I tried those options but it didn't work to resolve those errors.
However, I talked with the SDO and he said that he has configured my modem to work in bridge mode, now I am still getting the same error from my router while dialling. But I noticed that the router does connect with the BSNL after returning errors.. it takes around 15 to 20 minutes to connect the router back with BSNL once it gets disconnected, I don't know if this is a problem on BSNL end or my router.. maybe BSNL allows only 1 connection attempt from router/modem within 15 minutes/20 minutes. My BSNL modem takes around 5 to 10 minutes to connect with BSNL once it gets disconnected.
However, I talked with the SDO and he said that he has configured my modem to work in bridge mode, now I am still getting the same error from my router while dialling. But I noticed that the router does connect with the BSNL after returning errors.. it takes around 15 to 20 minutes to connect the router back with BSNL once it gets disconnected, I don't know if this is a problem on BSNL end or my router.. maybe BSNL allows only 1 connection attempt from router/modem within 15 minutes/20 minutes. My BSNL modem takes around 5 to 10 minutes to connect with BSNL once it gets disconnected.