Data communication method based backoff number control

A method for transmitting data in a centralized data communications system using a carrier sense multiplexing access (CSMA) method is provided. The data transmission method uses a backoff number control in a centralized data communications system formed with an access point and stations, the method comprising (a) receiving a multi-poll message containing backoff numbers to be assigned to each station by the access point; (b) setting the backoff numbers of the multi-poll message to the backoff numbers of the stations; and (c) counting down the set backoff numbers and transmitting data. Each station that desires polling registers a station ID and a polling cycle, sets a backoff number contained in a multi-poll message, counts the backoff number, and if the backoff number becomes '0', transmits data such that contention between stations can be prevented. The data transmission method can be applied for controlling media access of a wireless LAN or Home PNA such that time-limited services can be supported. Also, with simple implementation, the method can be easily applied to existing systems such that the method can support real time service in low priced systems.