How is the CRC verified?

Introduction

The cyclic redundancy check (CRC) is a type of error-detection method widely used in modern computer networks. It is a checksum procedureIt is a procedure we use to detect errors during data transmission and storage. that we use to identify data inconsistencies, such as bit errors during data transmission. The data is accompanied by a checksum that CRC calculates to help us identify such problems.

Calculation

We carry out the CRC calculation in two steps:

• Generating the CRC on the sender side
• Verifying the CRC on the receiver side

In this answer, we discuss the second one.

Note: To learn how to generate the CRC on the sender side, we can refer here.

Verifying CRC on the receiver side

We send the CRC value, or the remainder, to the receiver with the input data. The receiver has two options for validating the data received:

• It can compute the CRC via binary division, and compare the calculated and received CRC values.
• It can directly append the CRC value to the data. The receiver then calculates the CRC using the entire input. This option is more frequently employed.

If the remainder is $0$, there is no transmission bit error. However, if it is non-zero, there is an error during data transmission. So, the data bits are retransmitted.

Example

Given the $divisor=G=1101$ and $dividend=100010101$ with $CRC=101$, let's verify that the data transmission is error-free.

The following slides depict the detailed verification of the CRC bits.

The remainder here is $0000$. This verifies that data bits are successfully transmitted to the receiver, without any errors.