Yeastar O2 module is a module with 2 FXO ports to terminate two analog PSTN (POTS) lines. It is compatible with Yeastar S-Series VoIP PBX and P-Series PBX System.
Yeastar B2 is an optional module designed for installation in most Yeastar PBXs. The B2 module provides support for two BRI ports, allowing the Yeastar PBX to be connected to an ISDN telephone network.