Profinet (usually styled as PROFINET, as a portmanteau for Process Field Net) is an industry technical standard for data communication over Industrial Ethernet, designed for collecting data from, and controlling equipment in industrial systems, with a particular strength in delivering data under tight time constraints (on the order of 1ms or less).

There is 2 versions of Profinet with many protocol inside, and more all the time.

Profinet RT: This process data and alarms are always transmitted in real time (RT). Real time in PROFINET is based on the definitions of IEEE and IEC, which allow for only a limited time for execution of real-time services within a bus cycle. RT communication represents the basis for the data exchange in a PROFINET system. Real-time data are treated with a higher priority than TCP(UDP)/IP data. This type of data exchange allows bus cycle times in the range of 10 ms. Some people will try for faster then 10ms but that only works if they are not pulling a lot of data out of a device. This data is not synchronized but very good for most all application.

Profinet IRT: This process data uses the transparent clock mechanism to synchronize PROFINET IRT devices. The transparent clock mechanism is specified in IEEE 1588-2008 (1588 V2). This creates one control loop between the master clock and slave clocks. This data is synchronized unlike Profinet RT. That said it is not needed for most systems unless the PLC is producing the full profile and the drive or motion device is just following count / count. if you want to use 1588V2 you have to have special network switches that support PTP (1588v2). This will make things cost more if the network is in a star configuration.