Page 290 - Optical Switching And Networking Handbook

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Glossary 275

Bit The smallest unit of information upon which digital commu-
nications are based; also an electrical or optical pulse that car-
ries this information. It is one binary digit, or a pulse of data.
BITE Built-in test equipment. Features designed into a piece of
equipment that enable an online diagnosis of failures and oper-
ating status.
Bit Error Rate (BER) The number of coding violations detected
in a unit of time, usually one second. Bit Error rate (BER) is cal-
culated with this formula: BER errored bits received/total bits
sent.

Block Error Rate (BLER) One of the underlying concepts of
error performance is the notion of Errored Blocks, that is, blocks
in which one or more bits are in error. A block is a set of consecu-
tive bits associated with the path or section monitored by means
of an Error Detection Code (EDC), such as Bit Interleaved Parity
(BIP). Block Error rate (BLER) is calculated with the formula:
BLER errored blocks received/total blocks sent.
Bit error versus block error Error rate statistics play a key
role in measuring the performance of a network. As errors
increase, user payload (especially data) must be retransmitted.
The end effect is the creation of more (non-revenue) traffic in the
network.

Bit-Interleaved Parity (BIP) A parity check that groups all the
bits in a block into units (such as byte) and then performs a par-
ity check for each bit position in a group.
Bit stuffing In asynchronous systems, a technique used to syn-
chronize asynchronous signals to a common rate before multi-
plexing.
Bit synchronous A way of mapping payload into virtual tribu-
taries (VTs) that synchronizes all inputs into the VTs, but does
not capture any framing information or enable access to subrate
channels carried in each input. For example, bit synchronous
mapping of a channeled DS1 into a VT1.5 does not provide
access to the DS0 channels carried by the DS1.