Protocol for RS485 network?
I have made a demo about transfer TCP/IP through RS485:
https://github.com/dukelec/cdbus_doc

The protocol on RS485 is CDBUS, which could use a standalone controller to solve the collision problem, you can also implement CDBUS protocol by software, or simply don't take care about collision, re-sent packet when data lost was detected.
The CDBUS protocol: https://github.com/dukelec/cdbus_ip

The upon protocol is CDNET, is similar to UDP protocol, you can send UDP packet from MCU by only few line of codes and without any library, but need a gateway to translate CDNET to real TCP/IP protocol.
Or you can define your own protocol, and translate them on the gateway.