I am not sure of the bandwidth, but I'm imagining a wideband (almost CDMA-like for fellow cell phone junkies) system, where DirecTV can send a huge swath of data out over 20 or so TPs. Say a couple gigs per second--this would be an encoded stream of ALL of their on-demand content in packets in one wide channel, constantly looping. Furthermore, because it is not "real time", there could be less error correction and higher compression for similar picture quality.
If there is a control channel that has a "directory" of this data, then it is a matter of a receiver getting a request to download, say Pawn Stars, learning that it is in the data stream on Transponder 2, then beginning to collect the bits for that program out of the stream being sent down. Depending on how many programs are in each channel, their duration, compression, error correction would set how long it would take the program to begin downloading and finish buffering.
Again, I have no idea how feasible that would be--but it seems like it would make the most sense, and how they could possibly offer an "on demand" solution with a one-way system. Question is of course, if this is the path they are taking, would the current crop of DVRs have that sort of processing power? Would 20 Transponders be enough to carry everything they currently have on demand, if it was all constantly looped in a data stream?
I could see that actually working if the top programs are pre-buffered in the middle of the night (sitting on the hard drive, ready to go), and the less popular programs take less than 10 minutes to go from "pending" to "ready to view".In fact if the top programs are downloaded each night, then that is one less thing that could be part of the data stream during the day--just thinking out loud.
--Nat