AX.25

• OSI layer 2 (data link layer) protocol. Technically, it occupies layers 1-3.
• Same layer as BATMAN-Advanced.
• Used for packet radio by hams.
• Can transport network layer protocols, including IP.
• Not designed to support switching, though routers can probably be set up to handle it.
• Support in the Linux kernel.
  • v2.6.x: ax25.ko
• Commonly used with three different communication specs:
  • Bell 103 tones @ 300bps
  • Bell 202 tones @ 1200bps
  • G3RUH DFSK @ 9600bps
  • These speeds are hard limits.
• KISS encapsulates frames such that they can be send to a TNC for transmission. Derived from SLIP.
• KISS is a serial protocol. Thus, multiple serial channels are required for multiple transceivers.
• Other protocols fulfill the same function.
• Either half or full duplex modes.
• Three components
  • Kernel module
  • Configuration utilities
  • Utility software
• Each AX.25 network device ("port") must be configured with a unique callsign/SSID. Hostnames are probably not a good idea.
• We would be using soundmodem on top of AX.25.

Configuring AX.25 network interface:

 ifconfig sm0 hw ax25 <callsign> up

 Create an entry in /etc/ax25/axports for the network interface:
     sm0 <callsign> <speed in bps> <maximum packet length> <AX.25 window parameter (K)> <description of interface>

Once this is done, you can treat it like any other network interface:

 ifconfig sm0 192.168.1.1 netmask 255.255.255.0
 route add -net 192.168.1.0 netmask 255.255.255.0 sm0
 route add default sm0

Using /usr/bin/call to test an AX.25 connection.

Wikipedia: AX.25 About AX.25 Linux AX.25 Howto