1. The article is intended to provide instructions of using MQTT between RUT and a Linux PC. No need to install anything else on the router, the commands are meant to be used on the PC side. From the article:
"Once the Broker is up, you'll need install Mosquitto and Mosquitto Clients. To do so, open the Linux Terminal app and enter this command:
$ sudo apt-get install mosquitto mosquitto-clients
"
So the program is meant to act as the MQTT publisher on the PC. This is an example for testing and to understand the capabilities of MQTT on RUTs. I imagine that in reality everyone would use their own MQTT software, so the PC related steps aren't even mandatory.
But I see your point. I'll see what can done to make the guide more intuitive and understandable.
2. I tested remote Modbus TCP access on port 502 with RUT9XX_R_00.06.2 FW and it works as expected. It should be noted that usually a SIM card with a public IP address is required for such remote actions. But not always. For example, if you use an Ethernet (wired) connection as your WAN, you can still test remote access from the same wired network even with a private IP, since the router considers everything coming from a WAN interface as a remote connection.
My test was pretty simple, tell me if I missed something:
3. Would have to do extensive testing on the performance of JSON-RPC to provide any meaningful comment. I have, however, heard of a very similar case where Teltonika's testing department were not able to reproduce the issue. Perhaps some information is missing? Can you describe your testing method in detail so that I can try it myself of give it to Teltonika's testers for thorough analysis?
Yes, most configuration example articles are pretty basic and intended for simple solutions or to be used as overviews of certain functions and their capabilities. In reality, pretty much every solution is different depending on the user, their equipment and other circumstances, so it is near impossible to encompass every possible situation within the documentation. If you have a suggestion for a solution that you would like to see on the Wiki, you can send the information and I'll see what I can do to make it happen.
I'm sorry your experience has been negative thus far. Have you gotten direct support from Teltonika? Where did you purchase the device? You may want to contact your vendor to see if they get direct support from Teltonika. If you have observations like this or encounter bugs, usually the fastest, most effective may to deal with this is contacting the support team (via your vendor; if they provide such a service).