Ok. That makes more sense. In that case, no form (or Javascript or Ajax) is necessary.
Obviously, if the BS can't contact the server outside your network (192.) then the outside server is not going to be able to communicate directly to the BS with or without a form.
And, in fact, there is no "client side" where a form would exist.
So you really have three entities: The BS, the computer on your network (you called it the "go between" which it is), and the remote server with the MySQL database. You have two options, both will work very well:
The BS sends a request to the go between computer by requesting a PHP page. Either (A) that PHP page opens a MySQL connection to the remote computer with MySQL and performs a query for the data you want and PRINTS it out (no form), or (😎 that PHP page on the go between performs a second http request to a PHP page on the remote computer that performs the MySQL query locally, PRINTS the result, and the PHP script on the go between relays that information to the BS by, again, simply PRINTING the result.
Forms are for web browsers like Internet Explorer, Firefox, or Safari. You don't need to complicate this with any client side web browsers.
So, for clarity, here are your two options:
- BS -> PHP on go between -> MySQL on remote machine
followed by PHP on go between -> BS
or
- BS -> PHP on go between -> PHP on remote machine -> MySQL
followed by PHP on remote -> PHP on go between -> BS
All server side, no forms.
I'm curious, though, if the go between machine can contact the remote, why can't the BS connect to the remote?