Ethernet/IP bandwidth and number of nodes

andepand

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Join Date
Jan 2017
Location
Amsterdam
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72
Hello,

A while ago I modernised a magazine gathering / filmwrapping machine. This was a fairly big project for which I used an Omron CJ2M as the main PLC, 10 Wago Ethernet/IP fieldbus couplers, a Keyence CV-X420 vision camera and an Omron NS12 HMI.

All of these components run on the same network which contains an unmanaged switch where the HMI, PLC and the first Wago are connected. The Wago’s act as a two port switch since they are all daisy chained. At the end of the Wago chain there is also the vision cam which is connected at the last Wago coupler.

At the time I was advised against using Broadcasting instead of Multicasting with a managed switch, but I tried anyway since my networking knowlege is lacking.

Also, the only ‘bandwidth demanding data’ comes from the vision system. The Wago couplers contain only digital I/O and high speed encoder inputs run directly to the CJ2M.

I haven’t run into any trouble so far and the machine is already producing for over a year.

Now , a new project is on the way and it will need even more Ethernet couplers, 15 to be precise.

This brings me to my question; is there a limit to the number of nodes in an Ethernet/IP network and will I possibly run in to bandwidth problems by adding more remote I/O and not using a mannaged switch? Also, I would like to get high speed input out of one of the Wago couplers.

Thanks in advance for any feedback!

Greetings from Holland

Andy
 
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I'm not aware of any connection limit based on your network, it all depends on the traffic.

But to your comment about managed switches, my understanding is that just about any decent industrial unmanaged switch supports multicast (and maybe unicast?) these days, so you don't have to worry about spamming broadcasts from every device.

The advantage of a managed switch would be the additional features (VLANs, troubleshooting, etc) but not necessarilly increased performance. I have pretty decent size control systems running nothing but unmanaged switches and don't have any issues with performance.
 
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Unless you are using multiple consumers for data you are always better off using unicast. An unmanaged switch will be sending the multcast traffic to every port. Switches these days have pretty massive bandwidth so that is probably not a problem. Make sure the devices all support full duplex or you increase the chances of collisions between the switch and devices.
 
I understand the use of VLAN and the ability to troubleshoot a network using a managed switch, but I’m having a hard time understanding how multicast and unicast are being handeled by different sorts of switches.
And also if the CJ2M network should be configured differently.

Looking at both your replies I reckon my current way of setting up things should be fine, but I’m eager to learn more about it.
 
While you don't see it on the IO, there is a third port that is dedicated to the module itself. By using broadcast, you're forcing whatever little processing power the IO has to receive each packet from the vision system, inspect it, determine it has no use for it, and then finally discard it. Not a great deal of work, but unnecessary work for the IO to be doing. Using unicast will pass those vision system packets directly to whichever device needs them and bypass all other hosts.
 
Clear info. Buying an intelligent switch is no problem but I can’t inmagine it’ll just know what to do out of the box.

Offcourse I will check out available documentation I can find but maybe someone can explain me some basics. For example, is it just a matter of forwarding ports or IP adresses in the switch configuration or should I configure the network in a special way in CX programmer?

Omron doesn’t seem to have much support on this matter.
 
You likely don't need a new switch for this expansion. If this were mine, I'd keep all the IO together as one physical network segment that plugs into one port on the switch. I'd homerun the camera to its own port on the switch. The PLC and the HMI would also have their own ports on the switch. Set that camera to unicast or at least multicast, just not broadcast. Quite frankly, I'm surprised that broadcast is an option in that device. If the wiring isn't an issue that's difficult too do, I'd break those IO up into maybe 4 physical segments (chains) and have them occupy 4 ports on your switch. This will reduce latency. If they're all in one chain, that last IO's data will have to be switched about 16 times before it gets to the PLC. Not a huge impact, but your high speed data may suffer a bit. Consider giving each high speed input its own homerun ethernet cable directly to the switch if you see latency problems.

Adding a managed switch adds the ability to see port counters, error logs, and VLANs in some cases. This is stuff you probably don't need.
 
I was indeed planning on giving the vision system it’s own line to the switch.
Probably I explained it wrong, the camera actually has no settings for broadcast, unicast or multicast. Just a target IP adress, node number and some additional port settings etc.
So no idea how it handles things, I suppose that’s depending on the PLC’s configuration?

Breaking the remote I/O up in segments is also something to consider, didn’t think of that.

Big thanks to all of you for your time and knowlege.

Greetings,

Andy
 

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