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EPON-Over-Coax Starts Its Standards Journey

Jeff Baumgartner
LR Cable News Analysis
Jeff Baumgartner

If a new Institute of Electrical and Electronics Engineers Inc. (IEEE) project bears fruit, cable operators might be able to delay costly fiber-to-the-home (FTTH) deployments, or even avoid them altogether.

The proposed physical-layer standard is called EPON-over-Coax (EPoC), and its goal is to provide symmetrical 10Gbit/s speeds over hybrid fiber/coax (HFC) networks. It's just getting started; the first EPoC Study Group meeting will get together on Jan. 24 in sunny Newport Beach, Calif.

Here's the slide deck (PDF) that was presented during an IEEE 802.3 call-for-interest meeting last November. The IEEE voted at that meeting to form the study group, a move that simply "gives us the right to study the problem," says Study Group Chairman Howard Frazier, who also serves as senior technical director at Broadcom Corp. (Nasdaq: BRCM), a chipmaker that has been championing EPoC. (See Broadcom Crafting PON-Speed HFC.)

EPoC will need to be compatible with or work around existing cable services, which tend to vary from operator to operator and from HFC plant to HFC plant.

"There's no way operators will do a forklift upgrade. We'll have to adapt to what they're deploying five years from now," Frazier says. That means EPoC will have to coexist with QAM-based video systems, Docsis 3.0 platforms, cell backhaul deployments and the next-gen Converged Cable Access Platform (CCAP), which some view as a possible bridge to EPoC. (See Comcast Gets Ready for CCAP and Cable Rethinks 'Modular' CCAP .)

Here's an example of how EPoC spectrum might live alongside cable's other services:

QAM's big goodbye?
EPoC could begin to steer cable away from its traditional QAM modulation schemes, and this part of the discussion is expected to be among the most hotly debated as engineers mull ways to modulate Ethernet on coax efficiently.

One idea that will get much attention is orthogonal frequency-division multiplexing (OFDM), a scheme popular in the wireless world that could help cable pump out more bits per hertz than they do today with QAM, says Shane Eleniak, vice president of advanced broadband solutions at CommScope Inc.

CommScope has a chip team (that came on board via the company's purchase of edge QAM maker LiquidxStream Systems Inc.) that's been eyeing the development of a mixed-mode QAM/OFDM Application-Specific Integrated Circuit (ASIC) or a more flexible Field Programmable Gate Array (FPGA) implementation, he notes. (See Why CommScope Bought LiquidxStream.)

Frazier acknowledges that OFDM is one scheme that the working group will likely consider, but he warns that nothing's been decided. "We're going to have a very interesting discussion," he says. "We'll have to duke it out and see what works best."

But the cable industry has definitely fallen in love with EPON. Following heavy adoption of EPON by service providers in Asia, domestic cable has grown partial to the technology in recent years, increasingly relying on it to deliver business services. Taking things a step further, CableLabs has also created a spec that grafts Docsis-style provisioning to EPON services. (See Docsis Gets Its EPON On.)

EPoC timetables
Based on the usual IEEE timetable, an EPoC standard would take about three years to complete. Frazier expects some pre-standard products to start coming out in late 2013 or early 2014. "There will be trials ... but I'm thinking that the deployment horizon will start two to three years out."

He sees initial adoption of EPoC happening in North America and also in China, where it's estimated more than 190 million users are connected to coax today, with 300 million expected to be passed by HFC by 2019, according to China's State Administration of Radio, Film, and Television (SARFT).

Here's who's supporting EPoC so far:

Table 1: EPoC Dudes

Alcatel-Lucent Aurora Networks Inc. Bright House Networks
Broadcom Corp. Cogeco Cable Inc. CableLabs Inc.
Comcast Corp. Cox Communications Inc. Dell Inc.
FiberHome Telecommunication Technologies Co. Ltd. Harmonic Inc. HP
High Speed Design Huawei Technologies Co. Ltd NeoPhotonics Corp.
PMC-Sierra Inc. Qualcomm Inc. Sumitomo Electric Industries
Technical Working Committee of China Radio & TV Association Time Warner Cable Inc. Wuhan Yangtze Optical Technologies Co. Ltd.
ZTE Corp.
Source: IEEE

— Jeff Baumgartner, Site Editor, Light Reading Cable

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User Rank: Light Sabre
12/5/2012 | 5:46:03 PM
re: EPON-Over-Coax Starts Its Standards Journey

... not that it matters.

