The question came up at the PROFINET one-day training class in Vancouver: “Is PROFINET routable?” In other words, can PROFINET messages be sent through a router?
First, a little background. In an Ethernet network, several types of device can be used: hubs, switches, and routers. Each works at a different layer of the ISO/OSI reference model. Here is a summary of the ISO/OSI reference model:
(click for larger image)
Hubs work at layer 1 of the ISO/OSI seven layer model. Hubs are not recommended for industrial networks because they send an incoming message on any port out of every other port. This creates too much traffic to maintain deterministic behavior on the network. Switches operate at layer 2. In the Ethernet world this uses the physical address of the device – the MAC address. Layers 3 (IP) and 4 (TCP or UDP) are not involved. Routers use layer 3 and communicate using the IP address. Routers are necessary when communicating from one subnet to another. (For more on subnets, see our archived webinar, “Industrial Ethernet, Advanced Ethernet Architecture.”)
PROFINET communicates in two ways: via TCP/IP and via the PROFINET real-time channel. The PROFINET real-time (RT) channel basically skips the TCP/IP portion of the communications stack. In other words, PROFINET RT uses layers 1, 2, and 7 of the ISO stack just like PROFIBUS and other fieldbuses do. We do this to reduce jitter. But since it does not use IP, it can’t pass through a router. Fortunately, PROFINET CBA (Component Based Automation, our peer-to-peer communications) allows us to use TCP/IP for communications, too… and that is routable. So the short answer after the long background: Yes, PROFINET is routable using PROFINET CBA. (Caveat: using TCP/IP and going through a router will introduce some modest delays compared to PROFINET RT.)
More on the Vancouver class: Most attendees indicated on the course evaluations that the course length was “just right” and several though it “too long.” Perhaps best summarized by someone as “Long, but good.” I agree that it was too long, actually. A couple folks suggested we cut the introduction down. We will have that done before our next class in Boston on July 23.
“Effective use of our time. Webinars are a great feature.”
“Worked well with two instructors (also there was consistency with the webinars).” [You can find those webinars here.]
“Well paced. Well led.”
“Instructors have impressive knowledge of PROFINET.” [They probably meant Hunter, but I’ll bask in his reflected glory.]