Translation Please

DPoE, EPoC: What's It All About?

3/05/2012 9:35 AM

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 maneuver.

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- Gigabit-per-second services.

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 end points.”

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. That’s EPoC.

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-but-goodie 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 speeds.
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