Changing the off-hook voltage probably won't make any difference. This is a function of the resistance of the alarm gear and the loop current. Most alarm systems are relatively brief sessions and in general similar settings to fax and modems should work, but disable T.38.
- G.711 codec only, no G.729
- No echo cancellation
- No call waiting
- no VAD
- No PLC
Changing the impedance settings on the FXS port and reducing the transmit and/or receive levels may help. This is often a matter of experimentation and trial-and-error.
Also keep in mind the practical implications on using anything requiring local power for an alarm or safety application. You want the phone in the elevator to work if the power goes off. If the UPS powering the Adtran catches fire, you want the fire alarm to work, etc. There are certain cases where a POTS copper loop makes sense and alarm lines often fall into that category.
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Answer was correct & Perfect. Thank YOU