In ARQ, each character is transmitted twice, with the second displaced in time from the first.

In ARQ, the "sending" station transmits a block of three characters and the "receiving" station responds with a one character Repeat Request. Following this the "transmitting" station will send a new block.

In ARQ, the ISS transmits a block of 3 characters and the IRS checks for parity . If the received block is correct a one-character control signal is sent notifying the ISS to proceed with the next block. If the parity check fails the block must be resent .

Broadcasts of Maritime Safety Information, traffic lists, etc. can be copied by the receiving station in ARQ mode.