- 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](Notes_on_Soundmodem "wikilink") 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.](http://tldp.org/HOWTO/AX25-HOWTO/x1449.html)

[Wikipedia: AX.25](https://secure.wikimedia.org/wikipedia/en/wiki/AX.25)
[About AX.25](http://www.tapr.org/pub_ax25.html) [Linux AX.25
Howto](http://tldp.org/HOWTO/AX25-HOWTO/)

[Category:Byzantium](Category:Byzantium "wikilink")