K PattersonPremium,MVM
join:2006-03-12
Columbus, OH
kudos:1 | reply to insomniac84
Re: lol All channels are sent to the neighborhood hub, not to the node.
The hub (which, incidentally, is where the CMTS's are located) sends them to each of the several dozen nodes it supports as required, and tells the set-top box how to tune to the program.
The next step, once the copyright issues have been resolved, is to allow users to "record" the program at hub. In other words, a DVR without anything more than a set-top box at the residence. |
approval from:
fAcEtIOUs 
| Actually it is to the service group, which is a logical collection of nodes. That is not, strictly speaking, equivalent to the hub.
SDV relies on queueing theory just like the phone company does to allow more tuners to be connected to the network than there are "slots" to serve them. It' sort of like how there are more phones than dial tone available at the CO.
When a cable system has SDV, there are two species of video: the traditional broadcast channels and those that are in the switched pool. (Broadcast in this context does not mean over-the-air, it means traditional transmission of cable video channels). If you tune to a traditional broadcast channel everything works the same as before. If you tune to a switched pool channel, your tuner first looks to see if any other tuner in it's service group has requested it. If so, it just tunes to the temporarily assigned location of that channel and you're done. If not, it makes a request to the system to have that channel added to one of the temporary channels and it tunes to it.
It all happens very quickly in most cases, so the user cannot tell when they tune to a switched channel.
Niche Content and High Use Content...
The theory goes you should be able to switch your lowest viewed content since the chances of people watching very many of them at any one time in any one service group are low. You should also be able to switch your very highest viewed content since (and this will sound counter-intuitive) there are not that many of them and a very large number of people will tune to it. Remember that if any one tuner calls for a channel, all the other tuners can tune to that temporary feed without taking up any more slots. What makes it all come together is the fact that when highest viewed content is on and the most number of tuners are in use, that usage is concentrated, so you don't run out of slots. When things slow down and viewership spreads up and down the dial (mid day, over night), the variety goes up but the overall number of turners requesting channels goes down.
Over time, the goal is to reduce the homes per node and nodes per service group and to increase the size of the "bank" of channels such that there is a one-to-one ratio between tuners and slots. That is called switched unicast. And that, my friends, is the day that the cable plant becomes logically limitless in terms of video capacity.
What makes this tricky is the space for the slots is not free. Each slot takes up the same space as a broadcast digital or HD channel. So at first, SVD eats bandwidth until a cross-over point is reached where you have placed more channels into the switched pool than you have used up with SDV slots. Depending on how deep you go, you can gain a LOT of bandwidth for use as additional SDV slots (so you can launch more digital and HD content) and for other applications. Typically groups of slots are launched a QAM at a time, so you will migrate chunks of content over time.
SDV, going all digital and upgrading to 1Ghz are the three primary levers cable operators have to stay competitive with the dish and the telcos. |