Why would an MSO go to a different PMD/MAC on legacy HFC plant?  Expecially since DOCSIS is reasonably well optimized for the HFC environment, and EPON was designed for PON.  So, for example, DOCSIS can use contention/reservation for upstream grants because receiver overload is not damaging.  GPON has to use polling/reservation, which is fine because of the relatively small split ratios in the PON, but would (I suspect) tend to be pretty inefficient with a 125:1 split or bigger.

It looks like this scheme is going to require replacing every node, amplifier, and passive in the network to get above 1GHz.  Not that this is unprecedented, but experience shows that this is a non-trivial and expensive enterprise.   We've seen several schemes like this fail to get traction because of the cost of the upgrade.    And it looks like the upstream/downstream bandwidth asymetry gets worse rather than better.  So if you're going to forklift anyway, why not move the high/low split?

DOCSIS 2.0 and above have a more specrtrally efficient upstream modulation scheme, S/CDMA.  How it might compare to any OFDM scheme that 802.3 might come up with is not clear.   While it's likely that there are more spectrally efficient downstream schemes than bonding together 6MHz channels of 64-QAM, I'm not quite seeing downstream efficiency as the long pole in the tent.

It's also not unprecedented for the industry to get distracted by shiny new objects.  Or start up new standards activities with no serious plan to deploy them.

Perhaps somebody with better insight can explain?

Carol Wilson
Carol Wilson,
User Rank: Blogger
12/5/2012 | 5:45:58 PM
re: EPON-Over-Coax Starts Its Standards Journey

I'm not a cable guy and I can't address the issues raised in terms of the modulation schemes or the cost of the upgrades, but in the telecom world, the biggest chunk of change in deploying PON was always  the cost of putting in fiber optic cable to every home. Wouldn't those economics play out here as well?

User Rank: Light Beer
12/5/2012 | 5:45:56 PM
re: EPON-Over-Coax Starts Its Standards Journey

In Chestnut Hill,Pennsylvania, there are literally no LEs (line extenders).It is all optical nodes in that Comcast service area because that's why Ralph Roberts and other big wigs in the company live,and use to live.Anyway, my point is that cablecos can do away with LEs all together and allow a single node  to serve about 250 subs.The taps at each location can be converted to optical transceivers and be powered by the same existing hardline coax from the node.In other words, the electronics inside the housing of the node would contain a fiber port and a power output to power the optical transceiver taps.The taps would convert light to RF and vice versa because they would still use the existing coax drop to the home.However,for plant extension, a reserve optical port would be provided.

The cost involved may not be as labor intensive as Verizon Fios because the fiber is already there at the node.The only problem is getting this done where existing plant is underground,and permission for digging up properties and roadways may result in several stumbling blocks as Verizon has found out the hard way.

Despite the affore mentioned diffulties, the approach may be beneficial in the long given the there would be less power consumption from cascading amplifiers, less noise as there won't be any other noise figure (NF) than what is produced by the node.In terms of power outages, the maintenance technician would have a single amp to contend with to apply standby powering.This approach may even be better than RFoG( RF over glass.) Also with no amp cascades, the cablecos will not only able to exceed a 1GHz,but able utilize almost all of the sub-band frequencies.

What do you think?

