User's Manual

Street Light Bridge Integrator’s Guide 43
Scenario 1: Loss of SLB A
When SLB A fails (for example, it experiences a power outage), any
communications initiated by the
Segment Controller cannot reach SLB B or the
street light (SL).
At this point, SLB B determines that the RF channel is idle. After the channel
has been idle for 15 minutes, SLB B tunes to another channel from its configured
channel list. If that channel is also idle, SLB B cycles through all of its
configured channels to attempt to reestablish communications. SLB B cycles
through all of its defined channels until SLB A rejoins the network.
When SLB A becomes active, SLB A and SLB B negotiate a new primary channel
for communications. Because the two Street Light Bridge modules are likely not
to be using the same channel at the same time when SLB A rejoins the network,
both cycle through their defined channels until communications are established.
By default, the cycle time is approximately 3 minutes for each channel.
If SLB A had been offline for less than 15 minutes, RF communications would be
reestablished immediately because SLB B would not have switched from the
original channel and SLB A, after it becomes active, would use the same channel.
Scenario 2: Brief Loss of SLB B
If SLB B experiences a brief outage (less than 15 minutes), communications
between the Segment Controller and SLB B or the street light (SL) fail. When
SLB B becomes operational, RF communications are reestablished quickly as the
devices negotiate the use of the channel.
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
(SL) 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.