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crc

Where does the CRC part come from?

Consider the following exam question:

Use the CRC polynomial generator x2 + 1 to find out if the following received message contains any errors : 10111111. Show the exact user data received separate from the actual CRC.

The Provided Answer:

Generator Binary: 101

Two Zeros are appended to the message.

101 / 10111111 => Remainder = 01

Original Message= 101111 CRC = 11

I am trying to figure out how the CRC part of 11 is derived.

Thanks in advance.

Solution

  • All it's saying is simply that the message 10111111 consists of the content 101111 and the CRC 11. The CRC of the content is appended to the content to make up the message. If the message is received correctly, then dividing the entire message by the CRC polynomial should result in a remainder of zero. I.e. the CRC of the content plus a correct CRC is necessarily zero.

    Since the remainder was 01, the message must be in error.