The downlink of digital TV is broadcast by HFC. If it is on-demand, you need to load the Cable Modem and get through the reverse return signal through CM. When you make an on-demand request, your CM will send an IP on-demand signaling back to the background on-demand platform, and then push down the on-demand stream through HFC network QAM. That is, IP is used for the uplink and HFC is used for the downlink.
In the future, after NGB (Next Generation Broadcasting Network) is covered, there may be cases where both uplink and downlink are IP, but it is still only piloted in some cities.
If you have anything to ask, you can keep asking.