Campbell Scientific PakBus Networking Guide - Manual (Page 11)

PakBus Networking Guide
paths and possibly using marginal routes of communication. The PakBus
address and the communication interface of the neighbor device in the allowed
neighbor list must be entered correctly for discovery to work.
If communication fails to a node declared in an allowed neighbor list, the
datalogger will continually attempt communication to that node until it is
discovered with a successful hello exchange. The discovery attempt for
devices in the allowed neighbor list is done with a directed hello command that
occurs at two times the verify interval. If the verify interval is zero, the interval
used to verify communication with devices in the allowed neighbor list will be
30 seconds by default. If the beacon interval is non-zero, discovery attempts
for devices in the allowed neighbor list use the standard beacon interval and
message rather than a directed hello message.
These specific intervals and procedures only apply to discovery of devices in
the allowed neighbor list. Please do not confuse the discovery intervals and
procedures for nodes entered in the allowed neighbor list with standard
discovery intervals and procedures used when creating the list of known routes
to PakBus neighbors, which will be discussed later in this document.
If routers on the network are using allowed neighbor lists to filter
communication, they must list each other as potential neighbors in their
respective lists or they will not be able to communicate with each other. Do
not include the datalogger’s own address in the allowed neighbor list.
3.4.3 Program Instructions
A PakBus datalogger can be programmed with instructions that send packets to
other PakBus devices on the network. When a program sends a packet to a
specific PakBus device, the devices discover each other and become neighbors.
Although datalogger program instructions are a direct way to discover
neighbors, they are not very dynamic. The program must be changed and sent
to the datalogger before a new neighbor or communication route can be
discovered.
3.5 Datalogger to Datalogger Communication
One distinct advantage of using PakBus devices is their ability to easily
communicate directly with each other. A datalogger program can contain an
instruction that will send information to a specific PakBus address on the
network. The data packet will be routed through the network to the device
with the address specified in the datalogger program instruction.
Communication and information exchange between PakBus devices using
these program instructions can happen quickly and unattended.
Some of the instructions used to transfer information between devices include
GetVariables, SendGetVariables, and SendVariables. An example of
datalogger to datalogger communication is a datalogger in a remote location
monitoring water levels that is programmed to send a variable to a second
datalogger that controls a gate or pump. Another example is a central
datalogger that collects data from many remote devices and stores that data for
easy retrieval by a computer from a single datalogger.
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