Cable Company Short On Bandwidth? - SDV To The Rescue

[57]

To clarify.

1. All channels are sent as far as the node, since there is plenty of bandwidth to the node (fibre).

2. The "last mile" is where the bottleneck is and where SDV comes into play. The people on that node may be watching only 100 different channels, so you don't need to send 400-500 channels to all those homes. This frees up all that bandwidth (relating to the unused channels). Each STB sends a request to the node for the channel desired and that channel is then sent to that customer.

3. There would be no channels "unavailable" and certainly not a popular one. There is a theoretical possibility that the homes could request more than a certain number of channels, however, studies would have been done on how homes in a node react and the variability in the number of requests may be from say 50 to 150 channels, but not 500 channels for example.

[james99]

So, what exactly is a node in this context? Is it the actually cable box you see along the street that usually feeds 1/2 dozen houses or is it something that feeds those boxes or do they currently exist at all?

[jvincent]

They definitely exist. There is a major distribution box at the end of my street that feeds most of the area, probably a few thousand houses.

I'd guess that it gets a fibre feed from the main Rogers head end. Depending on what else it feeds it probably uses a mix of fibre and coax for those.

Amusing anecdote, when we had the ice storm a few years ago this was the box that they brought a generator in to provide power to.

[Northcountry]

The best way to think of SDV is to think of it as VOD. The specialty channels that have low viewership get put on the SDV tier and when someone wants to watch that channel and tunes to it the channel gets served to that subscriber. Then if another person in that same service area tunes the channel they will also get served that same feed.
VOD is directed to a single customers for only that customers use. SDV is directed to a service area (node) and once being served is available for all subscribers on that node to use. You can't pause/ff/rew a SDV channel (unless you have a PVR), where as a VOD channel you can pause etc.

So bandwidth savings are only for the channels that the cable company decides to switch. For example if a they are currently putting 10 digital channels per channel bandwidth (6Mhz) and they decide to SDV 20 of those channels then they would free up 2 6Mhz slots...but they would require 1 of those slots for the SDV stream hence the 50% BW saving.
I think I got that right

[wh33lman]

A node in this context is the optical node in your neighborhood area. Optical nodes are placed to feed up to approximately 2000 homes. They are fed by fibre-optic cable from the local main hubsite, and they output RF signals on coax cable to your home. Generally every large town has a single hubsite..from Scarborough to Mississauga, there are several.

RF signals weaken with distance and frequency. To travel more than 1000ft from the optical node, they have to be re-amplified. To power those amplifiers, step-down transformers are installed to convert 120V line voltage to 60V or 90V. This 90V 60Hz "signal" is injected into the coax and travels along with the RF signals (50-1000Mhz) to the amplifiers.

Installed with the step down transformers (power supplies) are numerous batteries to keep the node and amps working in case of power failures. Due to the phone system requirements, 4 hours of battery life is planned. After 2 hours on batteries, a generator truck is sent to the power supply just in case. This is what Jvincent saw happening.

Now...for large systems, those local hubsites are interconnected by large capacity high-speed network backbones. Channels and services are placed on these backbones and dropped off at the hubsites as they move around the network.

For SDV, certain channels (basic services and most popular channels) are always placed on the backbone and sent out to all the sites and nodes. Any one of the remaining channels will be only put on the backbone if a customer selects that program. The program will be dropped off at the hubsite, assigned to a modulator that feeds your node, and sent out to you. If another customer fed off the same node requests the program, he will be tuned to the same stream as the first customer.

If another hubsite has a request for the program, the channel will be picked from the same backbone channel. When no one is selecting the program it is removed from the backbone network.

[technut]

Thanks for the informative post wh33lman.

[I_Want_My_HDTV]

2. The "last mile" is where the bottleneck is ...

Actually, the last mile is causing a bottleneck on the main feed. That is why they are being converted to optical. The problem is that cable companies want to sell PPV and similar individual services. The last mile can handle that. The issue is that 5,000 or even 500 PPV requests can't be sent out on a trunk coax that already carries 400 conventional channels. If those requests are split up by neighborhood equipment accessing fiber optic trunk lines, coax can handle the last mile easily.

[technut]

You're both right about the bottleneck.. if the backbone isn't fibre yet, then it is the bottleneck. But once the backbone is upgraded then the last mile coax becomes the bottleneck.

But it's a pretty big neck... plenty of bandwidth to deliver what the customer wants... the problem is that it has also been delivering lots of stuff the customer doesn't want (eg. all the channels they aren't currently watching). Once that is minimized or eliminated there is a ton of bandwidth left available on the coax.

[Walter Dnes]

A "Devil's Advocate" type question here. Joe Blow gets a new TV set and decides to do a "scan" on his cable channels. What does that do to SDV? Or what about one of those nights "there's nothing on", and he decides to do some "channel surfing"?

[57]

Doesn't work without two-way communication and a compatible STB. Since most of the channels on digital cable are encrypted, "Joe Blow" would basically get nothing, or next to nothing, now anyway. Same for the current crop of CableCARD in the US, since they are not two-way. Some Cable companies have trials in the US and those with CableCARD are out of luck.

http://www.digitalhome.ca/forum/showthread.php?t=32271 QAM

True channel surfing is very slow these days - taking 2+ seconds for each digital channel, sometimes longer with format changes - better to bring up the IPG and see what's on and switch to the channel that way.

Each step is taking us closer to what will ultimately be every programme "on demand".

[57]

I read in the Globe this morning in an article regarding Superchannel that:

...Rogers said yesterday that it will offer the two HD channels once it introduces switch-digital technology that opens up more space.

http://www.theglobeandmail.com/servl...ry/Technology/

I'm guessing that SDV is closer than we think?

[travisc]

They said not so long ago that it was coming in 2008 - it's 2008, so hopefully they'll stick to that.

[Wayne]

This thread has not had a post in over 6 months - any update on when SDV is coming to Rogers?

One thing I haven't seen discussed in detail in this post - will tuning into an SDV channel be the same as tuning into channels today? Will you just enter the channel number and then the channel will tune in pretty much immediately? As opposed to VoD channels where you have an interminable delay and other interaction is required.

[thenewdc]

Supposedly their is no difference in the time it takes to tune any other digital channel as with SDV, very quick. Although your DTV box must be 2-way. If your VOD is working then SDV will be working.

[SensualPoet]

I'm guessing it's coming soon. If you Google about, you'll find references in late July to Rogers and Cisco striking an arrangement for equipment. My understanding is SDV works in the head end transparently for the customer so the upgrades all take place before the signals leave for your home. It allows Rogers to deliver more HD and even more niche SD channels than ever before using the existing fibre-coax network.

There's a press release here: http://newsroom.cisco.com/dlls/2008/prod_062608b.html