Thanks for the suggestion.
In our office we have a test setup with Amazon Echo and our engineer wrote a script on AWS. The voice instructions received by Echo is uploaded to the AWS. The script on the AWS transmits a command to a SmartTILE-based PLC (which acts as a TCP-to-RS485 gateway) using the web services command HTTP GET /HOSTLINK/[actual hostlink command].
The gateway is connected to a network of specialty lighting control PLC called ALEC (see
http://ALEC.TRIPLC.COM). These ALEC are connected to the gateway via isolated RS485. The hostlink commands received by the gateway is then dispatched to each individual ALEC.
With this setup we only need to port forward to a single gateway from the public internet. Yet, we now can turn ON/OFF and set the brightness of the lights in any lighting zone using voice command.
Of course if the Google Home can support Modbus/TCP command it would be even more efficient as HTTP protocols involved quite a lot of overhead just to transmit a small amount of data. But it is still possible to achieve the goal using only what our PLCs currently have, and we have demonstrated how it can be done.