1. One class of weak d ata integrity mechanisms (which we did not discuss in any
ID: 3904993 • Letter: 1
Question
1. One class of weak d ata integrity mechanisms (which we did not discuss in any detail) can only detect accidental modification of data. (a) A single parity check bit consists of the XOR of all the bits in the data. What types of accidental errors will this simple integrity mechanism detect? (b) In what ways are cyclic redundancy checks (CRCs) better data integrity mechanisms than parity check bits? (c) Explain why a CRC is not a strong data integrity mechanism. (d) Identify two different applications which use CRCs to provide data integrity. and explain why they do not need a stronger data integrity mechanism.Explanation / Answer
a) A single parity check using XOR of all the bits will only check if any single bit of the data got modified accidentally during the transmission. It will not be able to detect if burst errors have occurred. Say for a data 1 got accidentally changed to 0 it can detect very easily but if multiple bits gets changed simultaneoulsy, then this Single Parity check will fail in detecting the errors.
b) A cyclic code has favorable properties that make it well suited for detecting burst errors. CRCs are particularly easy to implement in hardware, and are therefore commonly used in digital networks. as compared to Single Parity check, it can only detect changes in a single bit and cannot detect multi bit errors. So, in such a case of burst error CRC is more advantageous to Parity Bit checks.
c) A cyclic redundancy check (CRC) is a non-secure hash function designed to detect accidental changes to digital data in computer networks; as a result, it is not suitable for detecting maliciously introduced errors. Because its not secure anyone can intercept the network and change the original Hash Function thus resulting in failure of CRC. This way CRC becomes weak in Data integrity mechanisms.
d) 1. The application of CRC in the radio frequency identification protocol ISO15693 is analyzed. Based on CRC, the multiple bits error correction function is realized in the decode process of Manchester Code. The selection of decision threshold and error correction bits is analyzed. The simulation and application results prove the validity of the multiple bits error correction algorithm. Hence CRC works best for Radio Frequency Identifications Protocol
2. IBM's Synchronous Data Link Control use CRC-16, another 16-bit polynomial. A 16-bit cyclic redundancy code detects all single and double-bit errors and ensures detection of 99.998% of all possible errors. This level of detection assurance is considered sufficient for data transmission blocks of 4 kilobytes or less. For larger transmissions, a 32-bit CRC is used.
Please let me know in case of any clarifications required. Thanks!
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