User's Manual

44 Planning for the Street Lighting Solution
Simulating Communications Errors
A Street Light Bridge module autonomously determines which frequency to
monitor, and then continues using this frequency until some failure condition
occurs that makes the frequency unusable. When determining which channel to
use, the Street Light Bridge firmware monitors the channel quality and the
signal quality for the channel, and chooses the best transmit and receive channel.
The firmware considers a receive channel bad if the Street Light Bridge module
receives fewer than five valid LonTalk (ISO/IEC 14908-1) packets in a window of
3600 seconds. Street Light Bridge modules send a heartbeat signal periodically
to ensure that the channel is not idle within this window.
Before deploying a street lighting network, or for a field trial, you can simulate
packet errors for receiving messages, transmitting messages, or both. You can
set the simulation mode individually for both the primary and the alternate PL
path and for each of the 16 RF channels.
To enable the error simulation mode, write a non-zero value to both the
nviErrMode and nviErrRate input network variables. By default, both network
variables have a value of 0 (zero) to disable error simulation. The values of these
network variables persist across device reset and power outage.
Writing a non-zero value to the nviErrMode network variable initiates the error
simulation mode, but only if the corresponding error rate, defined by the
nviErrRate network variable, also has a non-zero value. Thus, you can start and
stop error simulation by writing to the nviErrMode network variable.
In addition, error simulation ends after a time period equal to the value of the
nciErrTimeout configuration network variable (a number of minutes, default of
one day, up to a maximum of three days). This timeout value is updated only
while the Street Light Bridge module is powered on; any time spent powered off
is not included in this timeout value.
Because the Street Light Bridge application writes the remaining error
simulation time to onboard flash memory once every 30 minutes, completion of
error simulation might be delayed by up to 30 minutes if the Street Light Bridge
module is powered off or reset during the simulation.
Updating the nviErrRate network variable has the following effect:
• If error simulation is active, the error simulation expiration timer is
restarted with the current nciErrTimeout value. Note that setting the
nviErrRate network variable to zero still causes the error simulation
expiration timer to restart, even though no errors are simulated.
• If error simulation is not active, the value is stored but has no other
immediate effect.
Updating the nviErrMode network variable has the following effect:
• If error simulation is active, and if nviErrMode is not all zeroes, the error
simulation expiration timer is restarted with the current nciErrTimeout
value.
• Setting nviErrMode to all zeroes ends error simulation mode, regardless
of how much time remains.
Updating the nciErrTimeout configuration network variable has the following
effect: