After pppoeconf.
pon dsl-provider – connect
poff dsl-provider – disconnect

Read a similar post to yours here… http://www.atoztoa.com/2009/01/internet-is-up-in-ubuntu.html

Connecting BSNL Broadband using ADSL Modem with USB is almost impossible in Linux. I have tried in vain. If you find a way, please inform me at webmaster@atoztoa.com.