2N Omega series - Configuration Tool manual v1.9 - Manual (Page 66)

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Here you can select where the DISA is entered in the ringing table, so that after an
incoming ringing on an external line it takes into account FAX or Modem tone in the
DTMF selection and connects to the declared internal line in accordance.
Ringing from external lines can elicit a maximum of 500 events.