How Xbee confirm data received from microcontroller via UART?

How Xbee confirm data received from microcontroller via UART?
I send data just from Router to Coordinator and need to know when Xbee router stops communicate with microcontroller and I do software reset by microcontroller.
For example: My atmega every 5 second send mesagge “Hello” and I need to know, what xbee every 5 second answers.
Thanks for help.
Jáchym

It do not acknowledge UART data delivery. You can look at CTS line of module, it will be de-asserted when module’s buffer is about to over-flow.

Other option is to use API mode for communication. In it, when you will receive Ack API frames for your data then will come to know that Tx data not just reached to connected module but is successfully delivered at destination as well.