Manage End Devices
Parent operation
XBee/XBee-PRO® S2C ZigBee® RF Module
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The parent can buffer one broadcast transmission for all of its end device children. When the parent
receives and buffers abroadcast transmission, it sets a flag in its child table when each child polls and
retrieves the packet. Once all children have received the broadcast packet, the parent discards the
buffered broadcast packet. If all children have not received a buffered broadcast packet and the
parent receives a new broadcast, it discards the old broadcast packet, clears the child table flags, and
buffers the new broadcast packet for the end device children as shown in the following figure.
When an end device sends data to its parent that is destined for a remote device in the network, the
parent buffers the data packet until it can establish a route to the destination. The parent may
perform a route or 16-bit address discovery of its end device children. Once a route is established, the
parent sends the data transmission to the remote device.
End Device poll timeouts
To better support mobile end devices (end devices that can move within a network), parent router
and coordinator devices have a poll timeout for each end device child. If an end device does not send a
poll request to its parent within the poll timeout, the parent removes the end device from its child
table. This allows the child table on a router or coordinator to better accommodate mobile end
devices in the network.
Packet buffer usage
Packet buffer usage on a router or coordinator varies depending on the application. The following
activities can require use of packet buffers for up to several seconds:
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Route and address discoveries
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Application broadcast transmissions
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Stack broadcasts (e.g. ZDO “Device Announce” messages when devices join a network)
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Unicast transmissions buffered until acknowledgment is received from destination or retries
exhausted
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Unicast messages waiting for end device to wake
Applications that use regular broadcasting or that require regular address or route discoveries use up
a significant number of buffers, reducing the buffer availability for managing packets for end device
children. Applications can reduce the number of required application broadcasts, and consider
implementing an external address table or many-to-one and source routing if necessary to improve
routing efficiency.