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Comcast ON DEMAND
- Thread starter Jassi
- Start date
Matthias99
Diamond Member
Basically, it works the same way as a cable modem -- a chunk of bandwidth on the line is set aside for you, and you (or rather, your cable box) can request that a particular data stream is sent over that bandwidth chunk to your TV.
I would guess that bandwidth for ON-DEMAND is allocated dynamically, but this may not be the case. I don't know much about the actual implementation details of Comcast's network.
I would guess that bandwidth for ON-DEMAND is allocated dynamically, but this may not be the case. I don't know much about the actual implementation details of Comcast's network.
complacent
Banned
Why do you find it so humorous?
complacent
Banned
Is that true reddem0n? Do you have to let us all know how smart you are? How about you explain it to us, in detail, so we all know. Please cite any sources you use. Also, how about you give us an idea of what a good question is.
We could make fun of you for asking "Is there any spyware scanner out there to scan external slave hard drives? " THAT is a stupid question if I ever heard one. Anyone who has used a spyware scanner should know you can pick the drive...
How about "Friend of mine is interested in overclocking his card but really not sure on howabout going into doing this.. " A friend huh? SUUUURRRRE... And you couldn't answer this trivial question?
How about this question you asked "i posted something in the sale/trade forums and they said i better enable my profile how do i do this?" You couldn't read an FAQ? Just about any idiot can look this up...
Yet you ridicule someone in a forum that invites questions about how things work. I would say that you need to relenquish your ATOT account. You are clearly an idiot.
Matthias99
Diamond Member
Were you looking for something more detailed than my answer above? Essentially it works like a cable modem at the hardware level; I'm pretty sure HowStuffWorks.com has an article on those.
But think of the traffic generated this way and this traffic has to compete with cable internet connections and digital channels being carried over the same line. That is a lot of stuff to worry about. Also, think of how people can pause, rewind or ff. That's gotta be taxing on their resources. So, I think there is a better way but either people don't know (proprietary) or the right person hasn't walked in here yet.
Matthias99
Diamond Member
And? From their perspective, it's no different than another cable modem, except it uses a fixed (and relatively constant) amount of bandwidth -- and it's almost totally unidirectional. They have to deal with this problem already.
Well, you need a server on the other end to host the videos, but it doesn't take any more bandwidth to support ff/rewind -- and 'paused' video takes no bandwidth at all!
The Boston Dangler
Lifer
Allow me:
1) Video-on-demand content is stored in a server farm with zillions of hard drives.
2) Listings are transmitted to your DCT (digital cable box) on their own bandwidth. There's no "competing" for space, it's all allotted and controlled.
Specifically, the VOD barker is 1 stream on 1 channel with 265 QAM. That means 1 6-MHz channel carries 10-12 NTSC (regular def) or 2 maybe 3 ATSC (high def). The show will be on it's own channel and stream when you order it.
3) You hit the order button. The box talks back to the HEC (head end controller), and asks for the show. Billing systems are notified too.
4) The HEC calls the server farm, and the Teletubbies or whatever is sent over gigabit ethernet (fiber) to a reciever in the headend, then inserted onto the forward signal, where your box recieves it.
5) Data is encrypted, and only your box decodes your order.
6) All info is streamed at all times. That's why FF/REW is laggy compared to true PVR.
This is how cable companies do it.
1) Video-on-demand content is stored in a server farm with zillions of hard drives.
2) Listings are transmitted to your DCT (digital cable box) on their own bandwidth. There's no "competing" for space, it's all allotted and controlled.
Specifically, the VOD barker is 1 stream on 1 channel with 265 QAM. That means 1 6-MHz channel carries 10-12 NTSC (regular def) or 2 maybe 3 ATSC (high def). The show will be on it's own channel and stream when you order it.
3) You hit the order button. The box talks back to the HEC (head end controller), and asks for the show. Billing systems are notified too.
4) The HEC calls the server farm, and the Teletubbies or whatever is sent over gigabit ethernet (fiber) to a reciever in the headend, then inserted onto the forward signal, where your box recieves it.
5) Data is encrypted, and only your box decodes your order.
6) All info is streamed at all times. That's why FF/REW is laggy compared to true PVR.
This is how cable companies do it.
bpatters69
Senior member
All I can say is bye-bye Blockbuster..... sooooo soorry to see you go.
The Boston Dangler
Lifer
Well, it's not INSTANT, like a DVD player. Usually less than a second between hitting "pause", and the show stopping.
What is really going to be cool is MS IPTV.....of course that is of it gets off the ground......
http://www.microsoft.com/tv/content/Solutions/IPTV/mstv_IPTV_Overview.mspx
i read about it a year ago in a mag....not sure what its doing now.....
http://www.microsoft.com/tv/content/Solutions/IPTV/mstv_IPTV_Overview.mspx
i read about it a year ago in a mag....not sure what its doing now.....
Jeff7
Lifer
I think that was the one big part that we were all wondering about. One movie can take up several gigabytes; multiple movies, and entire series stored on hard drives? That's a damn lot of hard drives. Just seemed like it'd be prohibitively expensive. But I guess if you buy a pallet full of hard drives, it might be cheaper. 🙂
daniel1113
Diamond Member
What a beautiful sight that would be... a pallet full of HDs.
imported_Phil
Diamond Member
Indeed 😉
If I go downstairs right now, I get to see a hundred or so. Not enough.
Anyway, this is all highly interesting - roughly how much space would a cable-on-demand-ready movie or show take up? I'm going to assume that they use a high-ish quality codec to encode all the video, something that produces sizes similar to DivX maybe?
Matthias99
Diamond Member
DVD-quality SD video is ~6-9Mbps using MPEG2. MPEG4/DivX is somewhat more efficient... maybe 4-7Mbps for basically the same quality. Of course, they're probably compressing it further than that. At 6-7Mbps, you're talking ~3GB/hour. Keep in mind there aren't commercials, so a "one hour" show is only about 45 minutes long.
HD feeds are usually in the 15-20Mbps range, depending on the exact program. That would be somewhere from 6-10GB/hour of video.
Hard drive space, in bulk, costs maybe $.40/GB. They're probably using some sort of SAN solution where the cost is more like a few bucks a gig (with several TB of storage), but even that's pretty cheap to a huge company like Comcast.
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