Switched digital video, is a partially IP based system that doesn't have the full range of video carriers coming to your local box or TV.
You will be reaching out to a server somewhere in your area, it has the advantage of not having all the video carriers, but it has a lag when changing channels (hopefully you don't channel surf it may drive you nuts, very slow).
There are many other differences when comparing a video based system with the switched digital video system, if you are really interested I can point you to some technical info.