Spell,
I think you also need to download and look at the 802.15.4 specification.
the 802.15.4 have an addressing scheme with build in acknowlegde.
What you are attempting to do will require a "network" layer on top.
That is why I suggested that reading the ZigBee specification would give you some ideas on this.
You dont have to implement mesh routing to get tree routing - but you need to implement it your self.
else I can recommend that you look at the SMAC, which today have an repeater application that allows you to extend a network.
BR,
Mads