Unicast / Multicast AB to Adapter

We have a CompactLogix processor (1769-L32E) connected via Ethernet and a switch to one or more 22-COMM-E adapters and then on to Powerflex 4 drives.

We were asked by a potential customer if the communications were 'Unicast'. Assuming that the CPU has its IP address and the adapter has another any communications would be directly between the two (using the standard I/O messaging as well as Explicit Messaging)

But the setup tabs have a checkbox about using Unicast over Ethernet I/P. When would communications NOT be Unicast - even if the checkbox was not checked? I guess I'm showing my ignorance in this matter.

The default mechanism for many years was that I/O modules would Produce their data with Multicast addressing. Produced Tags by a controller also used Multicast addressing.

The idea was that Multicast traffic could be easily consumed by multiple controllers, and that simple IGMP Snooping would constrain that multicast traffic to the nodes of the network that required it.

RA underestimated the appetite of their users for cheap network hardware, and eventually RA made Unicast data production the default mechanism in RSLogix 5000 v18.

There is a detailed summary of unicast vs. multicast traffic, and its implementation history in RSLogix 5000, in the RA Knowledgebase as Article ID # 66324 (Access Level: Everyone).

Thanks, I'll look at the note.