Please help me understand cable internet technology.
June 25, 2012 1:48 PM   Subscribe

Please help me understand cable technology. Why is it that my cable company can deliver hundreds of high quality TV channels but not an internet service that seems just as fast?

I can't get my head around the following observations:

1) Cable TV delivers hundreds of channels, including dozens in HD, with almost no hiccups. I even get live video broadcasts in very good quality. And while things have been getting better over time, it seems like cable has been "streaming" video to me for decades.

2) The same cable also provides my internet access. Only in the last couple years have websites like Netflix and Hulu been able to deliver something that can sorta compete with the video I get through cable TV. And live broadcasts via the internet are pathetic compared to what I can get on my TV.

Please help me understand what is going on here. I'm not sure exactly how to phrase my question, so I'll just throw out a few...

How is the capacity of the cable infrastructure divided between television and internet services?

Is there something fundamentally different about the data coming to me via the TV service versus the internet service?

If a cable company were to eliminate its TV offering, could it offer me dramatically faster internet service using the existing equipment/infrastructure?
posted by mullacc to Technology (11 answers total) 4 users marked this as a favorite
There are two things going on:

First, when your cable provider needs to provide the same exact stream to a few thousand customers, it can share the wires much more effectively than when it provides a free-flowing network stream to those customers. If a hundred customers are all watching the same TV show at the same time, they're all pulling down the signal for that one channel. If a hundred customers are all watching YouTube or Hulu slightly out of sync, that's a hundred different signals that need to go down some set of wires simultaneously.

Second, the cable company has no business reason to give a third party the ability to deliver to you what you want to watch when you want to watch it. They have lots of business dollar reasons to deliver contracted shows with commercials intact when and where the programmers decide, so solving the "why does my Hulu show stutter" isn't in their best short-term interest.
posted by straw at 2:05 PM on June 25, 2012 [1 favorite]

Watching television is like sitting in a theater listening to someone give a speech. There's only one person, on one stage, speaking into one microphone, and yet everyone in the audience can hear it--even the people who are bored out of their minds that are trying to sleep.

Now imagine if everyone in the theater decided to get up and individually ask the person on the stage to deliver the speech. And imagine if after every sentence of the speech, the person listening in said "uh huh" to let the speaker know that they had heard it. That's the Internet.
posted by RonButNotStupid at 2:12 PM on June 25, 2012 [2 favorites]

Best answer: There's a fixed amount of bandwidth that can be delivered on the coaxial cable. In a particular neighborhood, that cable is a shared medium: everyone's house gets the exact same signal. Out of everybody's cable jack, data is blasting through simultaneously for every single TV channel as well as the internet data for everybody in the neighborhood.

The big difference is that the TV bandwidth is shared: they can use up a certain percentage amount of their bandwidth sending out, say, NBC, and everyone in the neighborhood can get that signal and make use of it. With normal internet data, however, they have to allocate an amount of their bandwidth for each household, and you only get a little bit of it. Normally, each household gets an amount of bandwidth for their Internet equivalent to a single analog standard-def TV channel. There's something called DOCSIS 3.0 that lets you have multiple channels worth of bandwidth, but the plans that take advantage of that speed are very expensive.

straw also brings up an important point: cable companies make a lot more money selling TV than Internet, so it's in their interest to give short shrift to their Internet service by capping data and reducing bandwidth.
posted by zsazsa at 2:14 PM on June 25, 2012 [3 favorites]

Best answer: 1 gigabit/sec of TV delivered to 1000 homes == 1 gigabit/sec of load on the distribution network.

1 gigibit/sec of internet delivered to 1000 homes == 1000 gigibit/sec of load.

Because in the first case, all 1000 homes are receiving the same thing. In the second case, they're all different.

And it means the cable company has to have a 1000 gigibit/sec connection to an internet backbone, too. Whereas the TV comes to them via satellite dishes.
posted by Chocolate Pickle at 2:33 PM on June 25, 2012 [1 favorite]

Response by poster: zsazsa: your phrasing is starting to make sense to me. But let me see if I really understand it...let's say a neighborhood has 50 homes and the cable company has 50 channels. And each home is also allocated 1 channel-equivalent of internet bandwidth. That would mean the cable company is actually sending 100 "channels" worth of capacity to the neighborhood but each house only receives 51 channels worth.

And if the cable company eliminated TV services and re-allocated the bandwidth, each house would only double its internet bandwidth (100 channel-equivalents / 50 houses = 2 per house, compared to 1 in the prior example).


