2.2 methods of error detection Flashcards
1
Q
need for error checks
A
errors can occur during data transmission due to interference
2
Q
errors during transmission
A
- data loss
- data gain
- data change
3
Q
error detection methods
A
- parity check (byte/block)
- checksum
- echo check
4
Q
A
4
Q
limitations with parity byte check
A
- two bits may change during transmission: error not found
- identify errors, bit changed not identified
5
Q
describe parity block check
A
- apply parity to rows and columns of data
- identify where error occured
5
Q
describe checksum
A
- whenever block of data needs to be sent, sender calculate checksum value using specific algorithm
- once sent, receiver check checksum again w same alg
- compare received&newly calc
- if no match, arq
6
Q
describe echo check
A
- once data sent, receiver send data back to sender
- sender compare received and original data for errors
7
Q
downside of echo check
A
- dont know if error occured while sending data
- or sending data back for verification
8
Q
use of check digit
A
- detect errors in data entry
9
Q
how does check digit work
A
- calculated from all other digits in data
- check digit would be last digit of code
10
Q
when is check digit used
A
- ISBN
- bar codes
11
Q
what does ISBN stand for
A
international standard book number
12
Q
what is ARQ
A
- automatic repeat query
- use acknowledgements and timeouts to establish that data is received wo errors
- if no errors, positive acknowledgement, if errors, negative
- sender use timeouts, wait pre-determined amt for ack.
- if none received, data sent again
