Cable Tech

Who Makes What: RFoG Systems

This month we're taking a rest from trying to nail down immense technologies involving scores of vendors across a range of subsectors, such as in Who Makes What: 40- & 100-Gbit/s Systems and Who Makes What: LTE Equipment.

Instead, this Who Makes What takes a narrow look at some aspects of a highly specific technology that nevertheless looks set to push another chunk of access networks into the fiber world. This is Radio Frequency Over Glass (RFoG), and it properly refers to the looming Society of Cable Telecommunications Engineers (SCTE) SP910 standard for replacing coax in today's hybrid fiber/coax (HFC) cable networks with fiber all the way to the customer's premises.

The RF part comes about because the whole point of the exercise is to preserve the 1-GHz-bandwidth analog RF signals and channel structures that support current cable services – TV, switched video, VoD, VoIP, Docsis data, and all the rest. So it's the minimum possible change to take cable into the fiber world – the big hassle and costs of replacing CPE and operator backoffice systems, for example, are avoided. In a way, it is the converse of telco DSL. That kept the copper pairs, but changed the signals; RFoG keeps the signals, but changes the coax.

It's an idea whose profile has been on the rise for some time, a trend underlined by the recent spate of approvals of vendors' RFoG equipment by the U.S. Department of Agriculture's Rural Utilities Service (RUS) for use on projects funded by the Rural Telecom Infrastructure and by the Broadband Loan and Loan Guarantee Program. Alloptic Inc. , Aurora Networks Inc. , CommScope Inc. , and Hitachi Communication Technologies America Inc. (Hitachi-CTA) have been some of the lucky recipients of such status this year. Such approvals also allow the equipment to be deployed under the Broadband Initiatives Program (BIP), which the Department is managing within the American Recovery and Reinvestment Act (ARRA) to construct broadband infrastructure in unserved and underserved rural areas.

Why RFoG?
The irruption of U.S. rural politics into the story makes the point that RFoG looks a prime candidate for a win/win quick fix to the vexing problem of kick-starting the building of next-generation fiber networks (which just about every policymaker wants now) in areas where the economics are shaky or the operator has limited resources. And, since many of the smaller U.S. cable operators are also divisions of their local telcos, there is a nice synergy, as the resulting all-optical access network is what the telco business wants, anyway.

Further, the general logic of an RFoG-based incremental upgrade to all-fiber cable seems to be acquiring wider appeal, and many cable operators (telco-owned or not) are now interested in the possibilities of RFoG.

"I think that MSOs are very enthusiastic – more enthusiastic today than they were even six months ago," says Tom Williams, VP marketing, of cable-equipment vendor Arris Group Inc. (Nasdaq: ARRS). "This comes from their realizing what is possible with an RFoG deployment in the additional applications that are made available to them, which equates directly to additional revenue. In addition, the capex costs continue to decrease, allowing a lower cost of entry for the MSO. In our own solution, for example, we have continued to innovate our headend optics to drive cost out, giving an almost a 50 percent cost differential from our earlier solution. And in addition to the capex savings there are also opex savings through the reduction in maintenance and powering of an active infrastructure."

However, it is still early days for RFoG, and it is still a small business for those vendors with pre-standard versions of the technology. Furthermore, interest is mainly about small systems, particularly small-scale, incremental new build, and no one appears to be looking at retrofitting existing large HFC deployments. This is hardly surprising as much of the coax in U.S. HFC networks is fairly new, and it could easily be another 10 to 15 years before a big switchout might start to be needed from the point of view of physical deterioration and investment amortization.

So, essentially, RFoG right now is seen both as a way of future-proofing new build and also of making more bandwidth available to added customers (business and residential) via new PON-type services.

Now that telco fiber is becoming mainstream, cable operators have little choice but to respond, and this helps to make the RFoG option attractive. Many cable operators have already been deploying PON overlays for business data services for several years in the U.S., while continuing to serve residential customers with standard HFC. An evolution that would cap the expansion of HFC while increasing fiber would make a lot of sense.

"Operators know that competition is out there, and they are searching for the best ways to answer it," says Jim Farmer, chief technology architect of optical telecom vendor Enablence Technologies Inc. (Toronto: ENA). "Options include, of course, RFoG, Docsis 3.0 over RFoG and/or HFC, going directly to EPON or GPON, waiting for 10-Gbit/s PON, further subdividing nodes, rebuilding systems to 1-GHz, analog reclamation, and switched digital video. All these options one way or another expand a cable operator's ability to compete with others who are putting in FTTH today, but all come with their unique prices and opportunities in terms of dollars, new procedures, training needs, subscriber disruptions, service tradeoffs and operational expenses."

For its supporters, a further, very strong characteristic of RFoG is that it is (or will be) a standard, in a way that other approaches are not (yet, if ever for some of them).

"We are attempting to make the 910 standard the universal standard for RF-only-based PON systems," says Farmer, who is involved in the development of the RFoG standard. "This is to ensure that an operator can remove vendor A's R-ONU from a home and replace it with vendor B's R-ONU and have everything work exactly as it did with vendor A. Beyond that, the detailed system design is up to the operator, just as in HFC design. We are defining the system such that it can be overlaid or replaced by EPON or GPON, without the need to change any of the fiber."

Other approaches (see next page), such as those based on placing the RF return path into the upsteam EPON or GPON baseband data, are essentially still proprietary.

And, policy and standards apart, RFoG resonates with some other perennial and also new concerns for cable operators.

"The technology is very environmentally friendly," says John Dalquist, VP marketing, Aurora Networks. "It is very green and very low power consumption for the cable operator. So some cable operators focused on reducing their power consumption and carbon footprint see our Fiber Deep solution (which is one of our key coaxial-to-the-home solutions) and RFoG PON as being a tremendous way also to reduce their costs and carbon footprint."

RFoG thus sounds very promising, but it is still early days for a fairly specialist technology. So what's on the market, and what has the small group of vendors involved been doing recently? And where do they think it may be going?

Here's a hyperlinked contents list:

— Tim Hills is a freelance telecommunications writer and journalist. He's a regular author of Light Reading reports.

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