred to as backpressure flow control, a condition wherein a switch causes a transmitting device to hold off on sending data packets until the switchs bottleneck has been eliminated (i.e., when its buffers holding data have been emptied). In order to create backpressure, the switch either broadcasts false collision detection signals or sends packets back to the originating device if the buffer is full.


The range of frequencies passing through a given circuit. The greater the bandwidth, the more information can be sent through the circuit in a given amount of time.


  1. The original band of frequencies of a signal before it is modulated for transmission at a higher frequency.
  2. A type of data transmission in which digital or analog data is sent over a single unmultiplexed channel, such as an Ethernet LAN. Baseband transmission use TDM to send simultaneous bits of data along the full bandwidth of the transmission channel.


Unit of signaling speed equivalent to the number of discrete conditions or events per second. If each signal event represents only one bit condition, baud rate equals bps (bits per second).

Berkeley Packet Filter

The Berkeley Packet Filter (BPF) is a new architecture for user-level packet capture. BPF provides a raw interface to data link layers in a protocol-independent fashion. All packets on the network, even those destined for other hosts, are accessible through this mechanism.


Bit Error Rate Test/Tester
A device used to test the bit error rate of a communications circuit (i.e. the ratio of received erroneous bits to received bits, usually a number referenced to a power of 10).

Best effort

A QoS class in which no specific traffic parameters and no absolute guarantee are provided. Best effort includes UBR and ABR.


Short for Border Gateway Protocol, an exterior gateway routing protocol that enables groups of routers (called autonomous systems) to share routing information so that efficient, loop-free routes can be established. BGP is commonly used within and between Internet Service Providers (ISPs). The protocol is defined in RFC 1771.


A signaling method (in T1/E1) represents a binary “1” by alternating positive and negative pulses, and a binary “0” by absence of pulses.


The smallest unit of information in a binary system. Represents either a one or zero (“1” or “0”).

Bit Interleaving

Bit Interleaving /Multiplexing
A process used in time division multiplexing where individual bits from different lower speed channel sources are combined (one bit from one channel at a time) into one continuous higher speed bit stream.


A symmetric encryption algorithm designed by Bruce Schneier in 1993 as an alternative to existing encryption algorithms, such as DES. Blowfish is a 64-bit block cipher (i.e., a cryptographic key and algorithm are applied to a block of data rather than single bits) that uses a key length that can vary between 32 and 448 bits. Blowfish is available for free use by any, and the technology is unpatented and free of license.


Short for Basic Link Service, and also called Link Service, it is a Fibre Channel request and response protocol used by all devices.


Bandwidth on Demand
A concept in digital communications that enables users to request additional network bandwidth as the application warrants, allowing them to pay for only the bandwidth they use.


Acronym for bridge protocol data unit. BPDUs are data messages that are exchanged across the switches within an extended LAN that uses a spanning tree protocol topology. BPDU packets contain information on ports, addresses, priorities and costs and ensure that the data ends up where it was intended to go. BPDU messages are exchanged across bridges to detect loops in a network topology. The loops are then removed by shutting down selected bridge interfaces and placing redundant switch ports in a backup, or blocked, state.


Abbreviated as BPL, broadband over power line is a technology that allows Internet data to be transmitted over utility power lines. To use BPL the subscriber needs to use a special broadband modem (phone, cable or satellite) that plugs into an electrical outlet. Internet services are received via radio waves over electrical lines, using many of the same frequencies that are traditionally used for ham radio. There are two types of BPL: in-building BPL technology, which uses the electrical wiring within a building and access BPL, which uses the electrical power distribution grid to provide broadband Internet access.

BPL repeater

In Access broadband over power line (BPL) systems, a BPL repeater is a device used to boost the distance the signal can travel. broadband over power line (BPL). A typical BPL signal travels only for 1,000 to 3,000 feet down line, and a BPL repeater can be used to increase the distance the signal can travel. There is often a decrease in system performance when a repeater is used. Also called a BPL regenerator.


Bits Per Second
A measure of data transmission rate in serial transmission.


Short for Broadband Remote Access Server, it is the aggregation point for the subscriber traffic. It provides aggregation capabilities (e.g. IP, PPP, ATM) between the Regional/Access Network and the NSP or ASP. Beyond aggregation it is also the injection point for policy management and IP QoS in the Regional/Access Networks.


A device interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.


Interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.


The term broadband is used to describe a type of data transmission in which a single medium (wire) can carry several channels at once. Cable TV, for example, uses broadband transmission. In contrast, baseband transmission allows only one signal at a time. Most communications between computers, including the majority of local-area networks, use baseband communications. An exception is B-ISDN networks, which employ broadband transmission.


To simultaneously send the same message to multiple recipients. Broadcasting is a useful feature in e-mail systems. It is also supported by some fax systems. In networking, a distinction is made between broadcasting and multicasting. Broadcasting sends a message to everyone on the network whereas multicasting sends a message to a select list of recipients.

broadcast address

A special type of networking address that is reserved for sending messages to all machines on a given network segment. Generally, a broadcast address is a MAC destination address of all F's.

broadcast storm

A state in which a message that has been broadcast across a network results in even more responses, and each response results in still more responses in a snowball effect. A severe broadcast storm can block all other network traffic, resulting in a network meltdown. Broadcast storms can usually be prevented by carefully configuring a network to block illegal broadcast messages.


Short for bridge router and pronounced BROW-ter, a device that functions as both a router and a bridge. A brouter understands how to route specific types of packets, such as TCP/IP packets. Any other packets it receives are simply forwarded to other network(s) connected to the device (this is the bridge function).


A storage device. Commonly used to compensate for differences in data rates or event timing when transmitting from one device to another. Also used to remove jitter.

buffer overflow

The condition wherein the data transferred to a buffer exceeds the storage capacity of the buffer and some of the data "overflows" into another buffer, one that the data was not intended to go into. Since buffers can only hold a specific amount of data, when that capacity has been reached the data has to flow somewhere else, typically into another buffer, which can corrupt data that is already contained in that buffer.


Used to compensate for differences in data rates or event timing when transmitting from one device to another. Also used to remove jitter.


(n) A set of bits, bytes or characters grouped together for transmission.
(v) An intermittent asynchronous transmission of a specific amount of data. Contrast with streaming.


A transmission path or channel. A bus is typically an electrical connection with one or more conductors, where all attached devices receive all transmissions at the same time.

bus network

A network in which all nodes are connected to a single wire (the bus) that has two endpoints. Ethernet 10Base-2 and 10Base-5 networks, for example, are bus networks. Other common network types include star networks and ring networks.

Bypass Relay Function

Some Ethernet products support bypass relay function on bypass port: When a switch is operating normally, these two bypass ports work in the same way as the other ports. The frame ingressions are processed and then forwarded. In the event, a switch stops working due to a power failure, the bypass relay function will be triggered to ensure non-stop data communication.


A group of bits (normally 8 bits in length).