ABSTRACT
PROFINET (PROcess FIeld NETwork) is differentiated into different performance classes based on various timing requirements. The classes are: NRT (non-real time), RT (real time), and IRT (isochronous real time).
PROFINET IRT is mostly applied in motion control applications with cycle times below 1 ms. Topologies used are star or line. It employs a dynamic frame packing principle which leads to flexible time cycles. It prevents unauthorized entry of hackers into the system and has a highly reliable diagnostic system.
Working of IRT is based on time slice mechanism. Traffic on the IRT network consists of both IRT and RT. Time allocation for IRT and RT traffic is flexible.
IRT traffic follows stringent time schedules. During this time, any non-IRT traffic would be buffered. Once the IRT traffic is over, the buffered traffic would be allowed to pass with the help of switches and regular Ethernet communication will take place.
A particular cycle in PROFINET IRT begins with synchronization of all the devices in the network. This is done by a highly accurate master clock. IRT data is sent in reserved bandwidth (time slices), followed by RT communication. Diagnostic data are sent in standard communication.
