AlfredoQuintero said:
Hello Geospark:
I believe the advise of our colleagues is based not on Ethernet communication considerations, but from the point of view of system documentation, maintenance, cabling labeling considerations. Imagine there is a problem on New Years Eve and there is no sober IT guy around. Having a system properly documented, cables properly labeled, etc., can be crucial in diagnosing and fixing certain issues, without IT specialist or PLC developer.
Hi,
Yes, I do/did consider this. I did mention how I can be O.C.D. with the order of things, in any design. But "this" should not matter, if done properly. If you drop a new 192.168.1.100 node into an existing ring topology, where the highest previous node is 192.168.1.10, and label it as such, then the next person to deal with this system should be relying on those very document updates you speak of, which should now include this new node number, which has its new and correct labelling. You should not need (or want?) to start shifting existing nodes, cabling, labelling, configurations and schematics around.
If someone is viewing Industrial Ethernet layout schematics, and expecting everything to be perfectly sequential, or else their head might explode (exaggeration, of course), then really they should not be viewing them in the first place. 10 loops to 100 and then on to 20. It looks strange, perhaps, and one might wonder why it was done that way, buy if the schematics match the installation, all should be well.
I'm using a distant node number (100) just as an example of how little it should matter. Of course, just because we are dealing with an Ethernet ring topology does not mean we have a closed loop with respect to available node numbers. A ring topology, like any other topology, will have a lowest to highest node numbering schema. So realistically speaking, there should always be a next highest node number available (11 after 10) or a next node number within each decade of nodes, depending on the schema (11 after 10 or 21 after 20, etc.). Leaving spare node numbers in between existing nodes is often done for this reason. Node 1 is 10, 2 is 20, etc. This way if you add a node physically, or otherwise, after 10, it can be 11, with still further spares up to 19. Also, as a ring topology can be physically spread out between different areas, say on a production line, or different steps in a process, we would/should use a segregated schema. Either under the same Subnet with grouping, as I've outlined just now (nodes 10+ for area 1, nodes 20+ for area 2, nodes 30+ for area 3, etc.), or using segregation by VLANs where each designated area in an installation is given its own "Subnet", if you will. With VLANs, two separate areas or machines could even be using identical IP node addressing, but the VLAN number for each area will be the unique identifier.
You should just install the device where it is physically intended to go and cable to it in the best or simplest manner you see fit. The addressing applied should not need to be specific in accordance with its position on the ring, but should be in keeping with the IP addressing schema for the system.
Even for a new installation this should apply. If I have a DLR controller in a right side cubicle with a DLR HMI on the door. Also 10 DLR drives in a left side cubicle, in two rows of 5, one above the other. I then have a passthrough hole in the centre. The first loop from the controller could physically go to drive 5, then looping back left through to drive 1, then looping down to drive 6, and right through to drive 10. The last loop could go back through and up to the HMI, and then back to the controller. Physically, this may have been the best way to root the ring cabling. The controller is node 1, HMI is 2, and the drives are nodes 3 through 12. If you say you'd prefer to go from the controller(1) to the HMI(2), then to drive(3), and so on, with the cabling, then that is fine, and your prerogative. But all I am saying is that it is not necessary for any practical reason. If you document it as it is cabled and labelled, then that should be enough for future souls.
Regards,
George