Canon MX520 series Fax Manual page 68

Pick up the handset, and talk on the telephone.
Note
To use this feature, you need to subscribe to a
compatible service provided by your telephone company.
For DRPD
You need to select the appropriate ring pattern on the
machine.
Setting the DRPD Ring Pattern (US and Canada only)
For Network switch
The name of this service varies depending on the
country or region of purchase. This setting may not be
also available depending on the country or region of
purchase.