Campbell Scientific CR1000 Measurement and Control System - Manual (Page 355)

Section 8. Operation
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• 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.
8.5.4 PakBus Troubleshooting
Various tools and methods have been developed to assist in troubleshooting
PakBus® networks.
8.5.4.1 Link Integrity
With beaconing or neighbor-filter discovery, links are established and verified
using relatively small data packets (hello-messages). When links are used for
regular telecommunications, however, longer messages are used. Consequently, a
link may be reliable enough for discovery using hello-messages but unreliable
with the longer messages or packets. This condition is most common in radio
networks, particularly when maximum packet size is >200.
PakBus ® communications over marginal links can often be improved by reducing
the size of the PakBus ® packets with the Max Packet Size setting in DevConfig
Advanced tab. Best results are obtained when the maximum packet sizes in both
nodes are reduced.
8.5.4.1.1 Automatic Packet-Size Adjustment
The BMP5 file-receive transaction allows the BMP5 client (LoggerNet) to specify
the size of the next fragment of the file that the CR1000 sends.
Note PakBus ® uses the file-receive transaction to get table definitions from the
datalogger.
Because LoggerNet must specify a size for the next fragment of the file, it uses
whatever size restrictions that apply to the link.
Hence, the size of the responses to the file-receive commands that the CR1000
sends is governed by the Max Packet Size setting for the datalogger as well as
that of any of its parents in the LoggerNet network map. Note that this calculation
also takes into account the error rate for devices in the link.
BMP5 data-collection transaction does not provide any way for the client to
specify a cap on the size of the response message. This is the main reason why the
Max Packet Size setting exists. The CR1000 can look at this setting at the point
where it is forming a response message and cut short the amount of data that it
would normally send if the setting limits the message size.