Error Checking Basics

Error-checking schemes determine whether transmitted data has become corrupt or otherwise damaged while traveling from the source to the destination. Error checking is implemented at several of the OSI layers.

One common error-checking scheme is the cyclic redundancy check (CRC), which detects and discards corrn pted data. Error-correction functions (such as data retransmission) art left to hightr-laytr protocols. A CRC value is generated by a calculation that is performed at the source device. The destination device compares this value to its own calculation to determine whttht-trrors occurred during transmission. First, the source device performs a predetermined set of calculations ovtp the contents of the packet to be sent. Then, the source places the calculated value i d the packet and sends the packet to the destination. The destination performs the same predtttrmi ntd set of calculations over the contents of the packet and then comparts its computed value with that contained in the packet. If the values art equal, the packet is considered valid. If the values art unequal, the packet contains errors and is discarded.

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