Due to the high compression factors used in MPEG decoding of digital signals, Error Correction Modes become necessary, to avoid any significant loss of bit information during signal transmission. Commonly applied are Reed-Solomon Codes. The efficiency of error correction models are defined by the so called bit error rate (BER), which gives the quotient received bits to the total number of transmitted bits in a specific time period.
When ECM is utilized, a receiving fax machine will check data for errors before printing the document. If errors are found, it will signal the transmitting machine to re-send the information. Both communicating units must support this mode for it to be utilized.
Error correction mode (ECM) is an optional transmission mode built into Class 1 fax machines or fax modems. ECM automatically detects and corrects errors in the fax transmission process that are sometimes caused by telephone line noise. The page data is divided into what is known as Octets (small blocks of data).