Campbell Scientific CR1000 Measurement and Control System - Manual (Page 354)

Section 8. Operation
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Discovery occurs when nodes exchange hellos. A hello-exchange occurs during a
hello-message between two nodes.
8.5.3.1 Hello-message (two-way exchange)
A hello-message is an interchange between two nodes that negotiates a neighbor
link. A hello-message is sent out in response to one or both of either a beacon or a
hello-request.
8.5.3.2 Beacon (one-way broadcast)
A beacon is a broadcast sent by a node at a specified interval telling all nodes
within hearing that a hello-message can be sent. If a node wishes to establish itself
as a neighbor to the beaconing node, it will then send a hello-message to the
beaconing node. Nodes already established as neighbors will not respond to a
beacon.
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
CR1000 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.