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[ NNSquad ] Cable, TCP/IP, and Convergence

An NNSquad reader took issue with my posting earlier today where I
said that "digital cable is of course already (MPEG) TCP/IP."

Technically he has a point -- depending on which layers of modern
cable systems we're looking at.  Since the rapid advancing of this
technology is quickly blurring lines -- I would assert that in the end
making some aspects of these differences inconsequential from a policy
standpoint -- let's spend a couple of minutes reviewing, in simplified
form, how cable systems work and how this relates to our issues of
concern.  This may be more about cable than you ever wanted to know.

Traditional analog cable (or the fully analog channels of a partly
digital cable plant) is pretty easy.  Analog modulation, fixed width
analog channels, analog demod, processing, display.  Done.

Digital cable uses more advanced modulation techniques to fit multiple
digital (for example, standard definition) channels as (usually)
MPEG-2 streams into the space otherwise taken up by a single analog
channel, often using crypto and imposing various access rights (DRM -
e.g., CCI byte) along the way.  Cable systems would likely migrate to
MPEG-4 if possible due to bandwidth savings, but the massive installed
base of MPEG-2 equipment suggests that this will take significant

So far, this is pretty much a digital version of analog channels.  All
channels stream toward all users, all of the time.  On an
appropriately provisioned 2-way physical plant, DOCSIS can be used to
arbitrarily assign some portion of digital capacity (e.g. 256 QAM
modulation) to Internet access services.

Back to those ordinary MPEG video streams.  Since they're all
streaming at once toward all users, no real interaction is required to
view them.  But this changes when you introduce Pay Per View (PPV),
Video on Demand (VOD), or centralized DVR services, all of which
require more control by users (particularly the latter two).

Another aspect where more control is required is the rapid deployment
of Switched Digital Video (SDV) by cable companies.  SDV avoids the
need of sending all streams to everyone all the time, instead sending
less heavily viewed streams to particular neighborhood nodes
(typically N-thousand subs each) *only* when someone on that node
tunes to one of those channels.  As you can imagine, the "command and
control" aspects of this can be complex, as are interesting issues of
deciding when to timeout channels that you suspect are no longer being
viewed (or recorded).

TCP/IP is heavily used for these control and management functions and
is now essential for these systems to operate.

Meanwhile there is a clear push toward the deployment of fully
TCP/IP-based systems in advanced cable environments, in parallel with
experimentation with MPEG-4 compression.  The advantages of this sort
of convergence are obvious -- but again, there's a lot of already
deployed equipment to deal with, some of which (like advanced
downloaded-firmware java-based set-top MPEG-2 boxes) have only been out
in subscriber homes for relatively brief periods of time in many
systems.  So some of these changes may come comparatively slowly.

This is all interesting from a technical standpoint, but ultimately
has little to offer from a *policy* point of view.  A key policy issue of
note is that ISPs (whether cable, DSL, or whatever) are usually in a
position to unilaterally determine what percentage of their total
digital capacity will be devoted to their own video services that
don't impact usage/bandwidth caps, vs. general purpose Internet access
(and the competing video services that depend on this), in terms of
Internet speed, latency, usage caps, and so on.

So becoming too diverted by the details of the technology in this case
is an easy way to lose track of the ball -- and you'll find that often
those parties who most oppose Network Neutrality concepts will attempt
such diversions as a matter of course. 

That's how I see it, anyway.

NNSquad Moderator