Specifications

Optimizing Performance
102
EIO0000000051 6/2010
Device Load and Device Bandwidth
Device Load—measured in number of packets—represents the load contributed by
all messages received and sent by a device within one second. Device Load is the
sum of the Message Load values for all messages handled by the device.
If the Device Load exceeds the device’s processing capability, performance of both
the device and the network is degraded.
NOTE: Schneider Electric recommends that Device Load not exceed 90% of CPU
processing capacity of each device.
Device Bandwidth—measured in bits—is the sum of the Message Bandwidth values
for all messages handled by the device
In your control application design, you must determine whether the I/O scanner
device can handle the load contributed by every I/O adapter device. To do this,
perform the following steps:
1 Calculate the implicit messaging load and bandwidth for each remote device.
2 Sum the load and bandwidth estimates for all remote devices.
3 Compare the total implicit messaging load and bandwidth against the maximum
implicit messaging capacity of the device acting as I/O scanner.
If the projected total load or bandwidth for a communication module acting as an I/O
scanner exceeds its implicit messaging load or bandwidth limits, consider one or
more of the following corrective actions:
z If the I/O adapter supports rack optimized connections, and if a single rack of
digital I/O uses multiple direct connections, replace the direct connections with a
single rack optimized connection, if possible.
z Increase the RPI setting for a device where possible.
z Add another communication module to act as an I/O scanner, and re-design the
network in order to share the load.
Network Load and Network Bandwidth
Network Load—measured in number of packets—can be estimated as the sum of
the Device Load of all the adapter devices, or all of the scanner devices.
Network Bandwidth—measured in bits—can be estimated as the sum of the Device
Bandwidth of all the adapter devices, or all of the scanner devices.
NOTE: Schneider Electric recommends that Network Load not exceed 90% of
maximum network bandwidth.
If necessary, you may need to optimize your control application design by:
z adjusting device RPI settings
z changing connection types (e.g., from direct to rack optimized)
z modify the configuration
z change the network topology