7. data link layer error detection and correction codes - parity and checksum

1. Communication
Networks
- Data Link Layer
[Error Detection
& Correction Codes]
Parity Bits and Checksum

2. Video Lectures for these Slides are
available at
www.youtube.com/GURUKULA

3. Need for Error Detection and Correction
• For most applications, a system must
guarantee that the data received are
identical to the data transmitted.
• Any time data are transmitted from
one node to the next, they can become
corrupted in passage.
• Many factors can alter one or more
bits of a message.
• Some applications require a
mechanism for detecting and
correcting errors.

4. Types of Errors
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• The term single-bit error means that only 1 bit of a given data unit
is changed from 1 to 0 or from 0 to 1.
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• The term burst error means that 2 or more bits in the data unit
have changed from 1 to 0 or from 0 to 1.

5. Concept of Redundancy
Redundant:
Data that are able to be omitted
without loss of meaning or
function.
Process of adding REDUNDANT
bits to the Data so as to detect the
occurrence of errors

6. Difference
S.No Error Detection Error Correction
1
In error detection, we are only
looking to see if any error
has occurred. The answer is a
simple yes or no.
In error correction, we need to know the
exact number of bits that are
corrupted and, more importantly, their
location in the message.
2
We are not even interested in the
number of corrupted bits.
The number of errors and the size of the
message are important factors.

7. Error Detection Codes
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Error Correction Codes
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8. 1. Parity Bits - One Dimensional Parity
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1. Parity Bits - Two Dimensional Parity

10. 2. Checksum
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11. Checksum - Algorithm

12. Sender Site Algorithm
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13. Receiver site Algorithm
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14. Checksum - Example Explanation Video Available at
www.youtube.com/GURUKULA

15. Pros and Cons of Checksum:
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16. References:
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