Digi International Inc XBEEPRO2 User Manual

Broadcast transmissions within the ZigBee protocol are intended to be propagated throughout the entire 
network such that all nodes receive the transmission. To accomplish this, the coordinator and all routers that 
receive a broadcast transmission will retransmit the packet three times. 

Note: when a router or coordinator delivers a broadcast transmission to an end device child, the transmission is 
only sent once (immediately after the end device wakes and polls the parent for any new data). See Parent 
Operation section in chapter 6 for details.

Each node that transmits the broadcast will also create an entry in a local broadcast transmission table. This 
entry is used to keep track of each received broadcast packet to ensure the packets are not endlessly 
transmitted. Each entry persists for 8 seconds. The broadcast transmission table holds 8 entries.

For each broadcast transmission, the ZigBee stack must reserve buffer space for a copy of the data packet. This 
copy is used to retransmit the packet as needed. Large broadcast packets will require more buffer space. This 
information on buffer space is provided for general knowledge; the user does not and cannot change any buffer 
spacing. Buffer spacing is handled automatically by the XBee module.

Since broadcast transmissions are retransmitted by each device in the network, broadcast messages should be 
used sparingly.

Unicast transmissions are sent from one source device to another destination device. The destination device 
could be an immediate neighbor of the source, or it could be several hops away. Unicast transmissions that are 
sent along a multiple hop path require some means of establishing a route to the destination device. See the 
"RF Packet Routing" section in chapter 4 for details.

As mentioned previously, each device in a ZigBee network has both a 16-bit (network) address and a 64-bit 
(extended) address. The 64-bit address is unique and assigned to the device during manufacturing, and the