Problem with router or internet?

Question

WiFi

There is a Rostelecom router 1W4L1USBn.
It has a TV connected to it. 2-3 computers, 2 phones work on wifi.
The problem is that very often the Internet slows down, tupits or stops working. TV in most cases works without failures.
How to determine the problem in the Internet or router? If in a router, then what to take as a replacement?

Answer 1

At Rostelecom (at least in my city), the Internet often lags, regardless of the router model. The provider is like this.
But first, of course, conduct an experiment with another router.