hopes that at least one copy of the message gets through. The acknowledgement function is used in the automatic repeat request (ARQ) function. Acknowledgement frames are numbered in coordination with the frames that have been received and then sent to the transmitter. This allows the transmitter to avoid overflow or underrun at the receiver, and to become aware of any missed frames. In Binary Synchronous Communications, the NAK is used to indicate that a transmission error was detected in the previously received block and that the receiver is ready to accept retransmission of that block. Bisync does not use a single ACK character but has two control sequences for alternate even/odd block acknowledgement. Hardware acknowledgment Some computer buses have a dedicated acknowledge wire in the control bus used to acknowledge bus operations: DACK used for ISA DMA; DATACK used in the STEbus, the data transfer acknowledge pin of the Motorola 68000 that inspired the title of DTACK Grounded, etc. Some computer buses do not always acknowledge every write; some or all of the writes use a posted write. The I²C serial bus has a time slot for an acknowledgment bit after each byte. See also C0 and C1 control codes Flow control (data) NACK-Oriented Reliable Multicast References External links Control characters Data transmission Error detection and correction Flow control (data) Link protocols Network protocols Routing protocols