Error Detection Approaches

1. Mr. Vipul H. Kondekar
(vhkondekar@witsolapur.org)
Assistant Professor,
Electronics & Telecommunication Engineering
Walchand Institute of Technology, Solapur
(www.witsolapur.org)
Error Detection:
Cyclic Redundancy Check
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2. At the end of this session, students will be able to
1) Differentiate between Error detection and Error correction.
2) Calculate CRC code for given Data and Generator Polynomial.
3) Identify the presence of Error using CRC.
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Learning Outcomes

3. Contents
❑ Introduction
❑ Error Detecting/Correcting
❑ Cyclic Redundancy Check
❑ Generator Polynomials
❑ Division in CRC Encoder
❑ Division in CRC Decoder
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Error Correcting/Detecting Codes
• Error correction
▪ Referred to as forward error correction
▪ Detect and correct error
• Error detection
▪ Detect error and request retransmission
• Redundancy added to message
Codeword (n bits)
message + redundancy
(m bits) (r bits)
n = m + r

5. Error correcting or error detecting?
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Think ?

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Cyclic Redundancy Check
• view data bits, D, as a binary number
• choose r+1 bit pattern (generator), G
• goal: choose r CRC bits, R, such that
– <D,R> exactly divisible by G (modulo 2)
– receiver knows G, divides <D,R> by G. If non-zero remainder:
error detected!
– can detect all burst errors less than r+1 bits
• widely used in practice (Ethernet, 802.11 WiFi, ATM)

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Cyclic Redundancy Check

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Generator Polynomial
Standard Polynomials

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Division in CRC encoder

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Division in the CRC decoder for two cases

11. References
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• Data communication- B.A. Forouzan 4th Edition Tata Mc Graw hill
Publication.
• TCP/IP protocol suit- B.A. Forouzan 4th Edition Tata Mc Graw hill
Publication.
• Computer Networking, J. Kurose & K. Ross
• Computer networks- Andrew S.Tanenbaum
• Internetworking TCP/IP Principal, Protocol and Architecture -Douglas Comer-
Addision -Wesley
• TCP/IP Illustrated, The Protocols – W. Richard Slevens, G.Gabrani –PE pub.
• Data and computer communication – William Stallings. - PE pub.

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Thanks!!