Specifications
XBee®/XBee‐PRO®SERFModules
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BroadcastDataTransmission
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.
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 the "RF Packet Routing" section in chapter 4 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.
When sending a unicast transmission, the ZigBee network layer uses the 16-bit address of the
destination and each hop to route the data packet. If the 16-bit address of the destination is not
known, the ZigBee stack includes a discovery provision to automatically discover the destination
device's 16-bit address before routing the data.
To discover a 16-bit address of a remote, the device initiating the discovery sends a broadcast
address discovery transmission. The address discovery broadcast includes the 64-bit address of
the remote device whose 16-bit address is being requested. All nodes that receive this
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Legend
C=Coordinator
R=Router
E=End Device
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