Echelon Lumewave CRD 3000 Street Light Bridge - Manual (Page 54)

44 Planning for the Street Lighting Solution
Scenario 3: Prolonged Loss of SLB B
If SLB B experiences an extended outage (longer than 15 minutes),
communications between the Segment Controller and SLB B or the street light
fail. SLB A detects an idle channel, and begins cycling through the channel list.
If the Segment Controller continues to attempt to communicate with SLB B, SLB
A delays cycling through the channels until the number of failed messages equals
the retry count.
When SLB B becomes operational, it uses its last-known-good channel. If the
Segment Controller has not switched the path (for example, from normal to
alternate), one of the message retries should succeed as SLB A cycles through the
configured channel list. Otherwise, SLB A and SLB B negotiate a new primary
channel for communications. The channel negotiation for downstream
communications (from the Segment Controller) is fairly quick because it
alternates between the primary and the alternate path. For upstream
communications (to the Segment Controller), message retries guarantee that
communications are reestablished.
If the Segment Controller has marked SLB B as “Confirmed Down” (see
Analyzing a Power Line Repeating Network on page 54), reestablishment of
communications could take additional time, depending on the retry timer for
Confirmed Down devices.
Simulating Communications Errors
A CRD 3000 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 CRD 3000 Street
Light Bridge module receives fewer than five valid LonTalk (ISO/IEC 14908-3)
packets in a window of 3600 seconds. CRD 3000 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, for transmitting messages, or for 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 data points. By default, both data points
have a value of 0 (zero) to disable error simulation. The values of these data
points persist across device reset and power outage.
Writing a non-zero value to the nviErrMode data point initiates the error
simulation mode, but only if the corresponding error rate, defined by the
nviErrRate data point, also has a non-zero value. Thus, you can start and stop
error simulation by writing to the nviErrMode data point.
In addition, error simulation ends after a time period equal to the value of the
nciErrTimeout data point (a number of minutes, default of one day, up to a
maximum of three days). This timeout value is updated only while the CRD 3000