AX.25 v2.2 (1998) added improvements to improve efficiency, especially at higher data rates. Stations can automatically negotiate payload sizes larger than the previous limitation of 256 bytes. Extended sequence numbers (7 vs. 3 bits) allow a larger window size, the number of frames that can be sent before waiting for acknowledgement. "Selective Reject" allows only the missing frames to be resent, rather than having to wastefully resend frames that have already been received successfully. Despite all these advantages, few implementations have been updated to include these improvements published more than 20 years ago. The only known complete implementation of v2.2, at this time (2020), is the Dire Wolf software TNC.