FX.25 provides a Forward Error Correction (FEC) capability while maintaining legacy compatibility with non-FEC equipment.
FX.25 was created by the Stensat Group in 2005, and was presented as a technical paper at the 2006 TAPR Digital Communications Conference in Tucson, AZ.
The Preamble and Postamble blocks are variable length, and are included to account for delays typically found in radio links - transmitter "key" to stable operation, receiver squelch latency, etc.
The FEC frame currently implements Reed Solomon error correction algorithms, but is not restricted to these.
Performance improvement will be a function of AX.25 packet size combined with the noise characteristics of the transmission channel.