That document doesn’t say what layer. But it does say it supports Websockets.
Just odd that when I try to set it up using a named tunnel I don’t get an option to specify the WS service type. However it does require a service type if you want to connect to it.
Looking at this page it would seem that it’s a layer 7. Although I could be wrong, but my front end app has issues finding my backend service for websockets.
Granted I even tried to connect to my private computer using other protocols. I couldn’t get through. Anyway I’m most likely going to be taking that project offline soon.