© 2014 Digi International Inc. 51
XBee/XBee-PRO
®
DigiMesh 2.4 User Manual
Becoming a Sleep Coordinator
A node can become a sleep coordinator in one of four ways:
Preferred Sleep Coordinator Option
A node can be specified to always act as a sleep coordinator. Do this by setting the preferred
sleep coordinator bit (bit 0) in the sleep operations parameter (SO) to 1. A node with the sleep
coordinator bit set will always send a sync message at the beginning of a wake cycle. For this
reason, it is imperative that no more than one node in the network has this bit set. Although it is
not necessary to specify a preferred sleep coordinator, it is often useful to select a node for this
purpose to improve network performance. A node which is centrally located in the network can
serve as a good sleep coordinator to minimize the number of hops a sync message must take to
get across the network. A sleep support node and/or a node which is mains powered may be a
good candidate.
Use the preferred sleep coordinator bit with caution. The advantages of using the option become
weaknesses when used on a node that is not positioned or configured properly. The preferred
sleep coordinator option can also be used when setting up a network for the first time. When
starting a network, a node can be configured as a sleep coordinator so it will begin sending sleep
messages. After the network is set up, disable the preferred sleep coordinator bit.
Nomination and Election Option
Nomination is an optional process that can occur on a node in the event that contact with the
network sleep coordinator is lost. By default, this behavior is disabled. This behavior can be
enabled with the sleep options command (SO). This process will automatically occur in the event
that contact with the previous sleep coordinator is lost. Any sleep compatible node which has this
behavior enabled is eligible to become the sleep coordinator for the network. If a sleep compati-
ble node has missed three or more sync messages and is not configured as a non-sleep coordi-
nator (presumably because the sleep coordinator has been disabled) it may become a sleep
coordinator. Depending on the platform and other configured options, such a node eventually
nominates itself after a number of cycles without a sync. A nominated node will begin acting as
the new network sleep coordinator. It is possible for multiple nodes to nominate themselves as
the sleep coordinator. If this occurs, an election will take place to establish seniority among the
multiple sleep coordinators. Seniority is determined by four factors (in order of priority):
1 Newer sleep parameters: a node using newer sleep parameters (SP/ST) is considered
senior to a node using older sleep parameters. (See the Changing Sleep Parameters section
below.)
2 Preferred Sleep Coordinator: a node acting as a preferred sleep coordinator is senior to
other nodes.
3 Sleep Support Node: sleep support nodes are senior to cyclic sleep nodes. (This behavior
can be modified using the SO parameter.)
4 Serial number: in the event that the above factors do not resolve seniority, the node with
the higher serial number is considered senior.
Commissioning Button Option
The commissioning button is used to select a module to act as the sleep coordinator. If the com-
missioning button functionality is enabled, a node can be immediately nominated as a sleep
coordinator by pressing the commissioning button twice or by issuing the CB2 command. A node
nominated in this manner is still subject to the election process described above. A node config-
ured as a non-sleep coordinator will ignore commissioning button nomination requests.
To Next Page
Loading...
Need help?
General
