Now I would measure the reliability of my communication, and one of the parameters I would measure is the loss packet rate. To do it, I realize that the isError function is not properly what I want, because doesn't analyze actually the if the received packet is good. You can read the description of this function:

public boolean isError()

Indicates an error occurred during the parsing of the packet. This may indicate a bug in this software or in the XBee firmware. Absence of an error does not indicate the request was successful; you will need to inspect the status byte of the response object (if available) to determine success.

Do you have any idea to implement what I want to do?

Thanks!