Data Communications and Networking

1. NETWORK
DATA LINK LAYER-ERROR CORECTION AND DECTECTION
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Prepared by: Mir Omranudin Abhar
Email : MirOmran@Gmail.com
Fall ,2019

2. [Error]
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The data can be corrupted during transmission (from source to receiver). It
may be affected by external noise or some other physical imperfections. In
this case, the input data is not same as the received output data. This
mismatched data is called “Error”.

3. [Error]-[Types Of Errors]
1. Single bit errors
2. Multiple bit errors
3. Burst errors
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4. [Error]-[Types Of Errors]-
[Single bit errors]
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In a frame, there is only one bit, anywhere though, which is corrupt.

5. [Error]-[Types Of Errors]-
[Multiple bit errors]
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Frame is received with more than one bits in corrupted state.

6. [Error]-[Types Of Errors]-
[Burst errors]
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Frame contains more than1 consecutive bits corrupted.

7. [Error]-[Error Detecting Codes]
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Types of Error detection
1. Parity Checking
2. Cyclic Redundancy Check (CRC)
3. Longitudinal Redundancy Check (LRC)
4. Check Sum

8. [Error]-[Error Detecting Codes]-
[Parity Checking]
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1. Even Parity
2. Odd Parity

9. [Error]-[Error Detecting Codes]-
[Cyclic Redundancy Check (CRC)]
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10. [Error]-[Error Detecting Codes]-
[Cyclic Redundancy Check (CRC)]
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X Y X ⊕ Y
0 0 0
0 1 1
1 0 1
1 1 0

11. [Error]-[Error Detecting Codes]-
[Longitudinal Redundancy Check (LRC)]
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12. [Error]-[Error Detecting Codes]-
[Check Sum]
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Sender

13. [Error]-[Error Detecting Codes]-
[Check Sum]
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Recevier

14. [Error]-[Error Correction ]
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Error Correction can be handled in two ways:
1. Backward error correction: Once the error is discovered, the
receiver requests the sender to retransmit the entire data unit.
2. Forward error correction: In this case, the receiver uses the error-
correcting code which automatically corrects the errors.

15. [Error]-[Error Correction]-
[Hamming Code]
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The key to the hamming Code is the use of extra parity bits to allow
the identification of a single error.
Example : 10011010
Now we are going to create data word including parity bits. All bit
positions that are powers of 2 is our parity bits(ie: 1,2,3,4,16 etc)

16. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010

17. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010

18. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010

19. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010
Error :
10011110

20. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010
Error :
10011110
Detection and Correction

21. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010
Error :
10011110
Detection and Correction

22. [Error]-[Error Correction]-
[Hamming Code]
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Example :
10011010
Error :
10011110
Detection and Correction

23. [Error]-[Error Correction]-
[Hamming Code]
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24. [Error]-[Error Correction]-
[Hamming Code]
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25. [Error]-[Error Correction]-
[Hamming Code]
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26. [Error]-[Error Correction]-
[Hamming Code]
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27. Question
.1
‫در‬
‫مورد‬
‫تکنالوژی‬
Wifi
‫معلومات‬
‫ید؟‬‫ه‬‫بد‬
.2
‫تفاوت‬
‫بنی‬
‫رمزگذاری‬
WPA , WEP & WPA2
‫در‬
‫تکنالوژی‬
wifi
‫در‬
‫ست؟‬‫چی‬
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