Like its predecessor PROFIBUS, PROFINET is a diagnostic-rich protocol allowing your support team to quickly identify the source of device-related problems. This however is of limited use if the underlying performance of your network is poor. PROFINET networks are often seen as the plug and play solution for industrial networks, giving you the impression that successful completion of your application-specific testing is a guarantee that your network is working efficiently and without errors. This is fundamentally wrong and needs to be considered at the design stage as well as the acceptance stage of a project. This presentation will discuss the issues, how to address them and give typical examples of the equipment required.