Yeastar SO Module 1 FXS & 1 FXO Port for S20 & P550

The Yeastar SO module is a module with one FXO port and one FXS port to offer a unique PSTN failover function, enabling you to make/receive calls even when system powers down.

An FXS interface allows to connect conventional analog phones, DECT phones, fax machines, and other devices equipped with FXO interface to IP PBX. The FXO interface allows you to connect to the IP-PBX a local phone line or any other line that is connected to the FXS interface at the other end.