Cyclic Redundancy Check (CRC) - Part 2

Summary

In this session, the focus is on how the receiver detects transmission errors using the Cyclic Redundancy Check (CRC) technique. Building on the previous lecture's example, the process of error detection is explained through polynomial long division, with a detailed walk-through of how the receiver checks for errors by dividing the received data with a common divisor. If the remainder is zero, the data is considered error-free. The session also covers a practical example where deliberate corruption of data triggers an error detection, demonstrating the effectiveness of CRC in error handling and ensuring data integrity.

Takeaways

• 😀 In Part 1, we learned how the sender creates a CRC to detect errors in data transmission.
• 😀 In Part 2, the focus is on how the receiver uses the CRC to detect errors in the transmitted message.
• 😀 The receiver uses the same polynomial divisor as the sender to verify the transmitted data.
• 😀 If the remainder of the division performed by the receiver is zero, it indicates no transmission errors.
• 😀 A non-zero remainder during the division means that an error occurred during transmission.
• 😀 In the previous example, the receiver performed polynomial long division on the received message and found that the remainder was zero, indicating no errors.
• 😀 The divisor used in CRC is a polynomial expression that is agreed upon by both the sender and the receiver.
• 😀 If the message is received without transmission errors, the receiver will accept the data as valid.
• 😀 Deliberate error introduction (such as flipping a bit) will result in a non-zero remainder when the receiver performs the division, signaling a transmission error.
• 😀 An interactive exercise was given where students practice CRC error detection by simulating a transmission error and performing polynomial division.
• 😀 The CRC technique ensures data integrity by allowing the receiver to detect errors in a reliable and efficient manner.

Q & A

What is the main focus of part two of the CRC lecture?

The main focus of part two of the CRC lecture is explaining how the receiver detects errors using the Cyclic Redundancy Check (CRC) technique.

What data was transmitted in the example used in the previous lecture?

In the previous lecture, the transmitted data was '1 0 0 1 0 0 0 1', where '1 0 0 1 0 0' was the actual data, and '0 0 1' was the CRC.

How does the receiver detect if the transmitted message is error-free?

The receiver performs the same polynomial division on the received message, using the same divisor. If the remainder of the division is zero, the receiver concludes that there are no errors in the transmission.

What role does the divisor play in error detection in CRC?

The divisor, which is a polynomial expression, is used by both the sender and the receiver. It is essential for performing the polynomial division to detect errors in the transmission.

What would the receiver do if the remainder is non-zero after performing the division?

If the remainder is non-zero after the receiver performs the polynomial division, it indicates that there is an error in the transmission.

In the example, what does it mean if the remainder after polynomial division is zero?

If the remainder is zero, it means there were no transmission errors, and the receiver accepts the transmitted data as correct.

What is the CRC technique used for in data transmission?

The CRC technique is used to detect errors in data transmission by generating a CRC value that is appended to the data. The receiver checks for errors by performing polynomial division.

How is error detection performed if a transmission error occurs?

If a transmission error occurs, the receiver will perform polynomial division on the received message, and the remainder will not be zero, indicating the presence of an error.

What is the homework problem in the lecture about?

The homework problem involves transmitting a message '1 1 0 0 1 0 0 1' and using the CRC polynomial to protect it from errors. After deliberately corrupting a bit, the receiver will detect the error by performing polynomial division, which will yield a non-zero remainder.

What happens when the leftmost third bit of the transmitted message is corrupted?

When the leftmost third bit of the transmitted message is corrupted, the receiver will detect the error because the polynomial division will result in a non-zero remainder, signaling an error in transmission.