IBM SAN32M1, Installation And Service Manual

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531 Glossary
backbone Cable on which two or more stations or networks may be attached,
typically used to link computer networks at one site with those at
another. Smaller branch networks are sometimes called ribs.
backplane
The backplane provides direct current (DC) power distribution and
connections for all logic cards.
backup
field-replaceable unit
Backup FRU. When an active FRU fails, an identical backup FRU
takes over operation automatically (failover) to maintain director or
switch and Fibre Channel link operation. See also
active field-replace-
able unit .
backup FRU See backup field-replaceable unit .
bandwidth (1) The amount of data that can be sent over a given circuit. (2) A
measure of how fast a network can move information, usually mea-
sured in Hertz (Hz).
baud
The unit of signaling speed, expressed as the maximum number of
times per second the signal can change the state of the transmission
line or other medium. The units of baud are seconds to the negative 1
power. Note: With Fibre Channel scheme, a signal event represents a
single transmission bit.
BB_Credit See buffer-to-buffer credit .
beaconing Use of light-emitting diodes (LEDs) on ports, port cards,
field-replaceable units (FRUs), and directors to aid in the fault-isola-
tion process. When enabled, active beaconing will cause LEDs to flash
in order for the user to locate field-replaceable units (FRU’s),
switches, or directors in cabinets or computer rooms.
ber See bit error rate .
bezel A removable panel that covers empty drive bays and port cards.
bidirectional In Fibre Channel protocol, the capability to simultaneously communi-
cate at maximum speeds in both directions over a link.
bit
Abbreviated as b. (1) Binary digit, the smallest unit of data in comput-
ing, with a value of zero or one (D). (2) A bit is the basic data unit of
all digital computers. It is usually part of a data byte or data word;
however, a single bit can be used to control or read logic ON/OFF
functions. (3) A bit is a single digit in a binary number. Bits are the