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What is RFoG (Radio Frequency over Glass Fiber)?

RFoG refers to Radio Frequency over Glass Fiber. It is a specific type of optical networking, that transports the RF signals that go over copper, to a Passive Optical Network (PON). It is standard ANSI/SCTE 174 2010 (pdf) of the SCTE. RFoG figures into a Hybrid fiber-coaxial network (HFC), which is the term for a broadband network that combines optical fiber with coaxial cable, with the optical fiber as the backbone, and the coax goes to the premises as the drop.

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With RFoG, the coaxial portion of the HFC is changed to a Passive Optical Network (PON), which uses a single mono-mode fiber as the ‘last mile’ solution. This offers that advantage of higher bandwidth, with less interference compared to the coax that it replaces. By replacing the coax copper going to the residence, RFoG technology enables a fiber to the home (FTTH) solution, and is considered a ‘deep fiber’ network design.

Downstream and return path transmissions utilize the same fiber, but are separated on to different wavelengths of light. The downstream wavelength is typically 1550 nm, while the upstream is more variable using the 1590/1610 nm, or 1310 nm wavelengths.

RFoG deployments have been slow to date. While RFoG has the advantages of higher reliability, better scalability and higher bandwidth, the downsides of additional upfront equipment expenses, and the cost of deployment have hampered wider adoption of this otherwise promising technology.

With the inherent advantages, and despite the issues, there have been some carrier deployments to date. Of the cable carriers, notably, Comcast has used RFoG for a FTTH solution, in the Jacksonville, Florida market with fiber optical cables going directly to the user’s premises for true FTTH. Another carrier that uses RFoG is Verizon Fios, for the video portion of their service. Finally, Altice is building out their fiber network with plans (and promises) of FTTH, that is rumored to be using a variant of RFoG technology.

While RFoG still holds quite a bit of promise, it does compete with the easier to deploy DOCSIS 3.1, that requires less startup costs. While RFoG may be less expensive over the long term, with less interference, these advantages can be hard to justify to shareholders that want a return on investment for the next quarter, and not over years out, where the benefits of scalability and less maintenance pay their dividends.

RFoG remains a viable 'last mile' solution, for implementation of FTTH. Feel free to discuss opinions, experiences, and frustrations with RFoG as a last mile fiber solution.

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Most recommended from 14 comments



Zenit_IIfx
The system is the solution
Premium Member
join:2012-05-07
Purcellville, VA
·Comcast XFINITY

13 recommendations

Zenit_IIfx

Premium Member

Corrections

RFoG doesn’t compete with DOCSIS3.1. They coexist. DOCSIS is the main data access protocol on RFoG. The whole point of RFoG is to let Cable MSOs transition to FTTP while preserving their investment in customer premise equipment and headend equipment. Functionally, RFoG is identical to standard HFC, but with the added benenefit of a cleaner signal as you mentioned.

While RFoG is more scalable than a coax last mile solution, I think you would find that in 99% of RFoG deployments speeds are about the same as a modern HFC system. The reason being is your mini node/ONU will not have its own dedicated CMTS ports, it will be combined at the headend or hub site with the mini node signals of your neighbors. Given that most nodes tend to serve between 50-200 people depending on market and system operator you can expect a level of combining to match the norm of the specific cable system.

Why combine? The CMTS has a limited number of DS and US ports. These resources have to be carefully balanced, otherwise you end up with congestion. Too much combining of nodes can lead to congestion.