XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
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cycle the sleep coordinator will send 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
receiving a sync message will remain awake for the wake time and then sleep for the sleep period specified.
The sleep coordinator will send one sync message at the beginning of each cycle with the currently configured
wake and sleep times. All router nodes which receive this sync message will relay the message to the rest of
the network. If the sleep coordinator does not hear a re-broadcast of the sync message by one of its
immediate neighbors then it will re-send the message one additional time. It should be noted that if SP or ST
are changed, the network will not apply the new settings until the beginning of the next wake time. See the
Changing Sleep Parameters section below for more information.
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 in the wake time is reduced to maintain synchronization accuracy. By default, a module
will also reduce its active sleep time progressively as sync messages are missed.
Synchronization Messages
A sleep coordinator will regularly send sync messages to keep the network in sync. Nodes which have not
been synchronized or, in some cases, which have lost sync will also send messages requesting sync
information.
Deployment mode is used by sleep compatible nodes when they are first powered up and the sync message
has not been relayed. A sleep coordinator in deployment mode will rapidly send sync messages until it
receives a relay of one of those messages. This allows a network to be deployed more effectively and allows a
sleep coordinator which is accidentally or intentionally reset to rapidly re-synchronize with the rest of the
network. If a node which has exited deployment mode receives a sync message from a sleep coordinator
which is in deployment mode, the sync will be rejected and a corrective sync will be sent to the sleep
coordinator. Deployment mode can be disabled using the sleep options command (SO).
A sleep coordinator which is not in deployment mode or which has had deployment mode disabled will send a
sync message at the beginning of the wake cycle. The sleep coordinator will then listen for a neighboring node
to relay the sync. If the relay is not heard, the sync coordinator will send the sync one additional time.
A node which is not acting as a sleep coordinator which has never been synchronized will send a message
requesting sync information at the beginning of its wake cycle. Synchronized nodes which receive one of these
messages will respond with a synchronization packet. Nodes which are configured as non-sleep coordinators
(using the SO command) which have gone six or more cycles without hearing a sync will also send a message
requesting sync at the beginning of their wake period.
The following diagram illustrates the synchronization behavior of sleep compatible modules:
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