What are the difference between the net load classes?

What are the difference between the so called net load classes in PROFINET? And when talking about net load classes, how does the "communication quality" connects to the net load class?

Net load classes

PROFINET defines the following net load classes:

• CLASS I: Basic robustness against net load
• CLASS II: Standard robustness against net load
• CLASS III: Advanced robustness against net load

Communication quality / security level 1

The communication quality of a device is tested mandatory for normal operation and faulty communication. The device pass conformance test if both tests are passed. The device is being rated into one of the net load class mentioned above.

Normal Operation

In normal operation the device shall always be fully functional. A previously established PROFINET connection shall not be interrupted and a new connection can be established. The device remains synchronized and can be synchronized. The device is still reachable and can send alarms.

The device may respond to non-real-time services (SNMP, http, RPC, …). However, it is not ensured that the non-real-time communication connection is still in function.

Faulty Communication

For faulty communication the device has to continue to run. The device may go to a "defect" state but is not allowed to reboot nor to restart.

A previously established real time cyclic connection (RT or IRT) is no longer assured. The device may not respond to attempts accessing data records and may not send alarm services. Consequently this may lead to a station loss of this device.

However, the device must not disturb other devices.

The device may respond to non-real-time services (SNMP, http, RPC, …). A new PROFINET communication relationship may not be established.

Net load classes and communication quality

The bandwidth for normal operation depends on protocol network services.