Automatic repeat request
Automatic repeat request (ARQ), also known as automatic repeat query, is an error-control method for data transmission that uses acknowledgements (messages sent by the receiver indicating that it has correctly received a message) and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received). If the sender does not receive an acknowledgment before the timeout, it re-transmits the message until it receives an acknowledgment or exceeds a predefined number of retransmissions.