NPR (New Packet Radio) is a custom radio protocol, designed to transport bidirectional IP trafic over 430MHz radio links (ham radio). This protocol is optimized for "point to multipoint" topology, with the help of managed-TDMA.
Bitrate is up to 500kbps (net, effective bitrate).
The radio modem is cheap (~80$) and home-made, with a 433MHz ISM module inside. The modem is connected locally with Ethernet, therefore no specific software is needed on PC.
The modem is easy to build and reproduce.
You can add a DMR radio amplifier in order to achieve 20W radio power or more.
The main usage is an extension of HSMM - Hamnet networks.
All the project is open-source : hardware, software, protocol specification.
If you have questions, you can use the public chat room, or contact me via e-mail : f4hdk[at]free[dot]fr