The MM711 provides pass through for fax signals.
The MM711 supports analog telephone sets with:
An impedance range of Rs: 215 to 300 Ohms, Rp: 750 to 1000 Ohms, Cp: 115 to 220 pF
A ringing frequency range of 20 Hz, 25 Hz, or 50 Hz
A DC current range of 20 to 60 mA
A hook flash range of 90 to 1000 ms