Dave, thanks for that excellent historic perspective of some of the issues that were relevant at the time. I didn't want to get that granular with my initial response to the poster, but since you've brought it up I'd like to add a few observations and offer some clarifications at the same time.
While VoD over twisted pair delivery schemes was something that the open video system (OVS) guys were pushing from a progaming perspective back then, the actual technology that DSLs were forced to utilize was actually considered switched digital video, or SDV.
VoD, on the other hand, could utilize SDV, but VoD was only one of a number of layered or tiered side offerings which portended a kind of hierarchical storage and retrieval architecture, behind the scenes. It was SDV, however, that constituted the residence-to-headend (or central office, in this case) schema.
The reasons for SDV were obvious. A limited capacity twisted pair line, at best, could only deliver one full motion program grade service from the head end at any one time. This required a means for users to change their channel selection by sending commands all the way to the head end, and redirecting a different channel downstream every time they wanted to change a channel.
Traditional cable TV, in contrast, with its hundreds of MegaHertz delivery scheme could actually deliver the entire spectrum at once, and the selection process took place right at the set top box, without the need for upstream involvement.
Just a couple of clarifiers, which I hope you don't mind, to an otherwise excellent tutorial reply.
Regards, Frank Coluccio
ps - re: "To my knowledge, no such system has been implemented- "
Siemens Nixdorff implemented what they called FreeBee TV in some skyscraper multidwellings, about two years ago in NY City. It used SDV to deliver free TV to tenants, and it was paid for by advertising dollars. Not sure if it's still up and kicking, in the presence of RCNC and TWX pressures, but that is one early implementation that I was aware of at the time. I think I posted the details upstream somewhere in this thread at the time. |
