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Transmission, addressing, and routing Data transmission

XBee/XBee-PRO ZigBee RF Modules User Guide 55

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 on page 89 for details.

Broadcast data transmission

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 eight seconds. The broadcast transmission table holds eight 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

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 RF

packet routing on page 60 for details.

Address resolution

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 16-bit

address is obtained after joining a network. The 16-bit address can also change under certain conditions.

Legend

C=Coordinator

R=Router

E=End D evice

Digi XBEE2 User Manual

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