xBee nodes and coordinator busy

Hello, could someone explain me what happen if an xBee node try to speaks with the coordinator (or a router) that is busy because is already receiving (or sending) messages with someone else? Is it possible in API mode to set the radio to retry till the coordinator is free?
Thanks

The XBees have error handling built in. When an XBee sends data, and receipt is not acknowledged, it sends it again, until it is. So, I think that your situation is covered.

If a node tries to send, but the coordinator does not acknowledge receipt of the packet (because it was busy) the end node should try to send again (and again). The number of retries is configurable, if I remember correctly.

I don't think that API mode makes any difference.

I have contacted digi for knowing how to set the number of retries, unfortunatly they give me this answer:

"In a very basic level, if a device attempts to talk to another device that is already receiving data, the device transmitting will not receive the required MAC level ACK. When this ACK is not received a back-off and re-transmission or Retry will occur. No, you do not have the ability to set the number of retries that occurs. This is determined by the MAC layers designated within the IEEE 802.15.4 specifications."

I think the only way is to implement control on an higher level, on the arduino code. The problem is that in a wirless sensor network a microcontroller is not always included in the sensor node. So on a stand alone end node i cannot set retries values at all :(