How does forward error correction (FEC) allow the receiver to correct data errors?

Forward Error Correction (FEC) is a technique used in digital communications to improve reliability. It works by having the transmitter add redundant data—essentially mathematical extra bits—to the original message before it is sent. When the receiver processes the incoming signal, it uses this redundant information to detect and mathematically reconstruct any bits that were corrupted by noise or interference during transmission. This happens "forward" without needing to ask the transmitter to resend the data. Other options like parity bits can only detect errors but not correct them on their own, while Varicode is simply a variable-length character encoding system, not an error correction method.