2.2 methods of error detection Flashcards
1
Q
what are methods of error detection
A
- parity byte check
- parity block check
- checksum
- echo check
2
Q
how does parity check work
A
make MSB 1 or 0 so that all bits add up to odd/even (depending on odd/even parity)
3
Q
- of parity check
A
- cant detect transposition errors (when bit in given byte switched from 1 to 0 vv)
4
Q
what is parity block
A
- same rules as for normal parity checks
- takes set of binary numbers and arranges in table so parity bit used in each row/column
5
Q
how does checksum work
A
- value calculated from data using an algorithm
- value transmitted with data
- value recalculated by receiver using same algorithm
- if checksum values diff, there is error
6
Q
how does echo check work
A
- receiving computer sends exact copy of data received to sending computer
- sending computer performs error checking
7
Q
disadvantages of echo check
A
- hard to tell if data was corrupted in transit to destination or way back
- very slow
8
Q
what erros can check digit identify
A
- transposition errors
- incorrect digits
- extra/omitted digits
9
Q
examples of uses of check digit
A
- ISBN
- barcodes
- Vehicle Identification Number (VIN)
10
Q
what is transposition error
A
when 2 bits are accidentally swapped
11
Q
what does ARQ stand for
A
automatic repeat query
12
Q
how does ARQ work
A
- if error detected ARQ sent
- request sending computer to resend data
- repeat until no errors detected
