DOCSIS, THE CABLE-MODEM SPECIFICATION,
is a teenager this month (turning 13
on March 20), which made us wonder
about the road map for the industry’s
most successful interoperability
Namely: We’re up to version 3.0.
Is there a DOCSIS 4.0?
Answer: Maybe not by that name,
but one just-as-sexy (ahem) acronym
is making steady inroads. It goes by
“EPoC” (pronounced “ee-pock”), and stands for
Ethernet PON over Coax. So, another nested
acronym; PON stands for “passive optical network.”
That nested PON is what links EPoC as a cousin
to “DPoE” (DOCSIS Provisioning over EPON,” where
the “E” in “EPON” is Ethernet). We’ll get to that.
Generally speaking, EPON is a big deal in the
business-services marketplace as a way to install
low-cost, high-volume gear for symmetrical, multi-
EPoC, as a variation, supplants the fiber necessity
of PON with coax. It says, “I don’t need fiber to
the anything (basement, building, house). Instead,
I’ll convert that optical signal into a bidirectional
electrical signal, then send it over coax to multiple
Think of it in an apartment sense. Fiber to the
building, coax in the walls. Something was needed
to adjoin what came in over glass, to coax. In a
cable sense, that’s DPoE — a way to spoof the
DOCSIS back-office components into thinking that
an optical transmitter (a PON term) is a CMTS, and
an optical receiver is a cable modem.
Then take a big step back. Instead of fiber to the
building, then to apartments; fiber to a node serving
500 homes. Put that optical-to-electrical converter
there, right where light is being converted to RF already.
Sounds great, you say. Where does it go spectrally?
It’s not exactly like today’s cable operators
are brimming over with available bandwidth.
Good point, and welcome back to the oldie-butgoodie
about widening the upstream signal path.
All such discussions trigger decisions about the
fielded base of amplifiers and “passives” — gear
that passes signal without needing electricity. Like
like taps and splitters. As little futzing as possible is
always a design goal there.
One school of EPOC thought moves the upper
boundary of the upstream band to 200 MHz from
42 MHz. Including spectral padding to prevent
cross-modulation, that lands the downstream signal
path at 250 MHz to 1 GHz.
Then, attention must be paid to what’s already
sitting in the spectral areas within the change zone
— 42-200 MHz, in this scenario. Lots of digital
set-tops are wired to receive command-and-control
signals (guide data, etc.) at a specific location within
that region, for instance (122 MHz).
Watch for this one, and DPoE, to get louder this
year, in your broadband engineering circles. DOCSIS
4, EPoC, whatever it’s called, something like it is
coming, and it’ll move the needle again for broadband
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