Re: DLR Device Level Ring

  • This topic has 4 replies, 4 voices, and was last updated 2 years ago by PLCGuruPLCGuru.
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    SureshotDavid Garcia
      Karma: 49
      Rank: Padawan

      Hello Everyone,

      What are the Pros and Cons of DLR, and what are some good alternatives for Redundancy at the Device Level.



        Hi David, it’s been a while.

        Well I’m sure you have the basic understanding of what Device Level Ring (DLR) is. It’s basically a way to add single fault tolerance to your automation network so that in the event you lose a communication path the acting “ring supervisor” can recover your network.

        Some of the benefits a DLR and ring supervisor will provide:

        • Helps prevent and manages network loops
        • Determines active or backup status
        • Verifies ring integrity
        • Reconfigures the ring to recover from a network fault
        • Performs ring diagnostics

        To name a few. This is very similar in architecture to a traditional spanning tree protocol (STP). Some of the drawbacks I would say are the following:

        • Added cost due to your distributed I/O adapters requiring two Ethernet ports vs one (however it reduces the main switch size as fewer ports are needed here if at all).
        • You now have to route conduit/cabling from device to device which can be difficult in large distributed systems vs bringing everything back to your main control panel/switch.
        • Adds complexity to the network.

        I’m sure there’s more that can be said, but thought I’d chime in for you here anyway.



        Caioricardo robaudo
          Karma: 28
          Rank: Padawan


          Other drawback  could be that in case of  two interruptions in the ring, (because of maintenance or faults) will leave devices in between uncommunicated.


          SimJeffJeff Simmons
            Karma: 13
            Rank: Padawan

            As with many network methods, it depends.

            When it first was getting popular customers would demand to use it as they thought it gave them redundancy.      But then these would be the same customers that would have a fault happen on Tuesday, claim they will fix it on the weekend, then never fix it until they have a second fault and need to learn the routing of the network to find 2 problems.    When used appropriately, and in the right types of equipment – it can be very handy.       I prefer it in more localized usage – and not for the trunk line of a large system.



            SureshotDavid Garcia
              Karma: 49
              Rank: Padawan

              I figured because of the amount of nodes, that it would be more of a Localized Segment type of solution.
              What alternatives are out there that would be more idea, and is there any limitations as far as integration into larger network?
              By the way… Thank you to everyone on here for being such a great resource for Noobs to this technology. l am really trying to learn more about the different redundant technologies at the device level.
              To help my customers, and give them insights into options for them to get what they need the job done.

              @Simmons, @Ricardo Robaudo , @Graham thank you.



                Agree with Jeff on this one (as I chuckle to myself hearing the underlying synacism – when you’ve been around the block and seen the way things go it’s hard not to be sometimes :).

                But yes, a DLR by definition, is a “Device” Level Ring so it is most practically implemented at the work cell level to provide a level of redundancy in your automation cell.

                For your backbone switches this will typically be handled by “true” layer 3 switches handling your trunk lines and inter-vlan routing. This is the IT to OT bridge if you will connecting your factory floor to your business intelligence systems.

                Enjoy your weekend boys!

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