Error correction mode

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Error Correction Mode ( ECM ; German  error correction mode ) is an additional feature of the group 3 fax machines.

In order to be able to use this additional feature, fax machines require a document memory. Using ECM, the document is divided into a maximum of 256 segments, each with 256 bytes. These segments are called frames. Each of these frames is provided with a checksum. These frames with checksum are then transmitted to the recipient. The recipient saves the received frames in the document memory and checks the checksum. If the checksum of one or more frames does not match the checksum, the receiving machine only requests the incorrect frames from the sender again. If the previously defective frame is received without errors when it is retransmitted, the defective frame is deleted from the document memory and replaced with the error-free frame. After all frames have been received and tested with the checksum, the document is sent to the printer of the fax machine and printed.

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Each fax machine can be set to a certain level of fault tolerance; this value is usually around 10–15%, which means that documents with defective frames can also be printed if a multiple transmission of the defective frames fails. Whether the entire transmission is rated as faulty or faultless depends on the recipient and its fault tolerance settings. These settings sometimes mean that some lines do not appear or appear difficult to read.
In the era of VoIP (Voice over IP) or FoIP (Fax over IP), activated ECM can cause problems.

ECM in theory

ECM in theory

literature

  • Markus Aigner: The fax manual. Technology, tips and trends . Debis Advanced Communication Services GmbH, Düsseldorf 1995, ISBN 3-00-000017-8 .
  • Konica Minolta: Training Academy “M + Fax Basics” .