RFoG Overview

RF over Glass (RFoG) is a simple Hybrid Fiber/Coax (HFC) technology that replaces the coax access network with a passive optical network (PON). It is one form of what is known as DOCSIS PON or DPON. With RFoG, the HFC head end access fiber multiplexer is replaced by a WDM device that divides the upstream and downstream wavelengths and delivers them on separate fibers to other devices in the headend. Fiber splitters, instead of HFC nodes, are deployed to serve neighborhoods. A fiber NID is installed at each house.

The image below (click to enlarge) provides an architectural overview of a traditional HFC network.

The RFoG architecture in the outside plant (OSP) is identical to that of a PON, and in fact RFoG can be deployed in conjunction with a PON. The image below provides an overview of a combined GPON and RFoG implementation. RFoG’s biggest advantage is its ability to leverage legacy systems and electronics in delivering Cable TV service. Set Top Boxes (STBs) within the home remain unchanged in a shift from traditional HFC to RFoG. The RFoG ONU on the side of the house generates/receives RF coax signals identical to those used with HFC. The operational systems that tend the headend and the CPE with an HFC access network work just fine when RFoG is used instead.

With RFoG, downstream traffic is typically transmitted at 1550nm, and upstream traffic (with each STB transmitting in turn) is typically carried at 1310nm, 1590nm, or 1610nm. If 1310nm is used for the upstream, no upgrade path to GPON or most other PON technologies is possible since they use 1310nm for upstream transmission.

Several vendors provides RFoG products today. Standards work is ongoing for RFoG in the Society of Cable Telecommunications Engineers (SCTE) subcommittee IP SP 91.

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