Thanks a lot. My Zyzel nbg418n is not getting detected by my laptop wifi even after resetting ( any reason?) so i got to try with TP-Link MR3040 which has WAN port . It has AP & WISP port. Any pointers for me to get this done . ( NOTE - Reg BSNL to RAILWIRE ...Railwire FUP is better as of now )I don't know about the configuration of the ONU but I can help you with the router setup.
In the router setup, first set the mode as Router, then in the connection select PPPoE as the connection type and in that you can enter the Username and password provided my Railwire. That should get the Internet to work.
If you face you can directly talk to the LCO to help you, I got mine setup by the LCO himself but I have reset the Router several times after that.