The Total Access 900 Series Supports the following methods of Message Waiting Indicator on Analog FXS interfaces:
FSK – FSK or Frequency Shift Keying is used to send a tone burst to an analog telephone signaling it to turn the MWI lamp on or off. This tone burst is only sent when the telephone is in and idle state and on-hook. To date FSK MWI with SIP has only been tested with the Broadsoft Feature Server for the TA 900 and TA 900e Series IADs.
Stutter Dial Tone – Stutter dial tone is an audible, broken dial tone, that the user hears when the handset is off-hook.
NEON or Voltage Message Waiting – In this method, DC voltage is applied across tip/ring to light the lamp on a phone that supports voltage message waiting. This method is typically used for hotel phones. The voltage level can be programmed to two possible values (Low 85V, High 120V).