1. PREPARED BY: ENGR. JO-ANN C. VIÑAS
MODULE 7
ERROR DETECTION
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

2. PREPARED BY: ENGR. JO-ANN C. VIÑAS
TRANSMISSION ERRORS
Transmission errors are caused by:
thermal noise {Shannon}
impulse noise (e..g, arcing relays)
signal distortion during transmission (attenuation)
crosstalk
voice amplitude signal compression (companding)
quantization noise (PCM)
jitter (variations in signal timings)
receiver and transmitter out of synch
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

3. PREPARED BY: ENGR. JO-ANN C. VIÑAS
OBJECTIVES:
1. Introduce Data Communications
2. Define Data Communication Codes
3. Discuss the Types of Data Transmission and
Types of Errors
4. Explain Error Detection Schemes
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

4. PREPARED BY: ENGR. JO-ANN C. VIÑAS
DATA COMMUNICATIONS
- It is the process of transferring digital information (usually binary form) between two or more points
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

5. PREPARED BY: ENGR. JO-ANN C. VIÑAS
FORMS OF DATA
a. Alphabetical information
b. Numeric information
c. Symbolic information
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

6. PREPARED BY: ENGR. JO-ANN C. VIÑAS
DATA CODE
- is a set of rules that translates alphanumeric characters into binary numbers
- also called character codes, character sets, character languages or symbol codes
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

7. DATA COMMUNICATION CODES
1. Baudot Code
- 1st fixed-length character
- developed for machine rather than people
bit character code primarily used for low speed teletype system equipment
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

8. DATA COMMUNICATION CODES
2. ASCII Code (American Standard for Information Interchange)
- 7-bit fixed length character set
- is the standard character set for source coding the alphanumeric character set that humans understand but computers do not.
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

9. DATA COMMUNICATION CODES
3. EBCDIC Code (Extended Binary-Coded Decimal Interchange Code)
- 8-bit fixed length character set developed in by IBM
- used almost exclusively with IBM mainframe computers and peripheral equipment
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

10. DATA COMMUNICATION CODES
4. Bar Codes
- is a series of vertical black bars separated by vertical white bars (called spaces)
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

11. SERIAL and PARALLEL DATA TRANSMISSION
1. Parallel by bit or Serial by character
2. Serial by bit
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

12. SERIAL DATA TRANSMISSION
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

13. PARALLEL DATA TRANSMISSION
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

14. PREPARED BY: ENGR. JO-ANN C. VIÑAS
TYPES OR ERRORS
1. Single bit error
- 1 bit of error has occurred
2. Burst error
- 2 or more bits in the data unit have changed from 1 to 0 or from 0 to 1
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

15. PREPARED BY: ENGR. JO-ANN C. VIÑAS
SINGLE BIT ERROR
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

16. PREPARED BY: ENGR. JO-ANN C. VIÑAS
BURST ERROR
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

17. PREPARED BY: ENGR. JO-ANN C. VIÑAS
“Error detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination.”
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

18. PREPARED BY: ENGR. JO-ANN C. VIÑAS
ERROR DETECTION
- Is the process of monitoring data transmission and determining when errors have occurred.
Purpose:
“ Not to prevent error from occurring but to prevent UNDETECTED ERROR.”
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

19. GENERAL ERROR DETECTION SYSTEM
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

20. ERROR DETECTION METHODS
1. REDUNDANCY
- Transmitting each character twice
2. EXACT COUNT ENCODING
- The number of 1’s in each character is the same
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

21. PREPARED BY: ENGR. JO-ANN C. VIÑAS
REDUNDANCY
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

22. PREPARED BY: ENGR. JO-ANN C. VIÑAS
PARITY BIT
- Bit added to each character to make all bits add up to an even number (even parity) or odd number (odd parity)
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

23. PREPARED BY: ENGR. JO-ANN C. VIÑAS
EVEN PARITY CONCEPT
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

24. PREPARED BY: ENGR. JO-ANN C. VIÑAS
“Simple parity check can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.”
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

25. ERROR DETECTION METHODS
3. PARITY CHECKING
- adds 1 additional bit to each byte in the message
A) Odd Parity
B) Even Parity
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

26. PREPARED BY: ENGR. JO-ANN C. VIÑAS
PARITY GENERATORS
I. Serial Transmission Parity Generator
II. Parallel Transmission Parity Generator
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

27. SERIAL TRANSMISSION PARITY GENERATOR
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

28. PARALLEL TRANSMISSION PARITY GENERATOR
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29. PREPARED BY: ENGR. JO-ANN C. VIÑAS
PARITY CHECKING
Advantage:
1. Simple
Disadvantages:
1. If even number of errors has occurred it can not be detected
2. 50% efficiency
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

