What is the difference between PROFINET RT and IRT?

Both PROFINET Real Time (RT) and PROFINET Isochronous Real Time (IRT) can be used to deliver data within a PROFINET network.

The general difference is that all PROFINET components are equipped with PROFINET RT, fulfilling the majority of the automation timing requirements. PROFINET IRT is al and required only in just high-performance applications.

PROFINET RT handles the time-critical data exchange functioning in the way that when an RT frame arrives in the destination node, the frame is directed from Layer 2, directly to the PROFINET Layer 7, skipping the TCP/IP layers - thus improving the speed and determinism. The end performance overall depends on the network design but cycle times 512 ms down to 250 µs are possible to achieve.

PROFINET IRT goes a step beyond the RT, eliminating the variable data delays (jitter) in high network traffic by enhancing the rules for the Ethernet traffic and creating special rules for PROFINET traffic. Fulfills all synchronization requirements allowing a deterministic communication with 31.25 µs and one µs of jitter.

When it comes to special requirements, there are only a few for IRT, but not for RT. PROFINET RT supports wireless communication via Wi-fI or Bluetooth, but not IRT, because of the variable times it takes to convert wired signals to wireless communication and vice versa.