Thanks Vivian & Johnson, now the problems is solved, actually I had to update firmware of my modem, now it is working properly.

johnson wrote Can you confirm your TD-W8901N is working well first? Which mean that you can surf the internet through the TD-W8901N. Then I will tell you how to extend an existing wireless network's...

Model : TL-WA850RE(eu) Hardware Version : V1.26 Firmware Version : ISP : I just bought wifi extender TL-WA850RE(eu) ver 1.26 from Amazon, but my modem TD-W8901N does not have WPS button and after...