To support analog voice applications in the TSU multiplexer, ADTRAN has several modules available that provide FXS, FXO and E&M interfaces. For flexibility, the analog voice modules come in a variety of formats. These modules provide a quick and simple upgrade path for TSU multiplexers requiring support for PBXs, KSUs, analog telephones, dial-up modem pools, fax machines and leased line modems.To support station side connectivity for analog interfaces, the FXS+ modules offer several connectivity options. The Quad FXS+ module provides four, 2-wire voice-grade interfaces serving as the source of line-current and ringing voltage to a telephone or station interface. The FXS+ may serve as the station-side of a foreign exchange FXS/FXO application. It may be paired with another FXS+ to provide a hotline or private line automatic ringdown (PLAR) function to a remote location at the far end of the T-Span. When the FXS+ is used in the tandem mode, it can be set to accept phone service directly from a toll switch using E&M signalling on the T-Span. It may also be used to provide trunk services to a PBX from a local switch. The FXS+ is intended for use in applications where the 2-wire port wiring remains on premises.