At a Communications Technology-hosted webcast last week, panelists discussed how RF over Glass (RFoG) might provide a migration from HFC to fiber for cable operators.

But the one operator on the panel predicted a moderate-paced transition to fiber.

"We expect HFC to scale as a viable technology for many years to come," said Bob Harris, VP of network planning and architecture for Time Warner Cable.

Harris predicted a natural resistance to change, coupled with "last-gasp technology efforts" to promote HFC and constrain other solutions. But he noted that RFoG’s benefits include a lower opex cost due to the passive nature of the plant. Also, the fiber layout for RFoG is identical to EPON and GPON systems, which allows a level of compatibility.

"RFoG is still an asymmetrical solution so there are areas of concern there," Harris said.

Leonard Ray, a business development manager at Cisco, said HFC has been a very successful architecture because of its versatility. For an RFoG solution to replace HFC it would have to be versatile in these ways, according to Ray:

•    Support migration to DOCSIS 3.0 upstream four 64 QAM channel bonding (modem min/max +51dBmV)
•    Enable transition to multiple DOCSIS devices, such as tru2way DSG devices (10-15dB loss)
•    Mirror FSAN and IEEE PON link budgets; for future needs (28 dB @ 1310 nm & 26 dB @ 1610 nm)
•    Simple installation (plug and play)

Distance was the lead topic for Bill Dawson, VP business development and product strategy for ARRIS. The reason that distance matters for RFoG is that two leading applications—greenfield and rural builds—are usually either built beyond existing HFC networks or else spread out by definition.

Dawson said an RFoG repeater platform is a straightforward solution for obtaining reach longer than the standard 20km of PON architectures. Typical functions would include downstream optical amplification, upstream receive/combine/re-transmit and optical passives.

Meanwhile, a combination of RFoG and Gigabit EPON repeaters is likely to be a good fit for medium-sized businesses closer to existing plant, Dawson said.

Standards update

Working Group 5 of the SCTE Interface Practices Subcommittee (IPS) is preparing an RFoG architecture system description document known as "IPS SP 910," said Mark Conner, chairman of WG5.

Conner said the group gave a lot of thought in selecting the wavelengths for RFoG – 1550 forward and 1610 return – over a single fiber out toward the serving area through a splitter.

"Care was taken here to make sure that 1550 and 1610 would be clear windows that don’t overlap the other wavelengths used in these other (PON) technologies," said Conner. "There’s definitely interest among our operators to be able to in some cases use RFoG only and in some cases use RFoG with overlays from another system such as EPON."

Conner, who is a market development manager at Corning Cable Systems, said a draft of IPS SP 910 should be ready for balloting by the end of the year.

ARRIS and Cisco sponsored last Thursday’s webcast, "Fiber Optic Access: RFoG and PON Update." A recording of the event is available, but registration is required. Click here to register.

–Linda Hardesty

The Daily

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