Broadcast transmissions

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 retransmits 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). For more information, see Parent operation.

Each node that transmits the broadcast also creates an entry in a local broadcast transmission table. This entry keeps track of each received broadcast packet to ensure the packets are not transmitted endlessly. Each entry persists for 8 seconds, and the broadcast transmission table holds 8 entries, effectively limiting network broadcast transmissions to once per second.

For each broadcast transmission, the Zigbee stack reserves buffer space for a copy of the data packet that retransmits the packet as needed. Large broadcast packets require more buffer space. Users cannot change any buffer spacing; information on buffer space is for general knowledge only. The XBee 3 Zigbee RF Module handles buffer spacing automatically.

Note Broadcast transmissions do not use ACKs, so there is no guarantee that every node will hear a particular broadcast. Because the XBee devices re-transmit broadcast transmissions by every device in the network, use broadcast messages sparingly.