error protection method
During the transmission of digitaldata, disturbances on the transmission paths become noticeable through bit errors. Bit errors can be caused by bad lines, interference pulses, interruptions as well as clock fluctuations. Error protection methods are used to detect bit errors.
InDIN standard 66219, the error protection methods are defined as code-bound and code-unbound methods. Code-bound error protection is performed for longitudinal par ity( LRC) with the aid of parity bits( PY) and for transverse parity ( VRC) with block check characters( BCC), whereby even parity is specified for asynchronous transmission and odd parity for synchronous transmission. Furthermore, the following procedures are used in connection with the block check characters or error protection: Cyclic Redundancy Checksum(CRC); Block Check Character (BCC); Frame Check Sequence( FCS).
IBM used either the cross parity (VRC) and longitudinal parity (LRC) procedures or the cyclic block check (CRC) for the BSC procedure. For the bit-oriented procedures such as the SDLC protocol and the HDLC protocol, the generator polynomial CCITT-16, as described in the DIN standard, is used uniformly.