how to transmit change in rssi from coordinator to router?

hi I am working on a project related to measuring RSSI.In this project I am using 2 xbees s1 and 2 arduino . In my project all I have to do is to measure rssi between two xbees and then finding the change in rssi and finally transmit this change to other xbee . i have tried many times but i can’t get help regarding transmission of change in rssi . plz anyone help me