D-Link DSL-2520U User Manual page 24

Section 3 - Configuration
Set PVC values which are from your ISP on VPI/VCI
Set Virtual Circuit to enable mode when you want to use this PVC.
For ADSL QoS setup, modify Service Category according to your ISP's
suggestions.
Click on the Save Settings button to use this configuration.
D-Link DSL-2520U User Manual 24