ADTRAN SMART/RG SR506n Quick Start Manual page 6

Enter the username and password and click OK. The default credentials
are admin and admin.
Note: Your service provider may use other settings. Please contact your
provider for login information.
The Device Info summary page appears.
Configuring the WAN Manually
If the automatic connection process is unsuccessful, refer to the Advanced
Setup > Layer 2 Interface and WAN Services sections of the Gateway User
Manual to manually establish a connection.