9600 bps Packet Radio only twice as fast as 1200

AX25 V2.2

Most AX.25 connected mode implementations were written in the previous Century and are based on the standard from 1984.  They were not updated when the protocol was enhanced in 1998.

The newer version has several improvements that make bulk transfer of data more efficient.

  • Larger packets.
  • Larger window size.  (number of information frames that can be sent before waiting for an ack.)
  • More efficient acknowledgements.
  • Much more efficient retransmission for lost packets.
  • Completely interoperable with the v2.0 standard.

I also make the case that using a KISS TNC for connected mode packet is greatly lacking because the connection oriented protocol does not know about the radio status or the transmit queue length in the TNC.

More in-depth description can be found here:
https://raw.githubusercontent.com/wb2osz/direwolf/dev/doc/Why-is-9600-only-twice-as-fast-as-1200.pdf

1 thought on “9600 bps Packet Radio only twice as fast as 1200”

  1. A larger packet size and a larger window size only plays well if the bit error rate is very low. Even with forward error correction, it would be better for us to have a smaller block committed to transmit before getting an acknowledgment. My new plan uses 64-byte packets in a set of 12 before unkeying to get an acknowledgment.

    A much better experiment would be to do the windowsize of 1 with 256 byte packet vs the larger packet and larger windowsize on a decently long link channel. Try it on 2m at 20 miles.

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