Installation guide

78 Estimating Network Performance
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3.10 Loading Effects in Your Application
During the application, each node on the network can have a different
number of paths constantly being opened, held active, and closing.
This is a dynamic process that is affected by the count of nodes and the
amount of message traffic between them.
If some nodes have most of their paths active at any given moment, and
others do not, the nodes with the heavy path loading will hold the token
longer as they process data. The token will move more slowly through
heavily loaded nodes, and more quickly through those that are lightly
loaded.
The effect on an individual MSTR function in your application will be
quicker completion during light network loading, and slower
completion under heavy loads. Even though the origination and
destination nodes in the MSTR operation may have light path loading,
the network token must still pass through the other nodes. If their
loading is heavy, the net effect will be a slower token rotation time,
affecting both the sending and response of a data request.
Appendix A provides further details about the token holding times in
nodes that are fully loaded with active transactions and queueing.
3.10.1 MSTR Data Path Handling Under Loading
When you program multiple MSTR functions in a controller’s ladder
logic, they will be handled according to loading conditions as follows:
V At the source . If more than four MSTR functions are enabled at
any time (through their ENABLE inputs), the first four scanned
will go active using the MSTR Data Master paths available in the
controller. The other MSTR functions will not be serviced, but will
wait for free paths. Your design of the ladder logic program
controls the sequencing of the MSTR functions.
V At the destination. If the destination controller has all of its Data
Slave paths currently active, the next data transactions will be
queued until paths are available. This queue will be processed at
the approximate rate of four transactions per scan of the controller.
MSTR functions in originating controllers will wait, with their
paths held open, until a final data response is returned from the
destination.