By now, it's nearly a foregone conclusion that cable providers will take advantage of a somewhat
eponymous technology — MoCA, for Multimedia
Over Coax Alliance — to handle the business of
moving the bits of video, voice and data over the
coaxial cables that already interconnect our various
cable gadgets.
Last month, a second version of the MoCA
spec emerged, which seemed a good enough
reason to take a closer look at what’s happening in
this interconnectable world of Ethernet, Wi-Fi and
its 802.11 flavors, HomePlug and HPNA.
Know going in that there’s little truth in networking,
at least as it relates to the advertising
speeds emblazoned upon the boxes in the homenetworking
aisle. If it sounds too good to be true
(500 Megabits per second!), it usually is.
Here’s why. In any communications network,
there’s such a thing as MAC and PHY. “MAC”
stands for Media Access Control. “PHY” stands
for “physical.” In raw terms, “PHY” is the gross and
“MAC” the net.
In tech terms, the “physical layer,” or “PHY,”
is where bits are modulated and coded. The
media-access control, or “MAC,” is where the stuff
happens for multiple devices on a network to
communicate — how they get access, how they
listen, how they request a slice of the PHY, for
transmitting.
Those activities of the MAC create overhead, in
the form of extra bits, moving through the network
— in other words, taking up room. Service providers,
for that reason, are much more interested in the
MAC rate than the PHY rate.
Which takes us back to MoCA 2.0, likely to be
the wired home-networking method of choice by
multichannel video operators (cable, satellite and
telco). Here’s what’s new: a throughput pop from
175 Mbps to 400 Mbps and, in “enhanced mode,”
800 Mbps. That’s the MAC rate. (PHY rates are 700
Mbps and 1.4 Gbps.)
Also interesting, from a “green” perspective: The
2.0 version of MoCA includes sleep and standby
modes for networked devices. This is good, because
set-tops, modems and their ilk do draw
power, and don’t currently have either mode.
Remember, “specifications” are blueprints. From
there, specs like MoCA 2.0 go to chip manufacturers,
then to device manufacturers, to build. Translation:
Add about 18 months, realistically, until you’ll see
MoCA 2.0-based gear in homes.
But it’s coming, and that’s good, because it’ll be
needed for homes simultaneously flinging five or
so HD streams to connected screens.
