How to organize the most simple in terms of code, two-way communication between five arduino?

Question

Arduino

It is necessary to connect 5 arduino modules, one of them is a master, the rest are slaves. What protocol and hardware is better to use to conduct parallel data transfer. There won’t be much data coming in, but they should go in both directions, and it’s important to find a solution in which I don’t have to train each module to track if other modules are talking to the network now.
Those. I ask you to advise the most simple library, and iron, so that it can penetrate 30 meters and a convenient, easy-to-learn communication protocol is organized.
There is almost no experience in exchanging data between arduinos.

Answer 1

Should communication be by wire or by radio? If by wire, then MODBUS over RS-485.
hardware: https://www.sparkfun.com/products/12965
software: www.freemodbus.org

Answer 2

watch this

Answer 3

Arduino does not have 5 ports to be able to receive data in parallel without loss. But you can connect a CPLD to it by implementing these 5 ports in it, connecting it with Arduino via SPI.