Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 338)

Section 8. Operation
338
8.5.3.3 Hello-request (one-way broadcast)
All nodes hearing a hello-request broadcast (existing and potential neighbors) will
issue a hello-message to negotiate or re-negotiate a neighbor relationship with the
broadcasting node.
8.5.3.4 Neighbor Lists
PakBus® devices in a network can be configured with a neighbor list. The CR800
sends out a hello-message to each node in the list whose CVI has expired at a
random interval
1 . If a node responds, a hello-message is exchanged and the node
becomes a neighbor.
Neighbor filters dictate which nodes are neighbors and force packets to take
routes specified by the network administrator. LoggerNet, which is a PakBus
®
node, derives its neighbor filter from link information in the LoggerNet Setup
device map.
1
Interval is a random number of seconds between the interval and two times the interval, where the
interval is the CVI (if non-zero) or 300 seconds if the CVI setting is set to zero.
8.5.3.5 Adjusting Links
PakBusGraph, a client of LoggerNet, is particularly useful when testing and
adjusting PakBus
® routes. Paths established by way of beaconing may be
redundant and vary in reliability. Redundant paths can provide backup links in the
event the primary path fails. Redundant and unreliable paths can be eliminated by
activating neighbor-filters in the various nodes and by disabling some beacons.
8.5.3.6 Maintaining Links
Links are maintained by means of the CVI (communications verification interval).
The CVI can be specified in each node with the Verify Interval setting in
DevConfig (ComPorts Settings). The following rules apply:
Note During the hello-message, a CVI must be negotiated between two
neighbors. The negotiated CVI is the lesser of the first node's CVI and 6/5ths of
the neighbor's CVI.
• If Verify Interval = 0, then CVI = 2.5 x Beacon Interval*
• If Verify Interval = 60, then CVI = 60 seconds*
• If Beacon Interval = 0 and Verify Interval = 0, then CVI = 300 seconds*
• If the router or master does not hear from a neighbor for one CVI, it begins
again to send a hello-message to that node at the random interval.
Users should base the Verify Interval setting on the timing of normal
communications such as scheduled LoggerNet-data collections or datalogger- to-
datalogger communications. The idea is to not allow the CVI to expire before
normal communications. If the CVI expires, the devices will initiate hello-
exchanges in an attempt to regain neighbor status, which will increase traffic on
the network.