ARQ
ARQ是Automatic repeat-request的缩写
Automatic Repeat reQuest (ARQ) (or Automatic Repeat-Query) is an error control method for data transmission which uses acknowledgments and timeouts to achieve reliable data transmission over an unreliable service。 An acknowledgment is a message sent by the receiver to the transmitter to indicate that it has correctly received a data frame or packet。 A timeout is a reasonable point in time after the sender sends the frame/packet; if the sender does not receive an acknowledgment before the timeout， it usually re-transmits the frame/packet until it receives an acknowledgment or exceeds a predefined number of re-transmissions。
Types of ARQ protocol include Stop-and-wait ARQ， Go-Back-N ARQ and Selective Repeat ARQ。
