In an earlier blog post I attempted to distinguish TVoIP (TV over internet) with IPTV, a buzzword for cable/telco live video offerings. My goal was to explain that we can be very happy with TV, movies and video that come to us over the internet after some delay.

The two terms aren't really very explanatory, so now I suggested VAD, for Video-after-demand. Tivo and Netflix have taught us that people are quite satisifed if they pick their viewing choices in advance, and then later -- sometimes weeks or months later -- get the chance to view them. The key is that when they sit down to watch something, they have a nice selection of choices they actually want to see.

The video on demand dream is to give you complete live access to all the video in the world that's available. Click it and watch it now. It's a great dream, but it's an expensive one. It needs fast links with dedicated bandwidth. If your movie viewing is using 4 of your 6 megabits, somebody else in the house can't use those megabits for web surfing or other interactive needs.

With VaD you don't need much in your link. In fact, you can download shows that you don't have the ability to watch live at all, or get them at higher quality. You just have to wait. Not staring at a download bar, of course, nobody likes that, but wait until a later watching session, just as you do when you pick programs to record on a PVR like the Tivo.

I said these things before, but the VaD vision is remarkably satisfying and costs vastly less, both to the consumer, and those building out the networks. It can be combined with IP multicasting (someday) to even be tremendously efficient. (Multicasting can be used for streaming but if packets are lost you have only a limited time to recover them based on how big your buffer is.)