Block check string

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The term block check sequence  (BPF) ( English Frame Check Sequence  (FCS) ) denotes a checksum that is added to a data block ( frame ) of a network protocol in order to enable error detection (also error correction on layer 2, see below). It is often a Cyclic Redundancy Check  (CRC) ( German  Cyclic Redundancy Check ) used with 32-bit z. B. in Ethernet and other IEEE 802 protocols. There are also 8 bit, 12 bit and 16 bit variants.

Error detection and correction procedures based on an FCS are to be assigned to the data link layer (Layer 2 / Layer 2) of the OSI model .

The sender calculates the checksum for the entire data block and appends it to the end of the block. The receiver also calculates the checksum of the block and compares it with the FCS sent. The same algorithm is used for the calculation on both sides . If the check fails, the block will be discarded by the recipient.

In the case of the block check character sequence, transmission starts with the most significant bit ( MSB ).

An Ethernet frame with the FCS at the end

See also

literature

  • Hans-Jochen Schneider: Lexicon computer science and data processing . 4th edition, R. Oldenbourg Verlag, Munich 1998, ISBN 3-486-24538-4 .
  • Eckart Giese, Klaus Görgen, Elfriede Hinsch, Günter Schulze, Klaus Truöl: Services and protocols in communication systems . Springer Verlag, Berlin / Heidelberg 1985, ISBN 978-3-642-70440-6 .
  • Harald Schumny, Rainer Ohl: Handbook of digital interfaces . Friedrich Vieweg & Sohn Verlagsgesellschaft, Braunschweig 1994, ISBN 978-3-528-04911-9 .
  • Harald Schumny: Signal transmission . 2nd revised edition, Friedrich Vieweg & Sohn Verlag, Braunschweig 1987, ISBN 978-3-528-14072-4 .
  • Peter R. Gerke: New Communication Networks . Springer Verlag, Berlin / Heidelberg 1982, ISBN 978-3-642-93207-6 .

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