2FXOS (Foreign Exchange Office & Foreign Exchange Station) 2FXOS is mixed interface of foreign exchange office and foreign exchange station that connect to office and station. It includes 2FXO ports and 2FXS ports, and can be combined with BRI, PRI, GSM module. FXO interfaces are used to connect your PBX to the PSTN. One FXO channel is required for each line you receive from your telco. FXS interfaces are used on the inside of your PBX, they do not connect directly to the PSTN. One FXS channel is required for each telephone that you wish to connect to your Asterisk system.

The Analog Station Interface(FXO) provides the following features:

• Ring Generation and Ringing Trip
• Loop Closure Detection
• Loop Disconnect
• Loop Reversal
• Loop Voltage and Current Monitoring
• On-hook and Off-hook Transmission
• Hook-flash Detection
• DTMF Signalling
• Programmable Audio Gain
• On-board Power Generation
• Constant Loop Current: 20mA

The loop start Analog Interface(FXS) provides the following features

• Detects ringing when on-hook
• Detects loop current when off-hook Detects when tip/ring voltage crosses a set voltage when on-hook or off-hook (called DC triggering)
• Can accommodate private branch exchange (PBX) with –48 V battery voltage
• Loop current range: 13-110mA
• Voltage detection threshold is software-selectable