Lec-8 Cyclic Redundancy Check (CRC) | In detail explanation | Computer Network.
Cyclic Redundancy Check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data. It is based on polynomial division and ensures data integrity by detecting errors during data transmission or storage. Here's a breakdown of how CRC works:
1. Basics of CRC:
Purpose: To detect errors in transmitted or stored data.
Method: CRC appends a checksum (a sequence of bits) to the end of the data to be transmitted. The receiver recalculates the checksum and compares it to the received checksum to verify data integrity.
2. CRC Process:
1. Data Representation:
The data to be sent is represented as a binary string.
A generator polynomial, also in binary form, is predefined and shared between the sender and receiver.
2. Division:
The binary data string is divided by the generator polynomial using binary division. The remainder from this division is the CRC checksum.
3. Appending CRC:
The remainder (CRC checksum) is appended to the original data and sent to the receiver.
4. Verification:
The receiver performs the same division on the received data (original data + CRC). If the remainder is zero, the data is considered error-free.
3. Example:
Data: 1101011011 (binary)
Generator Polynomial: 1011 (binary)
Steps:
1. Append zeroes to the data equal to the length of the generator polynomial minus one: 1101011011000
2. Divide the modified data by the generator polynomial using binary division.
3. The remainder is the CRC checksum, which is then appended to the original data.
4. The receiver repeats the process to check for errors.
4. Properties of CRC:
Error Detection: CRC is effective at detecting burst errors (multiple bit errors in a sequence).
Efficiency: It has low computational overhead and is efficient for hardware and software implementations.
5. Applications:
Networking: Used in protocols like Ethernet, Wi-Fi, and PPP to ensure data integrity.
Storage Devices: Used in hard drives and SSDs to detect data corruption.
File Formats: Employed in formats like PNG and ZIP for error checking.
CRC is a powerful tool for error detection but does not correct the errors; it simply signals their presence, allowing for retransmission or other error-handling mechanisms.