It Struck Me Funny…

Last time, we discussed the fundamental delivery schemes being used in many telco-based IPTV installations.  To recap:

• By and large, telcos deliver broadband using some flavor of DSL.
• IP-based television being delivered over an xDSL infrastructure has implications for both the consumer and the provider.  Specifically, the available bandwidth on DSL tends to be limited, forcing certain technology decisions throughout the video delivery infrastructure.
• Unlike the traditional cable model, only the channels being watched are “on the wire” at the subscriber’s premise at any one time.
• Compression technologies are offering better ability to deliver more content, at a higher resolution.

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I won’t go into the hairy details about all this, but some description of how only the channels being watched are on the wire would be helpful.

IPTV relies heavily on the concept of multicasting.  Multicasting is a the middle-ground between the “one connection per subscriber, for any given channel” and “all subscribers get this channel”.  Let me explain.

In a “unicast” model, each subscriber would indicate to the IPTV system that they are interested in watching a given channel.  The system begins directing the video/audio content to that subscriber.  Simple.  Except that in this model, if another subscriber also wants to watch the same channel, another copy of that channel is put onto the wire, directed toward the second subscriber.  The problem here is that the content is duplicated and more bandwidth is used.  Regardless of whether or not each subscriber has their own dedicated DSL line to the provider, the back side of that is a single connection (to the DSLAM for example).  If every subscriber served by a given DSLAM wanted to watch the same channel at the same time, the unicast model would require that the content be duplicated for each.  This would consume an enourmous amount of bandwidth and would simply be impractical.

On the other end of the spectrum, each channel could be broadcast.  In this model, it wouldn’t matter if one or 1000 subscribers wanted to watch a given channel, it would be at least be present at the serving DSLAM.  Again this represents a huge network bandwidth penalty.  So, what exactly is the “middle of the road”.  Multicasting, to answer that question.

Multicasting (again in an abbreviated description) allows better use of network bandwidth by allowing only those who are interested in the same content to receive it.  For DSL, this indicates that the DSLAM will be receiving only one copy of the video and audio, sending that content only to the subscribers that are currently watching that channel.  If the DSLAM is serving 100 customers and only two are watching say, ESPN, then it will only receive a single copy of ESPN and will send that only to the customers watching it.  If no customers are currently watching ESPN, the DSLAM has the option of “unsubscribing” from the channel, freeing up bandwidth for other channels.  Note that there is a LOT going on here and also notice that much of this discussion centers around what’s happening at the DSLAM.  Since the DSLAM provides individual connections and bandwidth to each subscriber, it’s a great point to control what data goes where, with respect to the subscribers it serves.  Regardless, multicast allows the DSLAM (and other network elements) to limit bandwidth used to only that which is relevent at the time.  Without it, the network would get congested very quickly.

So, back to IPTV at the subscriber premise…

Let’s say you have an 18 Megabit connection on your DSL modem.  At first blush, that sounds pretty fast and so surely it move a lot of data.  However, if you look at the bit rates consumed by video you start to very quickly wonder if it’s enough.   Remember too that most of the time there’s more than video on the network.  You have your Internet connection using that same 18 Megabits.  That’s your Web browser, email client, game system, etc.  Now, consider that most households have more than one TV and that very often more than one are in use at a time.  Finally, remember that HDTV has become more and more popular and that HDTV takes much more bandwidth than standard definition television.  Still feel like 18 Megabits is a lot?  Lest you’re sticking to your guns thinking that’s a fat pipe, consider these facts:

• Using MPEG 2 encoding, getting a good quality standard definition TV channel consumes about 3.5-4 megabits per second.
• Using MPEG 2 encoding, getting a good quality 720p resolution high definition channel uses about 10 megabits per second.

So, if you’re watching ONE high definition TV channel at 720p resolution and one standard definition TV channel, you’re already using nearly 14 megabits per second!  Since there’s some overhead associated with a DSL channel (for our purposes, use 2 megabits/sec), you’re pretty close to the limit of what can be delivered on your DSL link.  Yeah, you still have about 2 Mbits/sec. for your Internet activities. What happens though if someone wants to watch a third channel or individual watching the standard definition channel decides to watch another high def channel?  Well, adding the third SD channel puts us over our limit, and changing the SD channel to an HD channel ups the ante’ by 6 Mbps, also pushing us over the edge.

So, there’s  a problem here wouldn’t you say?  What’s the answer?

There are really only two answers to this dilemma:

1. Increase the amount of available bandwidth.  Simply put: get a faster DSL line.  However, that’s not always possible and unless you get a pretty significant boost in bit-rate, the improvement to your situation may be marginal.
2. Make better use of the bandwidth you have.  This one makes sense for any situation, unless you somehow happen to have unlimited bandwidth.

To better use the bandwidth you have, you might take a few paths:

• Send the data for any given channel at a lower bit rate.  This can save bandwidth, but results in poor quality video.
• Somehow increase the compression of a given video/audio stream.

