A variation of the EPON or GPON network is to add a downstream analog RF signal to the PON signals on the fiber. This is shown in Figure and has the advantages of EPON or GPON with the additional advantage of having an RF pipe to carry other signals that can be RF modulated. The xPON network carries packetized digital data, while the RF network can carry any signal, digital or analog, as long as it is RF modulated.
As telcos turn to triple-play services (video, voice and high-speed internet access) to reduce churn and increase revenue, they need to find a way of delivering TV and video to the end-user as cost-effectively as possible. In a point-to-multipoint PON architecture, one wavelength frequency is assigned for downstream data and telephony (1490 nm) and another is assigned for upstream data (1310 nm). With the RF overlay approach, through the use of wave-division multiplexing (WDM), a third downstream frequency is assigned – 1550 nm – which is dedicated to video broadcast. RF overlay is capable of delivering all types of video service: analogue broadcast, digital broadcast and HDTV, and video-on-demand.