The F.port is the new protocol developed between BetaFlight and FrySky currently available for many Sbus receivers in Beta version, for example https://www.frsky-rc.com/xsr-m/
F.port receives low-lattency Sbus control signal and adds S.port bi-directional telemetry to it. This has following benefits
No need for additional UART, as the usual UART used for Sbus can be utilized and S.port does not need to be connected
Since it's bi-directional, it can be used to tune PIDs from Taranis and also bring support to FrSky telemetry without the necessity for additional hardware inverter.
The protocol specification can be found here https://github.com/betaflight/betaflight/files/1491056/F.Port.protocol.betaFlight.V2.1.2017.11.21.pdf