Change advanced PPP options on Mac
If you’re using a dial-up modem, you can control:
When your modem connects and disconnects from the Internet
How long your modem stays connected when it’s inactive
How many times the modem redials your ISP if the line is busy
On your Mac, choose Apple menu > System Preferences, then click Network.
Select your modem in the list at the left.
If your modem isn’t in the list, click the Add button at the bottom of the list, click the Interface pop-up menu, then choose Modem (internal or external). Give the service a name, then click Create. Enter the information you received from your ISP, such as the telephone number the modem dials, the account name, and the password.
Click Advanced, then click PPP.
Select the settings you want to use with your modem.