The FOI-4066 and FOI-4606 both provide complete electrical isolation for 2-wire U-Interface ISDN communications. The FOI-4606 is also optically compatible with the FOI-4605, which allow users to create a link between the U-Interface and the S/T-Interface without requiring a separate interface converter, such as an NT-1.

The units can be used in areas of high electrical noise or in and out of RF shielded enclosures. The fiber optic cable is not susceptible to interference caused by impulse noise, crosstalk, or EMI. Privacy of communications is also enhanced because the fiber optic cable does not radiate any emissions. FiberPlex recommends “R” units for high security applications because the units have added filtering and shielding for RFI suppression.

A typical link consists of an FOI-4606 at the central office line terminal (LT) equipment and an FOI-4066 at the customer premises network terminal (NT) equipment with a duplex fiber optic cable between them.