End Device Poll Timeouts; End Device Child Table; Packet Buffer Usage - Digi XBee 3 ZigBee User Manual

Manage End Devices
The parent can buffer one broadcast transmission for all of its end device children. When the parent
receives and buffers a broadcast 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.

End Device child table

The child table timeout is controlled by setting the
Device sends the child table timeout value to the parent when joining a network. The ET setting
should be a value greater than the expected End Device sleep time—see
child table timeout values.

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:
Route and address discoveries
n
Application broadcast transmissions
n
Stack broadcasts (for example ZDO "Device Announce" messages when devices join a network)
n
Unicast transmissions buffered until acknowledgment is received from destination or retries
n
exhausted
Unicast messages waiting for end device to wake
n
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
Digi XBee® 3 Zigbee® RF Module
ET (End Device Timeout) on the End Device. The End
ET (End Device Timeout)
Parent operation
for
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