© 2014 Digi International Inc. 55
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DigiMesh 2.4 User Manual
3 When changing between two sets of sleep settings, choose settings so that the wake periods
of the two sleep settings will happen at the same time. In other words, try to satisfy the
following equation: (SP1 + ST1) = N * (SP2 + ST2), where SP1/ST1 and SP2/ST2 are the
desired sleep settings and N is an integer.
Rejoining Nodes Which Have Lost Sync
Mesh networks get their robustness from taking advantage of routing redundancies which may
be available in a network. It is recommended to architect the network with redundant mesh
nodes to increase robustness. If a scenario exists such that the only route connecting a subnet to
the rest of the network depends on a single node, and that node fails -- or the wireless link fails
due to changing environmental conditions (catastrophic failure condition), then multiple subnets
may arise while using the same wake and sleep intervals. When this occurs the first task is to
repair, replace, and strengthen the weak link with new and/or redundant modules to fix the
problem and prevent it from occurring in the future.
When the default DigiMesh sleep parameters are used, separated subnets will not drift out of
phase with each other. Subnets can drift out of phase with each other if the network is config-
ured in one of the following ways:
• If multiple modules in the network have had the non-sleep coordinator sleep option bit
disabled and are thus eligible to be nominated as a sleep coordinator.
• If the modules in the network are not using the auto early wake-up sleep option.
If a network has multiple subnets that have drifted out of phase with each other, get the subnets
back in phase with the following steps:
1 Place a sleep support node in range of both subnets.
2 Select a node in the subnet that you want the other subnet to sync up with. Use this node to
slightly change the sleep cycle settings of the network (increment ST, for example).
3 Wait for the subnet’s next wake cycle. During this cycle, the node selected to change the
sleep cycle parameters will send the new settings to the entire subnet it is in range of,
including the sleep support node which is in range of the other subnet.
4 Wait for the out of sync subnet to wake up and send a sync. When the sleep support node
receives this sync, it will reject it and send a sync to the subnet with the new sleep settings.
5 The subnets will now be in sync. The sleep support node can be removed. If desired, the
sleep cycle settings can be changed back to what they were.
In the case that only a few nodes need to be replaced, this method can also be used:
1 Reset the out of sync node and set its sleep mode to cyclic sleep (SM = 8). Set it up to have
a short sleep cycle.
2 Place the node in range of a sleep support node or wake a sleeping node with the
commissioning button.
3 The out of sync node will receive a sync from the node which is synchronized to the network
and sync to the network sleep settings.
XBee DigiMesh Diagnostics
The following are useful in some applications when managing a sleeping router network:
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