Modern industrial Ethernet/IP networks are robust and capable of communicating with a considerable amount of data. However, all systems have limitations, and often by nearing these limitations, the performance and reliability of the Ethernet/IP network can deteriorate.
There are two primary methods that we can use to resolve or avoid such performance and reliability issues.
Optimise the Tag Sets,
A common issue is that the number of Tag Sets being communicated over the Ethernet/IP network may be nearing the maximum for certain devices. As this limit can change based on the device in question, it is a good idea to optimise Tag Sets such that only one input and/or one output Tag Set is used for each device connection.
Please see the below article for guidance on how to optimise the Tag Sets.
Optimising Ethernet/IP Tag Sets with CX-One's Network Configurator
Scenario When using Ethernet/IP communications between PLCs and other devices,
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Calculate the Bandwidth Usage,
Bandwidth usage is defined in terms of packets per second, or PPS. Each device has a maximum PPS that it can send and receive, with some examples below:
- NX701 CPU Unit: 40 000 PPS
- NX102 CPU Unit: 12 000 PPS
- NX1P2 CPU Unit: 3 000 PPS
- NJ-Series CPU Unit: 3 000 PPS (Except units of version 1.00 to 1.02, which have a PPS of 1 000)
To calculate the bandwidth usage for a device, we need to calculate the PPS of each connection to that device using the RPI, or Request Packet Interval, and the below formula. Note that each connection may have a different RPI.
PPS for a connection = (1000 / RPI (ms)) + (1000/Heartbeat Transmission Period (ms))
Where Heartbeat Transmission period is equal to either the RPI of the connection or 100ms, whichever is greater.
Once the PPS is found for each connection to a device, sum the totals to obtain the total PPS for that device. Compare this value to the maximum PPS for that device.
If the calculated total is near to or exceeds the maximum PPS for the device, increasing the RPI can improve network performance. However, it is important to remember that the RPI specifies the data transmission period, and therefore an overly long RPI may cause lag in communications.