Switched Digital Video (SDV) is rapidly gaining recognition as the best way to squeeze additional bandwidth out of a cable system.

http://en.wikipedia.org/wiki/Switched_video New Link

http://electronics.howstuffworks.com/switched-digital-video.htm Additional New Link

SDV is a pretty sweet technology. We've got a number of SDV systems up and running in our lab.

Of course, if you want to guarantee that the channel you want to watch will have a spot available on the QAM, you might want to leave a box or two tuned to it all the time! :)

57 doesn't start too many threads so it's a good idea to pay attention when he does :D

This sort of technology (along with the technology that converts digital to analogue) has been mentioned several times in the past.

Glad to see something may come of this, one day.

The article raised one point that I'm not sure I agree with.

It talked about how in the fully intelligent scenario that when I select ABC the "network" would know that I subscribe to HD service and would automatically give me the HD feed. What if I don't want the HD feed? There are cases now where I specifically tune to the SD feed because the HD is bad.

Personally, I'm not sure I see SDV as an enabler for general broadcast, but more so for PPV or VOD. Probably the biggest gains are to be had by MPEG-4.

Personally, I'm not sure I see SDV as an enabler for general broadcast, but more so for PPV or VOD.

SDV is definately suitable for general broadcast. In fact, it is already in use in a number of MSO headends in the US. However, you will probably notice that the majority of channels that are put onto the SDV infrastructure will be niche channels with lower viewership numbers. Further, as you build out your SDV system, you cluster your edge QAMs out into local switching hubs rather than at a central location. That way, for example, someone in London can watch GSN on the same QAM Freq/MPG# that is being used to stream Showcase Action in Woodstock. Same Resource Manager up in the headend but different physical QAMs.

As for the concern over getting the HD content when you want the SD, that's a ways off yet. Currently, the SDV streams are still mapped to a "traditional" channel map so selecting ABC-SD won't give you ABC-HD. But I understand the concern and I'm sure it will be addressed by the time the next phase of SDV hardware/software is being deployed.

Has anyone considered the privacy implications of such a technology?

Now the cable company knows what channel I'm watching at any given time.

Also, they could take this a step further and allocate more bandwidth to channels with the highest viewership, so people who have a preference for less popular programs will always suffer high compression artifacts and poor PQ.

1. The cable company already knows what channel you're watching if you have a digital terminal. They have stated that they do not pass this information on to others.

2. As you say, they can use this information to provide a better signal for some channels, however, the purpose of SDV is to give you a signal better than what you have now because the bandwidth that is currently "wasted" will be going into actual viewership.

This is a new technology which is only being rolled out in controlled trials in the US. At a high conceptual level, it's a great idea -- but it will take some time (2, 3, 4 years?) to be proven in the field.

Rogers has built its plant out to 860 MHz across most of Ontario -- well ahead of the peak 750 MHz in much of the US (and a lot less in many markets). Ultimately, it means Rogers has a significant amount of extra headroom for more HD and more diversity in SD channels -- like Great Wall Chinese language packages in the GTA.

If switched video doubles capacity on the same network infrastucture -- a reasonable baseline -- that's a great thing. That's a LOT of potential HD and On Demand programming that neither satellite nor IPTV over VDSL can hope to deliver. Rogers is in that position due to strategic investments in past years but it still remains to be seen if they will roll out this technology.

I already get (potentially) close to 500 channels with Rogers -- how many more do I need? I certainly want more HD (and less SD) ... but I am content to see HD grow as programming actually becomes available (I don't need more A&E and The Score in "HD").

Rogers offers me MORE than satellite can today. Will Bell bring IPTV to my doorstep? Eventually, yes -- but not yet. And in 2008 or 2009 or 2010 when Bell is ready to offer me a viable alternative to my 2007 TV experience, isn't it realistic to think Rogers will be offering me something significantly more? I can vouch that 2007 TV is way ahead of 2004 TV from Rogers.

