the chronic question of bandwidth: How many slots on the digital
shelf can go to more HD and VOD? How many for any new 3D
and Internet-protocol TV offerings?

The second prong is the matter of sheer
physical space. If you’re the keeper of headends
and hubs — heating, cooling, power, rack arrangements,
wiring — it’s not a good day when
the headend starts looking like the five-pound
bag, with another 10 pounds of new stuff on
the way.

At issue, in large part, are those impressively nerdy mainstays
of digital cable: the QAMs. Quadrature amplitude modulators are
necessary to imprint digital signals onto the physical plant, for
transmission to subscribing homes.

Pretty much everything needs a QAM in cable, including the
new stuff. But up until now, most service categories attracted their
own vendors, each with their own QAMs. There are QAM suppliers
for video and QAM suppliers for voice and data.

Right now, the densest packing of video QAMs is eight per
port. For broadband data, four. Switched digital video? Up to 16.
IPTV will need a few to start, then more as the service develops.

Right now, they all exist in isolation. Different racks, different
batches of gear.

That’s why the industry’s headend caretakers — led by Comcast
— posed this question: Why not make the QAM spigots
denser, and more capable of sending information across service

If you’ve gotten this far, you’re probably hip to a relatively
new, Comcast-specific term: “CMAP,” which
stands for Converged Multiservice Access Platform.
It grew out of another Comcast acronym:
“NGAA,” which stands for “Next Generation Access

If you dabble in the cable-modem termination
system landscape, this is probably sounding
a lot like the “modular CMTS” conversations
that dominated the broadband cable scene a few years ago.

This is different, in that it’s a blueprint for gear.

Here’s what CMAP isn’t: It’s not a new version of DOCSIS,
nor is it an active CableLabs project. That’s because it’s a product
definition, not an interface specification. In other words, it
doesn’t mess with how data talks when it moves from one port
to another. Instead, it suggests a way to mix and match QAMs for
video, voice and data services, in a denser way. 160 of them, per
port, with room to grow.

This is at the write-the-specs stage now. They turn into
CMAPs as soon as next year, with launches expected the year
after. More on this as it develops.