| | podobné slovo | definícia |
cyclic redundancy check
(encz) | cyclic redundancy check, n: |
cyclic redundancy check
(wn) | cyclic redundancy check
n 1: an error correction code that is recorded in each sector of
a magnetic disk and used to catch errors in the data |
block redundancy check
(foldoc) | Longitudinal Redundancy Check
Block Redundancy Check
LRC
(LRC, Block Redundancy Check) An
error checking method that generates a longitudinal parity
byte from a specified string or block of bytes on a
longitudinal track.
The longitudinal parity byte is created by placing individual
bytes of a string in a two-dimensional array and performing
a Vertical Redundancy Check vertically and horizontally on
the array, creating an extra byte. This is an improvement
over the VRC because it will catch two errors in the
individual characters of the string, beyond the odd errors.
(2004-01-26)
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cyclic redundancy check
(foldoc) | cyclic redundancy check
CRC
cyclic redundancy code
(CRC or "cyclic redundancy code") A number derived
from, and stored or transmitted with, a block of data in order
to detect corruption. By recalculating the CRC and comparing
it to the value originally transmitted, the receiver can
detect some types of transmission errors.
A CRC is more complicated than a checksum. It is calculated
using division either using shifts and exclusive ORs or
table lookup (modulo 256 or 65536).
The CRC is "redundant" in that it adds no information. A
single corrupted bit in the data will result in a one bit
change in the calculated CRC but multiple corrupted bits may
cancel each other out.
CRCs treat blocks of input bits as coefficient-sets for
polynomials. E.g., binary 10100000 implies the polynomial:
1*x^7 + 0*x^6 + 1*x^5 + 0*x^4 + 0*x^3 + 0*x^2 + 0*x^1 + 0*x^0.
This is the "message polynomial". A second polynomial, with
constant coefficients, is called the "generator polynomial".
This is divided into the message polynomial, giving a quotient
and remainder. The coefficients of the remainder form the
bits of the final CRC. So, an order-33 generator polynomial
is necessary to generate a 32-bit CRC. The exact bit-set used
for the generator polynomial will naturally affect the CRC
that is computed.
Most CRC implementations seem to operate 8 bits at a time by
building a table of 256 entries, representing all 256 possible
8-bit byte combinations, and determining the effect that each
byte will have. CRCs are then computed using an input byte to
select a 16- or 32-bit value from the table. This value is
then used to update the CRC.
Ethernet packets have a 32-bit CRC. Many disk formats
include a CRC at some level.
(1997-08-02)
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longitudinal redundancy check
(foldoc) | Longitudinal Redundancy Check
Block Redundancy Check
LRC
(LRC, Block Redundancy Check) An
error checking method that generates a longitudinal parity
byte from a specified string or block of bytes on a
longitudinal track.
The longitudinal parity byte is created by placing individual
bytes of a string in a two-dimensional array and performing
a Vertical Redundancy Check vertically and horizontally on
the array, creating an extra byte. This is an improvement
over the VRC because it will catch two errors in the
individual characters of the string, beyond the odd errors.
(2004-01-26)
|
vertical redundancy check
(foldoc) | Vertical Redundancy Check
VRC
(VRC) An error checking method
performed on one 8-bit ASCII character, where the 8th bit is
used as the parity bit.
The resulting parity bit is constructed by XORing the
word. The result is a "1" if there is an odd number of 1s,
and a "0" if there is an even number of 1s in the word. This
method is unreliable because if an odd number of bits are
distorted, the check will not detect the error. The
Longitudinal Redundancy Check is an improvement.
(2001-04-28)
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