Automatic Upload Of Data To A Webserver Database?

I have a question what's the best way to accomplish the following task:

- I have an ASP.NET application with SQL server database (hosted externally at any provider)

- There are a few dedicated client computers anywhere in the world and these client computers shall run a periodic automatic process to upload some data into the database of the webserver. So there is NO user in front of those computers to open a browser and run any kind of upload manually. (These automatic processes are not part of my question, they can be windows services or simply running applications on the desktop.)

My initial idea was to use FTP for this purpose, means: Those perodic processes on the specific clients create files and put these files via FTP in any defined folder of the web server.

But what follows then? Is it possible to have any eternally running process on the web server to process those uploaded files in the FTP folder and write their content into the database? As far as I understood until now an ASP.NET application has sessions and an application process but a session shuts down as soon as the associated client doesn't send a request for some time and even the application process shuts down when no user at all sends a request for a specific time. Isn't it? So in other words: When no user sends any requests via HTTP my application on the webserver is simply not running and therefore cannot process the FTP-uploaded files. (Or can I keep the application "artificially" alive to run a peridic lookup for new files ???)

The other option I had in mind is to program a piece of software running as a windows service which could pick up the FTP-uploaded files and process them. But I have to consider that possibly the hosting company does not allow to install any service programs on their servers aside from the ASP.NET application. So this is probably not a real option.

And now my third idea is to develop an ASP.NET web service which runs on the same web server as the ASP.NET application. The specific clients mentioned above would connect to this web service via HTTP, upload the data and the web service would immediately process the data and write them into the database.

At the moment only the last option seems to be the "most natural" (and perhaps even the only possible ?) way to me. Are there any other options and methods for my purpose? And if so, what is the recommended way?