UM0602
Software equipment of the evaluation kit
Doc ID 15114 Rev 2
11/18
4.3.4
Notes and limitations
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This application defaults to using a fixed set of network parameters, with a default
channel setting of 26.
(Remove the #define USE_HARDCODED_NETWORK_SETTINGS line in the
common.h header file to allow the application to dynamically select its network
parameters.)
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Although the example portrays a single sink node that acts as a ZigBee coordinator, the
application could be easily adapted to allow a variant of the sink node that joins the
network as an ordinary ZigBee router so that multiple sinks can be supported.
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This application uses a “push” style of communication, where the sensor sends reports
to the sink without needing to be asked for this data. This is more efficient than a “pull”
model, where a device only transmits data when asked to do so by another device,
because it cuts the amount of traffic in half, thereby reducing the number of collisions
and routing burden in the network.
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The data reports used in this example are fixed size packets (of a size defined by
SEND_DATA_SIZE). The data contents are simply a 16-bit actual temperature value,
measured at the sensor side.
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The application uses a constant called MISS_PACKET_TOLERANCE as a threshold
for fault tolerance. On the sensor, this controls how many message timeouts can be
permitted between the sensor and sink before the sensor decides to attach itself to
a different sink. For a sink, this controls how many data reports can be missed from
a sensor before the sink “forgets” about the sensor (stops maintaining a record of its
attachment). Although bindings are kept on the sink node to track the attached sensors,
these could easily be made temporary (used only for the SINK_READY message) to
allow the sink application to support more nodes without enlarging the binding table,
assuming that the sink application does not care which sensors and how many sensors
are attached to it.
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The sensor advertisement is a broadcast. The behavior of such a broadcast in the
network depends on the network topology and density. ZigBee limits the number of
broadcasts that can be active in a network to 10 to minimize the network disruption and
loss of bandwidth. As this network increases in size or density, the rate of the sensor
advertisement should be reduced in frequency.
