The 64kbit/s transmission by the 'guaranteed' transmission formula was originally released in the standardized PIAFS version 2. In this transmission formula, two sets of 32kbit/s data slots were required throughout the transmission in order to carry out a 64kbit/s data transmission. If either of the two slots were unavailable, the 64kbit/s data transmission access was often interrupted.
In the newly released 'best effort' transmission formula, data transmission will continue at 64kbit/s if two slots are available and automatically shift down to 32kbit/s whenever one of the data slots becomes unavailable. This formula will enhance the convenience to those using the 64kbit/s data transmission service.

This standardization is applied to the transmissions between the PS (Personal Station) and the TAP (Terminal Access Point). PIAF is currently working on the standardization of the 'best effort' transmission formula protocol for the transmission between PSs as well.