How to know if XBee Router node is disconnected to Coordinator

Hello guys. For some time I've been able to use my XBee modules successfully by being able to transmit packets between the coordinator and routers.

However, I would want to take it further by being able to know whether or not my nodes are still connected to the coordinator.

How do I do this by using Andrew Rapp's XBee library? I use Arduinos by the way and XBee Series 2 modules.

Also, I'm following the examples from Matthijs Koojiman's book, Building Wireless Sensor Networks using Arduino. I modified the codes heavily and already got them working for my fire and panic alarm project.

Thank you! If you guys need the code, please do tell me. It's very long.