Denver PROFINET Bandwidth

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Rocky Mountain High… er, highlights, from the PROFINET one-day training class in Denver on September 2:  It seems bandwidth was on the minds of some attendees, especially the few IT folks there.  We are always glad to see IT folks attend, of course – anything we can do to help foster IT’s understanding of automation and vice versa is a good thing.  (Check out our PROFINET and IT white paper.)

We had one question during the class that we only partially answered.  “Can you predict the bandwidth utilization of a PROFINET network before you implement it?”  PROFINET does not use multicasting for IO communications, so traffic is not going to be as heavy as on systems that do.  And it’s easy to determine bandwidth utilization of a running system.  Using SNMP (Simple Network Management Protocol) and an SNMP-OPC server such information can be included in an HMI.  Or, for the IT folks, there are plenty of tools available to pull SNMP data from Ethernet switches.  If traffic is a major concern, perhaps due to sharing the infrastructure with non-PROFINET traffic, PROFINET has the capability to reserve bandwidth using IRT (Isochronous Real Time).  This will require that all the devices support IRT even Ethernet switches, but it ensures that the traffic that has to get through will get through.  So, while we can’t predict bandwidth utilization due to the many variables, including non-PROFINET traffic, we use little of it for IO, can reserve some if needed, and make it easy to check while running.

Another bandwidth question was on the Course Evaluation form: “Does encrypted communication affect PROFINET performance?”  For that let’s revisit the University of Michigan study that was reported in the Industrial Ethernet Book: “Performance metrics for Industrial Ethernet”  The University of Michigan tested data transfer using encrypted VPN compared to UDP and discovered a slight delay in transmission due to the increased overhead.  The overhead is not specified in the article, but appears to be minimal.

Another comment on a Course Evaluation needs a response: “I have an impression that all the advantages can be enjoyed [only] in a Siemens controller.”  PROFINET is a multivendor effort and is supported by a broad selection of device manufacturers.  Features can be realized in controllers from any of the manufacturers.  As we heard at our General Assembly Meeting GE joined the growing ranks of PROFINET controller suppliers.  (See our PROFInews North American Edition newsletter article “A Real Event”.)

Also on the Course Evaluation, I thought this remark was unusual, but also illustrates the attention we pay to detail: “The spiral binding was great – plenty of room for notes.”

More PROFINET one-day training classes are coming, including Montreal tomorrow.  We also still have Dallas and Detroit this year for PROFINET (and Omaha and Baltimore for PROFIBUS).  The full one-day training class schedule is here

And don’t miss our new website: All Things PROFINET!

–Carl Henning

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