Certain types of errors cannot be detected by error detection algorithms.
1. Two-dimensional parity cannot detect few 4-bit errors or errors of 5 bits or more. CRC can detect errors up to 32 bits.
2. Checksums cannot detect errors where two data items are exchanged or a data item value is increased and another is decreased by the same amount.
3. CRC cannot detect all burst errors affecting an even number of bits, or burst errors longer than the polynomial degree. More complex algorithms like CRC are needed for safe transmission.
Cyclic Redundancy Codes (CRCs) provide a first line of defense against data corruption in many networks. Unfortunately, many commonly used CRC polynomials provide significantly less error detection capability than they might. An exhaustive exploration reveals that most previously published CRC polynomials are either inferior to alternatives or are only good choices for particular message lengths.
Cyclic Redundancy Codes (CRCs) provide a first line of defense against data corruption in many networks. Unfortunately, many commonly used CRC polynomials provide significantly less error detection capability than they might. An exhaustive exploration reveals that most previously published CRC polynomials are either inferior to alternatives or are only good choices for particular message lengths.
to transfer data in network from one device to another with acceptable accuracy, so the system must guarantee the transmitted data should be identical to received data.
there should be no errors if any error occurs in how many ways it can be detected and corrected
This presentation is about controlling error in network layer made during the transmission of data.
It's tells the way by which we can control and correct the noisy code
These slides explain more about types of errors in Data communication, issues of parity check , and redundancy .
also it includes some solutions of questions based on data communication
Key Management, Diffie-Hellman Key Exchange, Elliptic Curve Arithmetic, Elliptic Curve
Cryptography, Message Authentication and Hash Functions, Hash and MAC Algorithms
Digital Signatures and Authentication Protocols
to transfer data in network from one device to another with acceptable accuracy, so the system must guarantee the transmitted data should be identical to received data.
there should be no errors if any error occurs in how many ways it can be detected and corrected
This presentation is about controlling error in network layer made during the transmission of data.
It's tells the way by which we can control and correct the noisy code
These slides explain more about types of errors in Data communication, issues of parity check , and redundancy .
also it includes some solutions of questions based on data communication
Key Management, Diffie-Hellman Key Exchange, Elliptic Curve Arithmetic, Elliptic Curve
Cryptography, Message Authentication and Hash Functions, Hash and MAC Algorithms
Digital Signatures and Authentication Protocols
Module 1 computer networks imtroduction,data link layerDeepak John
Computer Networks Notes- Networking Concepts: Classification of networks: LAN, MAN, WAN and the Internet. Protocols and protocol architecture. The OSI ref. Model, TCP/IP ref. model, its origin, the Internet layer, the TCP layer, the application layer Comparison of the OSI and TCP/IP ref. models. A critiques of the OSI model and protocols, A critique of the TCP/IP ref. model, Novel Netware.
Data Link Layer: Need for data link control, Frame synchronization - flag fields, bit stuffing, flow control - stop and wait , sliding window protocol, error detection – parity check, CRC, Error control - Stop and wait ARQ, Go back-N ARQ, HDLC protocol, other data link protocols - LAPB, LAPD.
Advanced Encryption Standard, Multiple Encryption and Triple DES, Block Cipher Modes of
operation, Stream Ciphers and RC4, Confidentiality using Symmetric Encryption, Introduction
to Number Theory: Prime Numbers, Fermat’s and Euler’s Theorems, Testing for Primality, The
Chinese Remainder Theorem, Discrete Logarithms, Public-Key Cryptography and RSA
This slide is brief description of DCN of unit-2 .It explains about the different noisy channel and noiseless channel protocols and brief description about HDLC.
About types of errors, Error detection and its types -vertical redundancy check, Longitudinal redundancy check, cyclic redundancy check, checksum, example ,Error correction using Hamming code
1. Kamran Ashraf
MSCs 1st Semester
13-NTU-4009 National Textile University Page 1
Q: What type of errors cannot be detected in all covered
detection algorithms and why? What can be done to detect
such types of errors? Explain above in all one by one error
detection algorithms.
1- Errorsnot detectable by Two Dimensional Parity:
a. Few 4-bit errors are not detectable
b. All 5-bit and above errors are not detectable
Example:
We have Four 7 bit character packet with even parity
Two-Dimensional Parity didn’t detect 4 bit error shown below:
Sent Packet
Even parity
0110100 1
1011010 0
0010110 1
1110101 1
1001011 0
1000110 1
Solution:
Instead of Two dimensional Parity we can use CRC to detect errors upto 32 bit.
2- Errorsnot detectable by the checksum:
a. If somehow two data items gets exchanged during transmission, error is not
detected because sum and the checksum value will remain same.
b. If somehow value of one data item is increased and the value of any other data item
is decreased by the same amount, then the sum and the checksum remain same and
error cannot be detected.
c. If a zero value byte is inserted or deleted, the changes are undetectable.
4-bit Error
not detected
0110100 1
1011010 0
0000111 1
1100100 1
1001011 0
1000110 1
2. Kamran Ashraf
MSCs 1st Semester
13-NTU-4009 National Textile University Page 2
Example:
Four data items got error as the bits got changed but checksum value is same, the error is not
detected by checksum.
Original Data
Data Item
in binary
Checksum
Value
0001 1
0010 2
0011 3
0001 1
Total 7
Solution:
For safe transmission of data more complex algorithms are needed. Cyclic redundancy check
(CRC) is more sophisticated method to detect these kinds of errors.
3- Errorsnot detectable by the Cyclic RedundancyChecks:
CRC can detect broad range for errors however all kind of errors are not detectable.
a. CRC detect burst error upto CRC size only.
b. CRC cannot detect all burst errors that affect an even number of bits.
c. CRC may not detect burst errors of length greater than the degree of the
polynomial.
After undetected Error
Data Item
in binary
Checksum
Value
0011 3
0000 0
0001 1
0011 3
Total 7