Topology: Chicken feet or palm trees?

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I love some of the terminology that Ian Verhappen uses in “One Network Topology Is Not a Silver Bullet” at ControlDesign.com.  But I have to correct some Industrial Ethernet misconceptions.

Ian is right when he notes that the default Ethernet topology is the star… but that is only right in the office.  For PROFINET any topology is the “default.”  Star, linear, tree, ring, and wireless are all possible with PROFINET.  Ian also talks about ring topologies with slow failover times (Rapid Spanning Tree Protocol – RSTP) and fast failover times for Industrial Ethernet – which he characterizes as proprietary.  That may have been the case once, but that was long ago for PROFINET.  PROFINET offers an open standard for bumpless redundancy.  And it appears that Ethernet/IP now has an open standard for some level of redundancy as well.  For details of PROFINET topology see my blog post: “PROFINET is not a Star.”

That terminology I love in the article: “Many people call a chickenfoot installation a tree; however, the only tree it could represent is a palm tree with all the leaves at the top.”  Of course, here in Scottsdale we have plenty of palm trees, so leaves at the top is easy to visualize.

I have to agree with Ian’s conclusion: “No one network is the right answer in every situation, which means that engineering and thought is required to determine the optimal solution.”  Reminds me of my frequent comment: “There’s no substitute for doing the engineering.”

–Carl Henning

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