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Computer Networking : A Top-Down Approach

Computer Networking : A Top-down Approach

Authors:
James F. Kurose, Keith W. Ross
Exercise:
Problems
Chapter:
Transport Layer
Edition:
6
ISBN:
9780132856201
Question:
5

 

Question

Suppose that the UDP receiver computes the Internet checksum for the received UDP segment and finds that it matches the value carried in the checksum field. Can the receiver be absolutely certain that no bit errors have occurred? Explain.

Answer

Certainty of no bit errors at receiver end using checksum using UDP:

 

The receiver in the UDP (User Datagram Protocol) verifies the received segment by calculating internet checksum and comparing it with the value in the checksum field.

  • The 1’s compliment of the sum is considered as checksum. So, when this check sum is used to detect the errors in the packet, the errors remain in under cover.
  • In case, if two 16-bit words are added, then there is a scope for flipping the 0’s and 1’s. If the bits are flipped, the sum will be same and error can’t detected.

 

Therefore, it is not possible to the receiver in UDP to be sure that there are no bit errors have occurred.

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