The latter option is where H.264 (AVC) MPEG 4 encoding begins to shine.  Notice that the bit rates I quoted for standard and high definition video were for MPEG 2 encoding.  MPEG 2 is a standard for video encoding that’s been around for a pretty long time and is well understood and well established.  It’s the basis for DVD video encoding, as well as for over-the-air digital TV (the move to all-digital television takes place on June 12, 2009).  However, its compression rates aren’t so good for IPTV as we’ve demonstrated.  When you consider the rapid move to HDTV, those compression rates aren’t really sufficient for DSL-delivered television, given the prevailing data rates.

H.264 achieves considerably higher compression rates for a given bit-rate, while maintaining good picture quality.  It’s nominally about 2x as efficient in its compression, resulting in a video channel of equivalent quality as MPEG 2, at about half the bit rate.  So, using the MPEG 4 compression rates, let’s do the same example as before:

• Using H.264 encoding, getting a good quality standard definition TV channel consumes about 1.75 – 2 megabits per second.
• Using H.264 encoding, getting a good quality 720p resolution high definition channel uses about 4-9 megabits per second.

You’ll notice that the numbers aren’t exactly half those of MPEG 2.  Experience shows that some variations occur and these are “thumbnail” ranges.  In any case,  let’s consider the things you can do with that extra bandwidth, in a more summarized form:

1 SD channel (480i) = 2 Mbps

1 720p HD channel = 7 Mbps

1 SD channel (480i) = 2 Mbps

…still at 11 Mbps of an available 16 (remember we’re assuming 2 Mbps overhead of our 18 Mbps).  We’ve already been able to add another SD channel and have .  Let’s keep going…

1 HD channel (720p) = 7 Mbps

1 HD channel (720p) = 7 Mbps

Now, we can watch 2 HD channels and still have 2 Mbps for Internet or even another SD channel.  Another thing to note here is that since most Internet activity is “best effort”, the visible effects on that kind of traffic can often be missed because the data being delivered are not time-sensitive.

All of this still demonstrates the squeeze we’re put in with the limits I’ve set for our example.  However, the 18 Mbps rate isn’t some hyperbolic example put out to show the extremes.  This is a common bit rate that can be delivered by the Telcos, using either ADSL2+ or VDSL2.  Both kinds can reach higher bit rates, but that usually comes at the cost of either decreased reliability or the need to get the DSLAM closer to the customer.  Generally, the further away from the DSLAM (or serving DSL line card), the lower the reliable bit rate.  Again, there are rules of thumb and other factors that play into all this, but the fact remains that it’s quite hard for many Telcos to provide bit rates at or above our hypothetical 18 Mpbs.  If you go with the 18 Mbps as a common bit rate, the examples show quite clearly the problems facing IPTV subscribers and providers alike.

Next time: What does this all mean?

Phone companies do.  At least any of those that don’t happen to be Verizon…

I mentioned in my previous post that “IPTV” as a technology for consumers isn’t all that important…from their perspective.  On the other hand, it’s a vital technology as competition for consumers’ communication dollars increases.

For years, the cable companies (and more recently, satellite providers) have been the principal sources for video content.  They’ve had control of both “live” (often referred to in IPTV vernacular as “linear TV”) and on-demand media.  When the Internet (specifically the World Wide Web) began to gain popularity, phone companies and video providers alike decided they needed to be there.  The cable folk had a largely analog pipe in the form of their coax infrastructure, while the Telcos had an enormous network of switched twisted-pair connections to virtually every home in the country.  Neither was truly prepared for the ‘Web.  Both saw an opportunity.  Both needed to upgrade their infrastructure to meet the demand.

Cable began the transition to a hybrid fiber-coax configuration and the Docsis standard, while Telcos began earnest development of a mechanism that provided digital transport while protecting their analog voice services, in the form of xDSL.  Both succeeded in building a basis for best-effort delivery of Internet data services. Consumers declared “It is good”.

“But wait!”  “Why should we stick with simple Internet service when with a little extra work, we can also provide voice service?”, asked the cable companies.  Why not do a bit more and provide the “triple play” of voice, video and data so that a consumer will be inclined to get all their communications services from one player?  With that, the cable folk began implementing voice services across their IP infrastructure in the form of VoIP.  Once they had this capability, they could offer it all in a nice package that a consumer would be motivated to purchase.  Hey, when you have a big pipe, you can offer lots of neat stuff.  Consumers declared “It is good”.

Phone companies began to sweat it.  They were only able to offer voice services and best-effort Internet data capabilities.  What to do now?  How to offer video to consumers that appears to be the same as traditional cable TV, except use that xDSL/IP infrastructure to deliver it?  Why not indeed?  Let me tell you why.

xDSL (ADSL, ADSL2+, V.SHDSL, VDSL, VDSL2, etc.) is a constraints-burdened solution for providing digital transport.  Given that the un-shielded, twisted pair architecture of the telephone system wasn’t designed for frequencies much above about 4 KHz, it’s pretty hard to push a high-bandwidth signal through a pipe as skinny as that.  The various flavors of DSL have been developed to push higher and higher speeds through that same skinny tube.  Still, the practical achievable data rates for DSL are limited.  In order for telco’s to be capable of providing what appears to be traditional video service, some restrictions had to be understood and dealt with:

• All the possible channels can’t be present “on the wire” at the same time.  This implies that a particular channel can only be delivered when the consumer wants it, unlike the old-style cable model where all channels are available at all television sets, all the time.
• Since many households watch more than one channel at a time, the effective bandwidth of the DSL delivery scheme has to be used in the most effective way possible so that all services can run simultaneously without interfering with each other.

