I use serial, 232 and 485 to send messages between devices. The are simple Ascii strings. I need to send these message by ethernet as well. What is the simplest way to do this ?
Do you mean IP? IP can go over Ethernet(wire) or WiFi(Wireless).
If you want a reliable connection, use TCP/IP and not UDP to send your messages. With TCP/IP you make a connection from client to server and once connected, you can send data back and forth over the connection. If there is no device on the other end, the connection fails so you can know if the device is active or not.
It does require you to know the IP address of each device on the network and for the IP address to remain constant via static setup or dynamic using the router to always allocate an IP based on the MAC address.
You can send binary or ASCII with TCP.
What type of system are you looking to use this for?