Section 8. Operation
8.9.2 Conserving Bandwidth
Some comms services, such as satellite networks, can be expensive to send and
receive information. Best practices for reducing expense include:
• Declare Public only those variables that need to be public.
• Be conservative with use of string variables and string variable sizes.
Make string variables as big as they need to be and no more; remember
the minimum is actually 24 bytes. Declare string variables Public and
sample string variables into data tables only as needed.
• When using GetVariables() / SendVariables() to send values between
dataloggers, put the data in an array and use one command to get the
multiple values. Using one command to get 10 values from an array and
swath of 10 is much more efficient (requires only 1 transaction) than
using 10 commands to get 10 single values (requires 10 transactions).
• Set the CR800 to be a PakBus router only as needed. When the CR800
is a router, and it connects to another router like LoggerNet, it exchanges
routing information with that router and, possibly (depending on your
settings), with other routers in the network.
• Set PakBus beacons and verify intervals properly. For example, there is
no need to verify routes every five minutes if communications are
expected only every 6 hours.
8.9.3 Initiating Comms (Callback)
Comms sessions are usually initiated by a PC. Once comms are established, the
PC issues commands to send programs, set clocks, collect data, etc. Because data
retrieval is managed by the PC, several PCs can have access to a CR800 without
disrupting the continuity of data. PakBus® allows multiple PCs to communicate
with the CR800 simultaneously when proper comms networks are installed.
Typically, the PC initiates comms with the CR800 with datalogger support
software
(p. 572). However, some applications require the CR800 to call back the
PC (initiate comms). This feature is called 'Callback'. Special LoggerNet
(p. 572)
features enable the PC to receive calls from the CR800.
For example, if a fruit grower wants a frost alarm, the CR800 can contact him by
calling a PC, sending an email, text message, or page, or calling him with
synthesized-voice over telephone. Callback has been used in applications
including Ethernet, land-line telephone, digital cellular, and direct connection.
Callback with telephone is well documented in CRBasic Editor Help (search term
"callback"). For more information on other available Callback features, manuals
for various comms hardware may discuss Callback options.
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