Finally the problem is solved. The TP-LINK support personnel sent me a firmware file. Upon downloading the file, I noticed that it is nothing but the initial version firmware for the MR3020 router....

I am having same issue with TL-MR3020 and BSNL EVDO AC8700M USB modem. From the router log, the response to a modem command is termed as 'invalid'. I have already sent the log to TP-link support for...