LevelOne VOI-8001 - Manual (Page 26)

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4.2.2.5 Line configure/ Line Polarity
/VoIP Setup/Line Configure/ Line Polarity
This page defines the Polarity on the phone port of the VoIP Gateway.
If use the normal phone set to connect gateway, please select “Normal”.
If use PBX or special PSTN line (support polarity invert), then please select
“Invert”.
Please remember to press the Modify button to take it effect. For store back to flash
memory, please press Save Modification ( /System Maintenance/Save
Modification/ ).