Switched video is one arrow in the quiver -- and potentially a satellite and IPTV killer. Time will tell. I am confident that whatever transpires, Rogers will not blink. I'll have a leading edge TV experience available from Rogers even as the competitors, and industry, evolves.

SDV won't kill IPTV, since IPTV works at the fundamental level that SDV does, in providing only the channel(s) one selects to tune over the connection.

Ah, but if the only advantage IPTV has over Cable is SDV-like capabilities (not certain this is the only advantage, but I don't know a lot about IPTV services either), then maybe SDV will kill off IPTV...

It's a fine point but my understanding is SDV deliver SOME of the channels ALL of the time to your digital box. So everything gets to the neighbourhood node and some portion -- 50%? -- passes straight through to your box, and your neighbour's box. But that effectively frees up half the coax pipe leaving lots of room for On Demand choices or other niche regular channels.

Meanwhile, the node is connected to the head end via fibre and effectively has "unlimited" capacity.

IPTV works the same way except the copper telephone wire from the node to the home can only handle three or four SD channels at most. If you have a two-tuner HD PVR you're out of luck -- until this technology can drive significantly more bandwidth in the "last mile". Fibre right to the home would work but that remains, currently, prohibitively expensive. Cablecos and Telcos are in the business to make a profit so any new roll outs will have to be measured, or much cheaper.

When Rogers upgraded SARA on the terminals earlier in the year, some new diagnostic pages relating to SDV appeared, so our current terminals definitely support it.

This might be the "killer app" for phone companies. Currently, this is exclusive to Verizon in the US, but hopefully they will sub-license it up in Canada. I've heard great things about it like faster internet speeds, unlimited bandwidth for TV especially HDTV, and phone service of course.

http://en.wikipedia.org/wiki/Fios I think at&t has something like it as well.

This is the solution for both cable and IPTV providers. It essentially provides full bandwidth up to the last "mile" and limited, requested bandwidth for the final link. The advantage goes to cable since it already has the last mile in place and provides much greater bandwidth for that connection. IPTV is some years off with implementation and cannot provide the bandwidth of cable.

OK, I was thinking about this.

When the telcos have full fiber optic to your house, there will be full bandwidth. But you're right about the time. The wiki above says 10 years and fiber will fully compete with cable. I might get this when it comes to my area but by then, the bugs discussed on other sites will have been ironed out.

When the telcos have full fiber optic to your house

I wouldn't hold your breath for this. The cost of pulling fiber to everyone's house is enormous and the telcos won't do it until they are guarateed to be able to recoup their investment.

The only place you see it now is in a few newer "showcase" communities.

Bell is not planning to put fiber into residences. They are going to use DSL, which currently maxes out at about 25 Mb/s. New technology may extend that to 60 Mb/s in a few years. That is much, much less than cable, which currently has a bandwidth of about 900 Mb/s uncompressed and about 6 times that (5 Gb/s compressed with 256QAM.) Bell has a lot of work to do on their system before they can deliver HDTV, VOD and internet simultaneously over DSL. Cable is currently doing that in many areas.

In fact Bell's VSDL (ExpressVu TV for Condos) does not yet reach the 26 mbps but is expected to when they get around to releasing VDSL2 upon which platform they will run IPTV. This is the AT&T U-Verse model (which is, now, finally a product and not a trial). The current VDSL edition maxes out at about half this bandwidth -- hence the 3 TV stream + 1 3-mbps Internet feed max spec. And, as an HDTV stream under MPEG-2 requires around the entire bandwidth (13 mbps approx), Bell's hands are tied.

MTS TV in Winnipeg gets around these limitations by using a separate set of twisted pair copper for its one HDTV stream.

See also:

http://www.digitalhome.ca/forum/showthread.php?t=64860

There's also some decent background on SDV here at Light Reading:
http://www.lightreading.com/document.asp?doc_id=125584&site=cdn