Sleep modes
Sleep coordinator sleep modes in the DigiMesh network
XBee 868LP RF Modules User Guide
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If you do not use one of these two methods, you must wait for the network to wake up before adding
the new node.
Place the new node in range of the network with a sleep/wake cycle that is shorter than the wake
period of the network.
The new node periodically sends sync requests until the network wakes up and it receives a sync
message.
Change sleep parameters
To change the sleep and wake cycle of the network, select any sleep coordinator capable node in the
network and change the
SP
and/or
ST
of the node to values different than those the network
currently uses.
n
If you use a preferred sleep coordinator or if you know which node acts as the sleep
coordinator, we suggest that you use this node to make changes to network settings.
n
If you do not know the network sleep coordinator, you can use any node that does not have the
non-sleep coordinator sleep option bit set. For details on the bit, see
When you make changes to a node’s sleep parameters, that node becomes the network’s sleep
coordinator unless it has the non-sleep coordinator option selected. It sends a sync message with the
new sleep settings to the entire network at the beginning of the next wake cycle. The network
immediately begins using the new sleep parameters after it sends this sync.
Changing sleep parameters increases the chances that nodes will lose sync. If a node does not receive
the sync message with the new sleep settings, it continues to operate on its old settings. To minimize
the risk of a node losing sync and to facilitate the re-syncing of a node that does lose sync, take the
following precautions:
1. Whenever possible, avoid changing sleep parameters.
2. Enable the missed sync early wake up sleep option in the
SO
command. This option is enabled
by default. This command tells a node to wake up progressively earlier based on the number of
cycles it goes without receiving a sync. This increases the probability that the un-synced node
will be awake when the network wakes up and sends the sync message.
Note
Using this sleep option increases reliability but may decrease battery life. Nodes using this sleep
option that miss sync messages increase their wake time and decrease their sleep time during cycles
where they miss the sync message. This increases power consumption.
When you are changing between two sets of sleep settings, choose settings so that the wake periods
of the two sleep settings occur at the same time. In other words, try to satisfy the following equation:
(SP
1
+ ST
1
) = N * (SP
2
+ ST
2
)
where SP
1
/ST
1
and SP
2
/ST
2
are the desired sleep settings and N is an integer.
Rejoin nodes that lose sync
DigiMesh networks get their robustness from routing redundancies which may be available. We
recommend architecting the network with redundant mesh nodes to increase robustness.
If a scenario exists where 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 (a
catastrophic failure condition), then multiple subnets may arise 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 devices to fix the problem and prevent it from occurring in the future.
