How Zigbee works:
Direct Sequence Spread Spectrum: Allows for multiple transmissions to share the same frequency range. Add a pseudonoise sequence to your signal, then subtract it at the receiving end. Your signal gets amplified, and all other signals get no gain.

Ad-Hoc On-demand Distance Vector: Establishes routes between nodes when needed. A node that needs a connection broadcasts its need. Other nodes forward the request. The route with the least hops is chosen and used.

CSMA/CA: Can't use collision detection with wireless because you can't transmit and receive at the same time. When a node wishes to transmit, it listens for a while to see if the channel is busy.

Unicast: A packet with just one target address.
Multicast: A packet with a range of target addresses.
Broadcast: A packet meant to absolutely be received by everyone. Each node that receives a broadcast packet makes sure to rebroadcast the packet three times. Broadcast packets are not good for general data, because the broadcast buffer is only of size 8, and broadcasts persist for 8 seconds.