30. ERROR DETECTION METHODS
4. VRC/LRC
A) LRC - message parity
B) VRC - character parity
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

31. VERTICAL REDUNDANCY CHECKING
VRC entails the appending of a parity bit at the end of each transmitted character of value to create an odd or even total mathematical bit value.
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

32. LONGITUDINAL REDUNDANCY CHECKING OR BLOCK CHECKING CHARACTER
LRC adds another level of reliability, as data is viewed in a block or data set, as though the receiving device were viewing data set in a matrix format.
LRC adds a significant measure of reliability. Also known as checksum, the LRC is sent as an extra character at the end of each data block.
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

33. PREPARED BY: ENGR. JO-ANN C. VIÑAS
VRC/LRC
Advantage:
1. Simple
2. 98% reliability
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

34. PREPARED BY: ENGR. JO-ANN C. VIÑAS
EXAMPLE
Determine the VRC and LRC for the message “SANTINO”. Use ASCII Character, and also use odd parity for VRC and even parity for LRC. Determine What ASCII character is to be transmitted for checking the message.
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

35. PREPARED BY: ENGR. JO-ANN C. VIÑAS
“In two-dimensional parity check, a block of bits is divided into rows and a redundant row of bits is added to the whole block.”
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

36. ERROR DETECTION METHODS
5. CRC
- Is generally used with 8-bit codes such as EBCDIC.
- CRC 16: most common used CRC code in US and is identical to CCITT V.41
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

37. CRC GENERATING CIRCUIT
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38. PREPARED BY: ENGR. JO-ANN C. VIÑAS
CRC GENERATOR
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

39. ERROR DETECTION METHODS
5. CRC
- CRC Character is the remainder of a division process.
G(x) - data message
P(x) - generator polynomial function
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

40. ERROR DETECTION METHODS
CRC 16
P(x) = x16 + x12 + x5 + x0
Advantage:
% efficiency
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

41. PREPARED BY: ENGR. JO-ANN C. VIÑAS
CRC ALGORITHM
1. Multiply G(x) by xn-k (puts zeros in (n-k) low order positions)
2. Divide xn-k G(x) by P(x)
3. Add remainder B(x) to xn-k G(x) (puts check bits in the n-k low order positions):
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

42. PREPARED BY: ENGR. JO-ANN C. VIÑAS
CRC CHECKING
1. Add the CRC to the end of G(x)
2. Divide the product obtained in Step 1 by P(x)
“The remainder of the process should be equal to 0, otherwise error has occurred.”
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

43. PREPARED BY: ENGR. JO-ANN C. VIÑAS
EXAMPLE
Determine the BCS for the ff data and CRC generating polynomials.
G(x) = x7 + x5 + x4 + x2 + x1 + x0
P(x) = x5 + x4 + x1 + x0
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

44. MOST COMMONLY USED CYCLIC CODES GENERATOR POLYNOMIAL
CRC-12 : x12 + X11 + X3 + X2 + X + 1
CRC-16: x16 + x 15 + x2 + 1
CRC-CCITT: x16 + x12 + x5 + 1
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PREPARED BY: ENGR. JO-ANN C. VIÑAS

45. PREPARED BY: ENGR. JO-ANN C. VIÑAS
DATA UNIT AND CHECKSUM
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

46. PREPARED BY: ENGR. JO-ANN C. VIÑAS
6. CHECKSUM
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

47. CHECKSUM ALGORITHM AT THE SENDER
The sender follows these steps:
The unit is divided into k sections, each of n bits.
All sections are added using one’s complement to get the sum.
The sum is complemented and becomes the checksum.
The checksum is sent with the data.
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

48. CHECKSUM ALGORITHM AT THE RECEIVER
The receiver follows these steps:
The unit is divided into k sections, each of n bits.
All sections are added using one’s complement to get the sum.
The sum is complemented.
If the result is zero, the data are accepted: otherwise, rejected.
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

49. PREPARED BY: ENGR. JO-ANN C. VIÑAS
EXAMPLE
Suppose the following block of 16 bits is to be sent using a checksum of 8 bits.
Determine the checksum.
Prove that the receiver can detect the error.
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS

50. PREPARED BY: ENGR. JO-ANN C. VIÑAS
EXAMPLE
Now suppose there is a burst error of length 5 that affects 4 bits.
Prove that the receiver can detect the error.
4/18
PREPARED BY: ENGR. JO-ANN C. VIÑAS