APRS
The Automatic Packet Reporting System: positions, messages, objects, weather and telemetry sent as AX.25 UI frames, spread by digipeaters and gatewayed to the internet (APRS-IS) by IGates.
References
The APRS Documentation Project - collected specifications, including
APRS101.pdf,Understanding-APRS-Packets.pdfandAPRS-Digipeater-Algorithm.pdf