Yeastar SO Module (1 FXS + 1 FXO Port)

The Yeastar SO Module is an innovative hybrid telephony expansion module that combines 1 FXS analog extension port and 1 FXO analog PSTN trunk port on a single board. Designed with mission-critical continuity in mind, the SO module features a hardware PSTN Lifeline feature. In standard operation, the FXS port drives an internal telephone extension while the FXO port connects an external PSTN central office line. If power to the PBX fails completely, an onboard mechanical relay automatically loops the FXS phone directly into the FXO line, enabling emergency outgoing calls even in total blackout conditions.