This is some information about various protocols used in packet radio.
Keep It Simple Silly
Protocol used between a TNC and a computer. See The KISS TNC: A simple Host-to-TNC communications protocol, and Packet Documents.
AX.25 over IP (Although frequently incorrectly used to mean AX.25 over UDP/IP).
Appears to be an AX.25 frame in an IP packet with the IPPROTO field set to 93.
| IP | AX.25 Frame | AX.25 CRC16 |
AX.25 over UDP/IP
Appears to be an AX.25 frame in a UDP packet. No common port number in usage.
| IP | UDP | AX.25 Frame | AX.25 CRC16 |
There are (at least!) two variants of AXTCP in use. A heuristic for telling them apart is to check the first byte. If it's 0xC0 then it's BPQ (kiss over TCP), otherwise it's xrouter (AXTCP).
Appears to be two byte length (big endian), followed by an AX.25 packet. No common port number in usage.
| IP | TCP | 2 byte len (big endian) | AX.25 Frame | AX.25 CRC16 |
For xrouter at least, the first packet needs to have your alias in the destination field, and your callsign in the source field, the control field can be anything, and the CRC must match.
This is KISS over TCP.