Imagine that you wanted to allocate 25% of a network’s bandwidth to IRT traffic. A possibility to lock the network data exchange to the real-world I/O data process, eliminating aliasing or other sampling artifacts.With some of the PROFINET V2.3 extensions, IRT networks can operate with cycle times as low as 31.25μs (32,000 samples per second). Fast cycle times: IRT can easily provide cycle times down to 250μs (4,000 samples per second).Deterministic network behavior: frames are transmitted and received on a schedule and in order.Benefits of IRTīy synchronizing the network, IRT provides some benefits over the standard RT communications channel: To meet these requirements, PROFINET designed a MAC-layer extension to Ethernet that allows each switch on an IRT network to provide time slices that turn it in to a TDMA (Time Division Multiple Access) medium part of the time and a regular CSMA-CD medium the rest of the time. Some applications, like closed-loop motion control, require not just low cycle times, they also require deterministic behavior from their network – data should be strictly sequenced and should never be vulnerable to collisions or jitter. When Real-Time Isn’tīut sometimes “Real-Time” isn’t “hard” real time. This is the standard “Real-Time” (RT) PROFINET communications channel.

Using switches, PROFINET Conformance Class A and B devices leverage standard Ethernet infrastructure to achieve cycle times as short as 1 millisecond and jitter of about 10-100μs. Modern Ethernet networks use network switches instead of hubs, which eliminates the possibility of those collisions. This sounds like a terrible basis for a real-time network, but it’s really not that bad. Ethernet calls this concept “CSMA-CD” (Carrier Sense Multiple Access – Collision Detect), and it means that on a common carrier, multiple nodes can access the medium and transmit when they like, and that they are responsible for detecting a collision and retransmitting their data if one occurs. Unless there’s abnormally high bandwidth utilization, Ethernet is built on the assumption that nodes will probably not transmit at the same time.

Ethernet, by definition, is an open network that allows anyone to transmit at any time – making it a probabilistic transmission medium. When you mention the words “real-time” and “Ethernet” in the same sentence, let alone next to each other, you get some incredulous looks.

Profinet communication between plc