Toshiba DKT3000 用户手册

The distinctive ring patterns available in your Centrex system are automatically repeated with your 

digital telephone, enabling you to answer appropriately for either outside, inside or callback calls.

Outside line or Centrex line(s) can be programmed for a 12-second and/or 24-second ring delay at 

stations to permit alternate answering conditions. Answer the line when your telephone is ringing.