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These constraints have driven the current structure of the IPTV services presently available.  Specifically:

• IPTV-based video services are designed to deliver only the channels currently being watched.  This saves bandwidth of the xDSL delivery.  Remember, there’s more going on here than just TV.  There’s Internet service, and sometimes VoIP (although that’s less popular with Telco’s just now).
• Video compression is used extensively in order to ensure that any given channel will use the least amount of bandwidth while maintaining the percieved quality of the video and audio.

What really helped the situation for the telco’s was the development of the H.264 (AVC) MPEG codec. It achieves extremely high compression rates while maintaining good video quality, compared to MPEG 2 compression at the same resolution/bit rates, etc.  This means a few things:

1. More channels can be on the wire at one time, translating to more people being able to watch different channels in the same household, at the same time.
2. High definition channels become more likely to be delivered.

There’s always a price to pay when you start squeezing more into less space and this is true for xDSL-delivered video.  Next time, we discuss the trade-offs and what this all means to both telco’s and consumers.

There’s been a fair amount of online chatter about the possibilities offered by IPTV.  I work in the Telecommunications industry and I can affirm the large-scale interest that Telco providers have in this technology. That said, I wonder if the discussion is a little off-focus.

First, a little bit of definition.

IPTV is often confused with Internet TV.  The distinction (from my perspective) is really that Internet TV is a more demand-oriented, ala carte’ group of offerings that includes content from potentially many sources (think YouTube, Hulu, your kid-sister’s teenage daughter, etc), delivered across the public Internet and most frequently accessed by a personal computer.  A lot of times, it can also be viewed on your TV’s by way of a computer-to-TV connection or some specialized kind of set-top box.  It can also be sourced by some aggregator of content so that it appears to be a unified set of services or it could be up to the user.  The primary discussion here is more about the “other” IPTV.  To me IPTV really more often refers to video service offered by a provider such as your cable or telephone company, in which:

• The content is not specifically delivered across the public Internet.
• The content is controlled by the provider, often this includes some assurance of better quality.
• The content is packaged by the provider, frequently much like traditional cable television’s different service tiers.
• The content tends to be more “traditional” (network providers like CBS, ESPN, etc.)
• Content is television-centric.

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Now I realize that these points aren’t definitive nor are they always all constituents of a given offering.  Still, the main difference is that today, “IPTV” tends to look more like what you’re used to from cable companies.  Note too that in both the “Internet TV” and “IPTV” cases, content is delivered using TCP/IP in some fashion.  That much is certainly common.  Still, it’s also interesting to note that when you hear the term “IPTV”, it’s frequently in the context of video services offered by your phone company (Verizon’s FIOS excluded, but that’s another topic).  The reason for this is fodder for another post.

So back to my title question: “Who cares about IPTV”?  I mentioned that the discussion about IPTV is kind of missing the point.  Why?  Mainly because I think for the most part that folks don’t really care how their content is delivered.  Why does it matter to them whether their video comes in on a coax cable or a twisted pair of wires?  Do people care if the delivery protocols are TCP/IP or Yiddish?  I don’t think so.  It’s very similar to how I feel about VoIP.  To a subscriber, what does it matter if their voice is going out in packetized form?

What I believe folks *do* care about is:

• Getting the content they care about
• The quality of that content
• The cost of that content
• The reliability of that content
• What they can do with that content (DVR, content portability, etc.)

If it’s true that people don’t fundamentally care about how their services are delivered, isn’t it time to focus the discussion of next-generation video services around the points above, and more?  What can be delivered to consumers that they haven’t been able to get traditionally and will those features be interesting enough to for them to pay for?  Should we be thinking about these services strictly in terms of entertainment, or should we begin to see the video interface as being useful for more?  Remember “convergence?  Think things like Apple’s “Apple TV”, a device that is evolving into a tool for more than simple video viewing.  Do people want that kind of integration?

I’d love it if someone would come out with something that I can say “I really gotta have that”, but it hasn’t happened yet.  I have Verizon FIOS and while it’s an excellent service, I still simply think of it as cable TV.  Maybe that’s how I should think about it and give up on expecting more.  (One point that has confused me since I got the FIOS video service: When you get FIOS data, your phone service is delivered using the FIOS optical transport.  This implies that if you have that and the FIOS TV service, the video part could be integrated with the telephone part to offer you things like on-screen caller ID.  Geez, my sister and brother-in-law have that with their cable service.  Why can’t FIOS subscribers?  For that matter, couldn’t that info be used to create smart answering systems that can be gotten to from your TV, PC, Internet mobile, etc.?)

So, for now I don’t have a lot of interest in “IPTV” from a consumer perspective, because I don’t think it matters much.  I certainly do from a business and technical direction, but that doesn’t help susbscribers.  I’ll have more to say on the subject in the next post.