I see a lot users having trouble with getting in to the modem/gateway configuration page a.k.a http://192.168.1.1.
Follow the steps below to get to the configuration page.
1. Disconnect the phone line from the modem.
2. Configure your TCP/IP settings in Windows by going into Network Connections and right-click on LAN:
4. Enter the values as shown and click OK:
You should now be able to access your BSNL modem/gateway. Remember to change these settings back to “Obtain IP address automatically” and “Obtain DNS server address automatically” once you have configured your gateway’s DHCP server. Read this post on how to do configure your DHCP server.