Maximum network bandwidth equals your network speed, for example 100 Mbps. When designing your control network, allocate network bandwidth among the control application messages required by your application.
NOTE: Schneider Electric recommends you reserve at least the following amounts for processing explicit messaging:
Message Load and Message Bandwidth
Message Load—in packets per second (PPS)—represents the number of packets in a single message that are received and sent within one second.
Message Load can be estimated as follows:
Message Load =
(number of packets per connection) x (number of connections) / RPI
The number of packets per connection value depends on the capacity of the device, and can be either:
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1: for connections that support uni-directional communication
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2: for connections that support input and output (for producer/consumer mode) or request and response (for client/server mode) per one time bi-directional exchange, or
The connection can be used for either explicit or implicit messaging. For UDP-based explicit messaging, assume that each client represents one connection, and that messages are transmitted cyclically.
Message Bandwidth (in bits) can be calculated as follows:
Message Bandwidth = message packet size (bits) x Message Load
Based on the portion of network bandwidth you want to allocate to a particular message, you can use the Message Load and Message Bandwidth formulae to calculate the fastest RPI for the message.
Device Load and Device Bandwidth
Device Load—measured in number of packets—represents the load contributed by messages received and sent by a device within one second.
Device Load is the sum of the
Message Load values for every message 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 messages handled by the device
In your control application design, 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 every remote device.
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:
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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.
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Increase the RPI setting for a device where possible.
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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 the adapter devices, or of the scanner devices.
Network Bandwidth—measured in bits—can be estimated as the sum of the
Device Bandwidth of the adapter devices, or 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:
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adjusting device RPI settings
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changing connection types (e.g., from direct to rack optimized)
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modify the configuration
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change the network topology
