The FOI-3901 and FOI-3902 both provide complete electrical isolation for Nortel’s Meridian M2000 and M3000 series digital telephones. The FOI-3901 connects to the digital line card and automatically senses and corrects any improper polarity reversals on the RJ-11. The bidirectional signaling between the digital line card and telephone is then carried across a duplex fiber optic cable. The FOI-3902 reproduces the digital signaling at the isolated end of the fiber optic link and provides power sufficient to operate M2000 and M3000 series digital telephones.

The FOI-3902 is compatible with Nortel’s A0367335 plug-in transformer, which provides power to support the additional features on the M2016S digital telephone. A closet power supply can also be used to provide auxiliary power but the power must be inserted between the FOI-3902 and the digital telephone.

In addition, fiber optic cable offers much longer transmission distance than traditional telephone line cord wiring. Nortel’s Meridian digital telephones are limited to a maximum distance of 1750 feet (458m) from the PBX to the telephone on 24 gauge wire, but multimode and singlemode optics on the units can extend the distance to 2km. A typical link consists of an FOI-3901 at the PBX and an FOI-3902 at the telephone with a duplex fiber optic cable between them.