The Three Error Checking Method? (1 Viewer)

[MonkEE]

Sorry if i post this agian...

But, can some one give me a DETAIL describe of the error checking methods?
/Parity Cheking
/Checksum
/Cyclic Redundancy Check

Dam Heinemann textbook's definition is a blur.

Include info of how it is calculated, and main features (eg. 32-bit, remainder techniques etc...)

any help is appreciated


Bai

 

[honky tonk]

Here are fatmuscle's notes, I hope they help:

Parity:
Refers to a technique of checking whether data has been lost or written over when it's moved from one place in storage to another or when transmitted between computers.
Parity Check, checks for errors using an additional bit called a parity bit. This bit is used only for the purpose of identifying whether the bits being moved have arrived successfully. When data is represented using 7-bit ASCII, then a eighth bit is used that holds a 0 or a 1. When odd parity is chosen then the number of ones in the eight bits must be even. This means that if the number of ones in the first seven digits is even then the parity bit must be 1 to make it odd. If the number of ones in the first 7 bits is off then the parity bit must be zero to keep it odd.

  01010011 for EVEN parity.
  01010010 for ODD parity.

Checksum:
A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, it's assumed that the complete transmission was received.
Checksum, checks the number of bits in a data packet. A data packet is created by dividing the total data into smaller groups. The count of the bits in a data packet is attached to the data packet. It is used by the receiver to check whether all the bits have arrived successfully. If the count matches, it is assumed a complete transmission was received.

CRC (Cyclic Redundancy Check):
Cyclic redundancy checking is a method of checking for errors in data that has been transmitted on a communications link. A sending device applies a 16- or 32-bit polynomial to a block of data that is to be transmitted and appends the resulting cyclic redundancy code (CRC) to the block. The receiving end applies the same polynomial to the data and compares its result with the result appended by the sender. If they agree, the data has been received successfully. If not, the sender can be notified to re-send the block of data.
CRC checks for errors in data transmission using a division process. Data is divided into predetermined lengths and divided by a fixed divisor. The remainder of the calculation is attached and sent with the data. When the data is received, the remainder is recalculated. If the remainders do not match, an error in transmission has occurred.

 

[MonkEE]

woo quick

ok just to clarify a few things:

/Parity check is simple so nvm

/Checksum
Counts the number of bits/8bits (i kno its 8 bit from soemwhere)
= ANS + REMAINDER

Then REMAINDER is send with packet for checking, calculating etc...
is that right?

/CRC
hmm your discription is a bunch of jibberish

well i think its:

Bytes are put together and treat as one number
Two bytes packet: 01110110, 01110110
Treats as one: 01110110 01110110 = x

x is then divided by 16/32-bit to give a remainder
then remainder is sent as error check etc...

right?
get me?

 

[honky tonk]

Originally posted by MonkEE
/Checksum
Counts the number of bits/8bits (i kno its 8 bit from soemwhere)
= ANS + REMAINDER

I could be wrong, but I didn't think the remainder was taken into consideration for the checksum. I thought the total amount of data was divided into smaller groups, the count of bits was attached and checked at the end of transmission..

Originally posted by MonkEE
/CRC
hmm your discription is a bunch of jibberish

Data is divided into predetermined lengths and divided by a fixed divisor. Then, the remainder is sent along with the data. When the data is received, the same division takes place and the remainder is recalculated. If the two remainders do not match, an error has occured.

 

[Huy]

Originally posted by MonkEE
Sorry if i post this agian...
But, can some one give me a DETAIL describe of the error checking methods? Include info of how it is calculated, and main features (eg. 32-bit, remainder techniques etc...)

I believe it was posted before, in another thread. But honky tonk has provided (fatmuscles) notes, which are more than enough (you don't have to know each one in detail, just a general idea of how it works, with the inclusion of techniques used ie addition, polynomial division; remainders).

Originally posted by MonkEE
/Checksum
Counts the number of bits/8bits (i kno its 8 bit from soemwhere)
= ANS + REMAINDER

Then REMAINDER is send with packet for checking, calculating etc...
is that right?

Originally posted by honky tonk
I could be wrong, but I didn't think the remainder was taken into consideration for the checksum. I thought the total amount of data was divided into smaller groups, the count of bits was attached and checked at the end of transmission..

No, you are correct here honky. There is no remainder in checksums (it is a sum, not a divisional process like CRC --to follow). It is as you've said, the total number of bits is counted (check "sum"). Each count of bits is attached to the packet during transmission (naturally) and the end-receiver checks the number of bits, not the remainder by division.

The whole data is divided into smaller packets/groups.
The total number of bits is added and verified.

Correct count = Successful transmission
Incorrect count = Unsuccessful transmission, requiring re-transmission of data packet(s).

/CRC
hmm your discription is a bunch of jibberish

Polynomials are part of the Extension 1 Mathematics course, so I don't think you would understand it if you hadn't (been through) polynomials in Year 10 Advanced Maths.

Data is divided into predetermined lengths and divided by a fixed divisor. Then, the remainder is sent along with the data. When the data is received, the same division takes place and the remainder is recalculated. If the two remainders do not match, an error has occured.

Exactly
P(x) = Q(x).A(x) + R(x)
Polynomial = Quotient x Divisor (and then your remainder).

It's basically what honky said.

"File (all data)" --> split into smaller segments/pieces (slicing a cake into equal parts (the divisor) for a number of people (the predetermined length)).

What's left over ("the crumbs") are then calculated, and compared to each other.

 

[rx72c]

These were asked in the exam and saved my life so for all you next gen yr 12 students, study these hard.

 

[Huy]

It's only a small part though, in the bigger scheme of things.

Know how it works, but don't go into detail eg 32-bit polynomials when divided etc...

Know the differences and advantages

 

[MonkEE]

No, you are correct here honky. There is no remainder in checksums (it is a sum, not a divisional process like CRC --to follow). It is as you've said, the total number of bits is counted (check "sum"). Each count of bits is attached to the packet during transmission (naturally) and the end-receiver checks the number of bits, not the remainder by division.

hmm wellls....

There is a question from some paper (cant remember) but states that both Checksum and CRC uses remainder theorem.

was a multiple choice...

 

[rx72c]

Multiple Choice questions can be wrong

especially if they are not BOS papers

if you dont mind sharing the question with us then we can help tackle your problem.

 

[Huy]

CRC only uses the remainder theorem.

But I wouldn't mind reading the question either