D-Link DSL-3900 User Manual page 39

Section 4 - Configuration
Authentication
Select the authentication protocol your ISP uses. The options are
Protocol: Auto, PAP, or CHAP.
Connect mode Set the connection to be Always-on, Connect-On-Demand, or
select: Manual.
If you selected Connect-On-Demand, the following option is available:
Maximum Idle
Enter the amount of time the router will maintain the Internet
Time: connection before disconnecting if there is no activity.
Click Save when you are done.
D-Link DSL-3900 User Manual 35