Sorry, SDV is an abbreviation for Switch Digital Video, which is what bandwidth-starved cable companies implement to re-use frequencies in order to fit more channels on their infrastructure:
http://en.wikipedia.org/wiki/Switched_video
In my limited experience with it on my local Time Warner Cable outfit, it is poorly implemented, especially with Cable Card devices like Tivo.
I am amazed at how much more people on this site know than me. I have a long ways to go. Thanks for helping to educate me.