Sleep modes Sleeping routers
XBee® SX 868 RF Module User Guide
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Indirect messaging only functions with P2MP unicast messages. Indirect messaging has no effect on
P2MP broadcasts, directed broadcasts, repeater packets, or DigiMesh packets. These messages are
sent immediately when received over the serial port and are not put on the indirect messaging queue.
Polling
Polling is the automatic process by which a node can request data from an indirect messaging
coordinator. To enable polling on a device, configure it as an end device with the CE command. When
you enable polling, the device sends a poll request a minimum of once every polling interval, where
the polling interval is 100 ms for the 80 Kb/s data rate and it is 300 ms for the 10 Kb/s data rate. When
the device sends normal data to the destination specified by the DH/DL of end device module, the
data also functions as a poll.
When a polling device is also an asynchronous sleeping device, that device sends a poll shortly after
waking from sleep. After that first poll is sent, the device sends polls in the normal manner described
previously until it returns to sleep.
Sleeping routers
The Sleeping Router feature of DigiMesh makes it possible for all nodes in the network to synchronize
their sleep and wake times. All synchronized cyclic sleep nodes enter and exit a low power state at the
same time. This forms a cyclic sleeping network.
Devices synchronize by receiving a special RF packet called a sync message sent by a device acting as
a sleep coordinator. A device in the network becomes a sleep coordinator through a process called
nomination. The sleep coordinator sends one sync message at the beginning of each wake period. The
device sends a sync message as a broadcast that is repeated by every device in the network. To
change the sleep and wake times for the entire network, change the settings on an individual node
locally. The network uses the most recently set sleep settings.
For more information, see Become a sleep coordinator.
Sleep coordinator sleep modes in the DigiMesh network
In a synchronized sleeping network, one node acts as the sleep coordinator. During normal
operations, at the beginning of a wake cycle the sleep coordinator sends a sync message as a
broadcast to all nodes in the network. This message contains synchronization information and the
wake and sleep times for the current cycle. All cyclic sleep nodes that receive a sync message remain
awake for the wake time and then sleep for the specified sleep period.
The sleep coordinator sends one sync message at the beginning of each cycle with the current wake
and sleep times. All router nodes that receive this sync message relay the message to the rest of the
network. If the sleep coordinator does not hear a rebroadcast of the sync message by one of its
immediate neighbors, then it re-sends the message one additional time.
If you change the SP or ST parameters, the network does not apply the new settings until the
beginning of the next wake time. For more information, see Change sleep parameters.
A sleeping router network is robust enough that an individual node can go several cycles without
receiving a sync message, due to RF interference, for example. As a node misses sync messages, the
time available for transmitting messages during the wake time reduces to maintain synchronization
accuracy. By default, a device reduces its active sleep time progressively as it misses sync messages.
Synchronization messages
A sleep coordinator regularly sends sync messages to keep the network in sync. Unsynchronized
nodes also send messages requesting sync information.
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