So assuming I'm on the right the cable companies' on-demand services act more like internet traffic than TV traffic? Or maybe something in-between if the data is hosted local rather than out on the net somewhere? I assume that content is NOT being streamed to everyone like a typical channel, but only delivered to a specific address when requested?
posted by mullacc at 2:41 PM on June 25, 2012

Best answer: On-demand service isn't "always on". What's happening with that is that a given area will have a certain number of TV-channel equivalents allocated to "always on", but far fewer than the number of custtomers. When someone orders an "on demand", they get allocated one of those channels for the duration of the program. Then it's freed up and can be used by someone else.

On Demand is a lot like cell phones: you get a dedicated channel, but only as long as you're using it (and paying for it).
posted by Chocolate Pickle at 2:52 PM on June 25, 2012 [1 favorite]

Some googling turned this up:
I work in the cable industry and spend a fair amount of time with Comcast. I do know a a bit about their On Demand network.

When you decide to watch a movie, your set top box (must be digital) sends a message to a video server located somewhere in your city. The server sets up a session with you set top box. A single digital TV stream (about 3.5 MB/s) is reserved for your use. Generally 10 or 11 of these streams fill a 6 MHz TV channel. This makes the On Demand system is a major user of network bandwidth. To allow any significant number of On Demand users, the network must be segmented -- different streams are sent to different geographical locations within the network at the same RF frequencies.

There are many more details. But this is a high-level overview of how the system works.
Which, on preview, fits with Chocolate Pickle's remarks.
posted by chazlarson at 2:54 PM on June 25, 2012 [1 favorite]

I screwed my comment up.

...certain number of TV-channels allocated to on-demand, but far fewer...

My apologies.
posted by Chocolate Pickle at 3:24 PM on June 25, 2012

(This is from my husband, a network engineer at a cable company.)

Keep in mind that adding more and more HD channels is quickly eating up the bandwidth upgrades that cable companies have been adding over the years. Adding a channel cuts off bandwith on the core network. Even with this though, they are staying ahead of the game. Many providers are delivering well over 10m speeds and that wasn't around more than a few years ago. They're constantly investing to keep up.

When you have service with a cable company, you're sharing bandwidth that the company has allocated to 10,000 or so of your neighbors. If a lot of people are on at once everyone slows down.

You're specific problem is coming from a higher demand for bandwidth. More people want things like Netflix and Hulu now. Cable companies are not presently allowed to throttle down traffic to sites like those so if many are streaming from them, access to other sites will slow down. Not that they should do that, it's just a variable they're dealing with.

Rather than getting worse, I think this is the kind of thing that will get better before it gets better.
posted by Madamina at 4:06 PM on June 25, 2012 [1 favorite]

Er... "your."
posted by Madamina at 4:07 PM on June 25, 2012

Best answer: Ok as previously stated your cable internet is essentially a broadcast channel worth of data, shared between everyone serviced by a single "node". Note when @home first started doing cable internet you were generally on the same subnet as your neighbors and if they misconfigured the network you could actually see your neighbors computers if you turned File and Printer sharing on. As more an more stuff is going over the internet pipes Cable operators are splitting nodes like crazy so where before you might be sharing the last mile of internet with 200 people, now it might be down to 100 people.

I assume that content is NOT being streamed to everyone like a typical channel, but only delivered to a specific address when requested?

No, exact opposite, a VOD stream is literally your own private channel using the same route as your broadcast channels. Actually technically anyone in your neighborhood could tune to this channel but you get a unique encryption key when the VOD session starts which only allows you to decode it. This is why companies like Comcast and Verizon are building apps for the Xbox which streams over your internet instead of using the traditional cable infrastructure its a much easier pipe to manage.

Why is Netflix not as good as your broadcast HD? A standard HD channel usually uses about 10-15Mbps of data. Netflix and Hulu's best streams are usually about 4-6Mbps of data streamed over your internet pipe (Sometimes smartly switching between different bandwidth streams in order to provide a smooth connection). While Netflix could provide higher bandwidth streams its not really efficient most folks can usually only stream via the internet at about 1.5Mbps. But Netflix and Hulu will get effected by other people's internet.

There's actually a trend in the industry to switch to Switched Digital Video. In this case everything is delivered like VOD where you get your own dedicated "channel". The downside here is that you don't share bandwidth for channels with your neighbors, the upside is that you can get almost an unlimited channel lineup because the channel switching actually occurs at the cable head end instead of in the cable box.
posted by bitdamaged at 5:28 PM on June 25, 2012

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