Two way communication question

[Peluso]

I made a comment about the long term worth of the new Dish 811 receiver in another forum and it got me thinking.

Ok, Here is the question: Would it be possible for a 921 media center like box to stream prerecorded HD content to 811 like box. This is sort of like the Moxi model, but it would be HD and the signal would be sent back over the coax to a central switch on or near the dish.

The way I see it, the 811 like box would not only have to do everything it's currently doing but it should also be able to see all of the recorded media on the 921 and be able get the media streamed in real time.

Since i'm not an engineer, I have some questions:

Is there enough bandwidth available on the coax cable?
What are the technical hurdles?
Could current equipment be modified to do this or does it have to be new product built from the ground up?
Would running Ethernet to each box be a better solution than trying to figure how to get high bandwidth going two way over household coax?

[boba]

The 921 should be recording the raw data stream for the channel selected so it should be technically feasable to have a 811 type receiver decode that information. Currently there is no output from a 921 just an output of processed information so it would currently be impractical but not impossible.

[ericha]

-There's plenty of bandwidth on the coax--there are already dozens of channels on it--what's one more? There may be some issues with the frequency assignments compared to what's already there, especially if you have OTA or cable duplexed in with the satellite signal.

-A significant hurdle is managing multiple data streams to & from the disk at HDTV rates. The 721 does this (2 streams on & 1 stream off) at SDTV rates, and does reasonably well, but when you are doing all three things, the user interface gets slow, and things don't always work so well.
Without more details, it's hard to say how big a job this is. If the output was only 1 stream at a time (i.e. you could watch the 811 or the 921 outputs, but not both), this wouldn't be a problem. But if you want to watch 2 streams, and record 2 streams at the same time, that could be a problem. The fix could be as simple as sharing bandwidth between disks, or as complex as changing the backplane architecture. This is a question that only the 921 hardware architect could really answer.

-Having a modem (MOdulator/DEModulator; this is a universal term, not just between your computer & dial-up network access) that can put out a HDTV stream isn't a big deal technically--the set-top boxes already have the receiver part, and that's far harder than the transmitter. However doing this at a low cost is far more difficult. Unless there is huge volume, no one will invest in creating chips to do this. At low rates it would be pretty simple, as you could use chips from a cable modem box (I think someone has already done this to get Ethernet over coax), but this is only 1 Mbps or so at best--far too slow for HDTV.

-A far simpler solution is to use 100BaseT Ethernet. This might be a bit slow--Ethernet has horrible overhead--the 100 Mbps raw rate is more like 20 Mbps usable rate, which might be just enough. 1000BaseT Ethernet is just becoming available at reasonable prices, and would certainly have more than enough bandwidth.

-Since we don't know the details of the 921 or 811 hardware, we can't say if they could be modified. It seems likely, however, that the hardware could be modified fairly simply, at least for adding the Ethernet interface. If the disk isn't fast enough to manage enough streams, this could be much harder.