A method and system for transmitting digital data by extending the sequence numbering range for a selective repeat transmission protocol are described. In accordance with one embodiment of the invention, data frames (70) are transmitted including an eight-bit sequence number (72) and a one-bit retransmit flag (74). The one-bit retransmit flag (74) indicates whether the frame is newly transmitted or retransmitted due to a failed first transmission. Transmit (50) and receive (52) systems each maintain a twelve-bit sequence number referred to as a 'long sequence number' comprised of the eight-bit sequence number transmitted with each frame and a four-bit extension. The long sequence number is transmitted within a control frame (82) and the eight-bit sequence number is transmitted within the data frame (72).