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The Foreign Exchange Office (FXO) and Foreign Exchange Subscriber (FXS) modules are used in the Total Access solutions to provide analog voice extension. The two units may be used in a back-to-back configuration. Here, the FXO interfaces to the central office switch, and the FXS interfaces to the customer's telephone. Or, the more common configuration uses an FXS only, with the T1 interfacing directly to the CO switch (TR-08 mode).
Four analog voice ports on the FXO/FXS access modules provide four individual connections to the switch or customer telephones. The units support standard loop start, ground start, and TR-08 signaling options. In addition to these signaling states, the FXS supports E&M to wink start, E&M to ground start, and several immediate start signaling states. Direct Inward Dial (DID) applications are supported with the Dial Pulse Terminate (DPT) and Dial Pulse Originate (DPO) functionality found on the FXO and FXS, respectively. A unique feature of the FXS access module is the automatic gain provisioning option. This feature automatically adjusts the gain for short and long loops, therefore expediting installation time and decreasing provisioning errors. The auto gain feature may be overridden as a software function via the craft interface.
For further flexibility, the FXS may be deployed on long loops, up to 1200 ohm impedance. V.90 modems are supported on both units ensuring customer satisfaction. Both access modules are hot swappable and accessible at all times. An individual access module may be replaced without disrupting other units. The Quad (4-circuit-per-card) design ensures a maximum of only four analog circuits are affected when replacing an access module.