User Rank: Light Beer
12/5/2012 | 5:45:46 PM
re: EPON-Over-Coax Starts Its Standards Journey

I think the appeal of EPoC will vary depending on the plant and the channel line up at the particular MSO/region and so will the optimal spectrum splitting. The Chestnut Hill scenario would seem ideal for an upgrade like this. The problems that the initial post raised from the interestingly named "Duh!" are real. However they apply as well to any solution that requires an increase in the upstream spectrum, whether it be more DOCSIS 3.0 channel bonding or a new MAC/PHY like EPoC.  The fewer actives between the node and the subscriber the easier it will be to make the change. The main problem with the current HFC plant spectrum allocation is that the upstream bandwidth is very small compared with the downstream and it is the lowest SNR spectrum available.  In some cases the 5MHz to 12MHz bandwidth is not really useable or only usable with low bits/Hz modulation such as QPSK. This leaves only 42MHz-12mMHz = 30MHz of bandwidth vs > 700MHz for downstream. It is changing the amplfiers, lasers, and diplexers to fix this problem that costs money.

The question of whether the EPoC spectrum must be placed above 1GHz depends on whether the additional upstream bandwidth comes by expanding the current upstream band vs placing it above 1GHz or at high frequencies and also whether bandwidth below 1GHz can be reclaimed via elimination of the analog channels or replacement of the QAM channels. Again, probably the answer differs from one MSO to another.

At first like "Duh!" I was puzzled by the proposal for yet another new modulation scheme beyond the well established DOCSIS 3.0. Do we really need another way of sending data over coax? It is true that some more bandwidth can be squeezed from the plant by using OFDM. There are proposals to use OFDM QAM constellations as large as 4096. However this requires a signal to noise 12dB higher than needed to support the current QAM-256 and only results in 50% more bandwidth (apples to apples not counting elimination of wastful D3.0 guardbands etc.)

I think that the more important consideration may be the cost of the electronics at the headend and home. PON equipment has already been reduced in cost to consumer levels due especially to price pressure from China operators. Considering an EPoC media converter would be shared by multiple homes, the already low PON electronics/optics cost/sub will be further divided.  OFDM is now low in cost since it became the universal wireless solution for WiFi and 4G. Putting the two together could result in a low cost solution compared to DOCSIS 3.0.

Of course everything depends on volume. If the EPoC solutions become splintered by using many different spectral plans or worse, multiple PHYs, and if EPoC is only embraced in the US and not world-wide then the cost reduction may not be compelling.

Time will tell.

User Rank: Light Beer
12/5/2012 | 5:45:45 PM
re: EPON-Over-Coax Starts Its Standards Journey

We seem to be on the same wavelength (or should I say frequency?), "Duh!"

User Rank: Light Sabre
12/5/2012 | 5:45:45 PM
re: EPON-Over-Coax Starts Its Standards Journey


I was thinking that the only plausible rationale might be something along the lines you're talking about:  effectively, EPON with coax drops. 

I suppose something like that might be feasible.  Trying to overlay it on existing services will be difficult and expensive.   Building a very low cost, energy efficient media converter + optical power splitter that will be a drop-in replacement for (and act as) a multi-tap will be a challenge.  I image that such a device will have somewhat more RF insertion loss than a multi-tap, which may or may not be a problem.   Plus there will be challenges with powering and ODN engineering for the distributed split.  And big construction expenses to overlash fiber on coax.

If that is the architecture they have in mind, it will be interesting to see it play out.


User Rank: Light Sabre
12/5/2012 | 5:45:45 PM
re: EPON-Over-Coax Starts Its Standards Journey

That wasn't the question.  Without a doubt,  an incumbent with existing coax plant would hope to defer investment in brownfields FTTH infrastructure for as long as possible.  And bandwidth(Hz)/reach curves for coax puts them in a favorable position for doing so, relative to incumbents with existing copper pairs.  

There are lots of good ways for MSOs to increase the downstream bandwidth (and SNR) available for DOCSIS-based services.   They are doing most of them: eliminating analog channels, plant clean-up, SDV, 1GHz upgrades, node segmentation, "fiber rich" architectures.   The long pole in the tent is the limited amount of upstream bandwidth, which is a much more difficult problem.

What I'm seeing here doesn't seem to address those problems.   In fact, I'm not clear as to what problems it does address.

I'll be interested to see Jeff's update.

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