Error Detection

In communications, error detection refers to a class of techniques for detecting garbled messages. Two of the simplest and most common techniques are called checksum and CRC. More sophisticated strategies include MNP and CCITT V.42 .

Error detection and correction add some redundency (i.e. some extra data) to a message, which receivers can use to check consistency of the delivered message, and to recover data determined to be erroneous.

A common method of error detection Automatic Repeat reQuest (ARQ) is an error control method for data transmission that makes use of error-detection codes, acknowledgment and/or negative acknowledgment messages, and timeouts to achieve reliable data transmission. An acknowledgment is a message sent by the receiver to indicate that it has correctly received a data frame.
Usually, when the transmitter does not receive the acknowledgment before the timeout occurs (i.e., within a reasonable amount of time after sending the data frame), it retransmits the frame until it is either correctly received or the error persists beyond a predetermined number of retransmissions.