Tanenbaum Networks

Question

A 1024-bit message is sent that contains 992 data bits and 32 CRC bits. CRC is com- puted using the IEEE 802 standardized, 32-degree CRC polynomial. For each of the following, explain whether the errors during message transmission will be detected by the receiver:

(a) There was a single-bit error.

(b) There were two isolated bit errors.

(c) There were 18 isolated bit errors.

(d) There were 47 isolated bit errors.

(e) There was a 24-bit long burst error.

(f) There was a 35-bit long burst error.

 

In the above question can anyone explain for option (c).

Answer 1

18 bits error are not detected by CRC 32 because it is even bit error.

Comments

You are correct when the 18 bits are continuous. But they said 18 isolated bit errors. Also I would like some detailed explanation for each scenario.

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What is the difference in c and e option?

Answer 2

1. a.

   , Cyclic Redundancy Check (CRC) checksum detects all single bit errors during the data transmission of 1024 bit.

   • Single bit errors is detected by CRC method.

   o It produces 100 percentage of error detection.

2. Step 3 of 7

   b.

   , Cyclic Redundancy Check (CRC) checksum detects all double bit errors during the data transmission of 1024 bit. That is, two isolated error bits for long messages.

   • Double bit errors are detected by CRC method.

   o It produces 100 percentage of error detection and creates the generating polynomial for at least three 1s.

3. Step 4 of 7

   c.

   , Cyclic Redundancy Check (CRC) checksum does not detect all even bit errors during the data transmission of 1024 bit. That is, 18 bits of isolated errors for long messages.

   • Even number of bits in error is not detected by CRC method.

   o It produces the near of 100 percentage of error detection.

4. Step 5 of 7

   d.

   , Cyclic Redundancy Check (CRC) checksum detects all odd bit errors during the data transmission of 1024 bit. That is, 47 bit of isolated errors for long messages.

   • Odd number of bits in error is detected by CRC method.

   o It produces the 100 percentage of error detection and also creates the generating polynomial for x + 1 factor.

5. Step 6 of 7

   e.

   , Cyclic Redundancy Check (CRC) checksum detects all burst errors with the burst length of less than or equal to 32 degree during the data transmission of 1024 bit.

   • Length of error burst is less than r+1 (“r” represents the degree of generating polynomial) is detected by CRC method.

   o It produces the 100 percentage of error detection.

6. Step 7 of 7

   f.

   , Cyclic Redundancy Check (CRC) checksum does not detect burst errors of burst length greater than 32 degree during the data transmission of 1024 bit.

   • Length of error burst is greater than or equal to r bits (“r” represents the degree of generating polynomial) is not detected by the CRC method.