Campbell Scientific CR200/CR200X-series Dataloggers - Manual (Page 147)

Section 14. PakBus Overview
14.4.1 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.
14.4.2 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.
14.4.3 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.
14.4.4 Neighbor Lists
PakBus® devices in a network can be configured with a neighbor list. The
router or master sends out a hello-message to each node in the list whose verify
interval has expired at a random interval*. If a node responds, a hello-message
is exchanged and the node becomes a neighbor.
*A random number of seconds between INTERVAL and (2 * INTERVAL),
where INTERVAL is the Verify Interval setting if non-zero, or 30 seconds if the
Verify Interval setting is zero.
Neighbor filters dictate which nodes are neighbors and force packets to take
routes specified by the network administrator. LoggerNet (a PakBus® node)
derives its neighbor filter from link information in the Setup device map.
14.4.5 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.
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