# AX.25

AI-generated

The link-layer protocol of packet radio:
[HDLC](../hdlc/index.html.md) frames addressed by callsign and SSID,
with an optional path of [digipeaters](../digipeater/index.html.md).
It has connectionless (UI) frames, which [APRS](../aprs/index.html.md) uses,
and a connected mode with acknowledgements and retries.
[FX.25](../fx25/index.html.md) and [IL2P](../il2p/index.html.md) add forward error correction on air.

## References

* [AX.25 Link Access Protocol for Amateur Packet Radio, v2.2](https://www.tapr.org/pdf/AX25.2.2.pdf) (TAPR)
* [AX.25 on Wikipedia](https://en.wikipedia.org/wiki/AX.25)