Protocol Television (IPTV)
Over the last decade, the growth of satellite service, the rise of digital
cable, and the birth of HDTV have all left their mark on the television landscape.
Now, a new delivery method threatens to shake things up even more powerfully.
Internet Protocol Television (IPTV) has arrived, and backed by the deep pockets
of the telecommunications industry, it's poised to offer more interactivity and
bring a hefty dose of competition to the business of selling TV.
describes a system capable of receiving and displaying a video stream encoded
as a series of Internet Protocol packets. If you've ever watched a video clip
on your computer, you've used an IPTV system in its broadest sense. When most
people discuss IPTV, though, they're talking about watching traditional channels
on your television, where people demand a smooth, high-resolution, lag-free picture,
and it's the Telco's that are jumping headfirst into this market. Once known only
as phone companies, the Telco's now want to turn a "triple play" of
voice, data, and video that will retire the side and put them securely in the
batter's box. In this primer, we'll explain how IPTV works and what the future
holds for the technology. Though IP can (and will) be used to deliver video over
all sorts of networks, including cable systems.
How It Works
things first: the venerable set-top box, on its way out in the cable world, will
make resurgence in IPTV systems. The box will connect to the home DSL line and
is responsible for reassembling the packets into a coherent video stream and then
decoding the contents. Your computer could do the same job, but most people still
don't have an always-on PC sitting beside the TV, so the box will make a comeback.
Where will the box pull its picture from? To answer that question, let's start
at the source.
Most video enters the system
at the Telco's national head end, where network feeds are pulled from satellites
and encoded if necessary (often in MPEG-2, though H.264 and Windows Media are
also possibilities). The video stream is broken up into IP packets and dumped
into the Telco's core network, which is a massive IP network that handles all
sorts of other traffic (data, voice, etc.) in addition to the video. Here the
advantages of owning the entire network from stem to stern (as the Telco's do)
really come into play, since quality of service (QoS) tools can prioritize the
video traffic to prevent delay or fragmentation of the signal. Without control
of the network, this would be dicey, since QoS requests are not often recognized
between operators. With end-to-end control, the Telco's can guarantee enough bandwidth
for their signal at all times, which is key to providing the "just works"
reliability consumers have come to expect from their television sets.
video streams are received by a local office, which has the job of getting them
out to the folks on the couch. This office is the place that local content (such
as TV stations, advertising, and video on demand) is added to the mix, but it's
also the spot where the IPTV middleware is housed. This software stack handles
user authentication, channel change requests, billing, VoD requests, etc.-basically,
all of the boring but necessary infrastructure.
the channels in the lineup are multicast from the national headend to local offices
at the same time, but at the local office, a bottleneck becomes apparent. That
bottleneck is the local DSL loop, which has nowhere near the capacity to stream
all of the channels at once. Cable systems can do this, since their bandwidth
can be in the neighborhood of 4.5Gbps, but even the newest ADSL2+ technology tops
out at around 25Mbps (and this speed drops quickly as distance from the DSLAM
[DSL Access Multiplier] grows).
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