In a data communication system which reduces traffic on a wireless network by reducing Ack responses, on a transmitting side, an Ack request provided within a wireless data frame is validated (turned “ON”) to be transmitted; and an Ack request cycle is extended when an Ack in response to the Ack request has been received within a fixed time (timeout period “To”) during a cycle for transmitting the Ack request while if otherwise, the cycle is shortened. On a receiving side, only in case that a frame identifier indicating a sequence of an Ack request is found to be an expected one and the present Ack request receiving interval is found to be longer than the last Ack request receiving interval, a redundant transmission frequency of the Ack in response to the Ack request is decreased while the Ack request receiving interval is updated to the present interval in either case.