# Rockwell PLC Comms Overhead

**URL:** <https://forum.inductiveautomation.com/t/rockwell-plc-comms-overhead/76164>\
**Category:** Ignition\
**Created:** [July 10, 2023, 9:51pm UTC](https://forum.inductiveautomation.com/t/rockwell-plc-comms-overhead/76164 "2023-07-10T21:51:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![cvanremoortel](https://avatars.discourse-cdn.com/v4/letter/c/ba8739/32.png) [@cvanremoortel](https://forum.inductiveautomation.com/u/cvanremoortel)\
**Post date:** [July 10, 2023, 9:51pm UTC](https://forum.inductiveautomation.com/t/rockwell-plc-comms-overhead/76164/1 "2023-07-10T21:51:27Z")

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A customer has a number of PLCs both they and I need to subscribe to. The tags I subscribe do not overlap the tags they subscribe to. Is there any advantage to having one tag gateways subscribe to all the tags and then use a gateway network to distribute as needed vs. having two tag gateways connect to a PLC?

Thanks,

Chris

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [July 10, 2023, 10:13pm UTC](https://forum.inductiveautomation.com/t/rockwell-plc-comms-overhead/76164/2 "2023-07-10T22:13:41Z")

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If you mean they subscription lists don't overlap at all, that is, the first symbol in a controller tag item path, or the first symbol after the program folder, then no, no advantage either way.

But keep in mind that the top level tag is the core unit of optimization, so elements of arrays or UDTs underneath a top level tag can be read together at high efficiency by single polling server. Even if you aren't overlapping at the leaf items, if you are overlapping at top level tags, you should consider using a single polling server.

But do also note this topic:

> [@Cannot read some tags inside Rockwell AOI](https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393/3):
>
> What Mike said, but also: Don’t. All AOI’s have EnableIn and EnableOut booleans that are locked to “Hidden” and therefore prevent most optimization of the data traffic to read instances of these data types. Ignition’s Logix driver cannot do bulk reads on AOIs. Do very much of this and your Logix driver will choke. I strongly recommend that any AOI you design yourself use one or more InOut parameters of another data type, with instances of those datatypes elsewhere. Place all of your extern…

(Many links to follow from that, too.)