D-Link DIR-660 User Manual page 35

Section  - Configuration
If you have an unusual network connection in which you are actually connected via xDSL but for which you configure either
"Static" or "DHCP" in the Internet settings, setting this option to xDSL or Other Frame Relay Network ensures that the router
will recognize that it needs to shape traffic slightly differently in order to give the best performance. Choosing xDSL or Other
Frame Relay Network causes the measured uplink speed to be reported slightly lower than before on such connections, but
gives much better results.
Detected xDSL: When Connection Type is set to automatic, the automatically detected connection type is displayed here.
D-Link DIR-660 User Manual