11. Automatic Repeat Request#

  • Automatic Repeat Request (ARQ) is the generic term for a class of error control strategies employed in the data-link control (DLC) layer.

  • Typically, ARQ implies retransmission of erroneous packets in the DLC layer. In order to do so, ARQ requires the following two basic capabilities of the underlying communication system:

    1. The ability to detect transmission errors in the received packets.

    2. The availability of a feedback channel from the TX back to the RX to signal the need of retransmission.

  • We will introduce a common class of error detecting codes, called the cyclic redundancy check (CRC) codes, to perform error detection.

  • We will also present a few simple ARQ protocols to guarantee successful transmission of packets in the DLC layer from communication node to another.