Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 339)

Section 8. Operation
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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 CR800 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 CR800
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 CR800 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.
8.5.4.2 Ping
Link integrity can be verified with the following procedure by using
PakBusGraph Ping Node. Nodes can be pinged with packets of 50, 100, 200, or
500 bytes.
Note Do not use packet sizes greater than 90 when pinging with 100 mW radio
modems and radio enabled dataloggers (see the appendix Telecommunications
Hardware
).
Pinging with ten repetitions of each packet size will characterize the link. Before
pinging, all other network traffic (scheduled data collections, clock checks, etc.)
should be temporarily disabled. Begin by pinging the first layer of links
(neighbors) from the PC / LoggerNet router, then proceed to nodes that are more