I bought the Router TP-Link TD-W8968 v3, since it support both ADSL and 3G . If the ADSL Fails, 3G will be connected automatically (Fallback) where this functionality is not working.
http://www.tp-link.com/en/products/details/cat-5030_TD-W8968.html
I made a complaint to TP-Link India, after...