My setup of having TP Link wireless router with PTCL Broadband modem was working fine. But I was getting bad internet on my mobile phones and PCs. If I bypass the wireless router and connect DSL modem directly, it start working fine.
So it seems issue is with wireless router. And I used to get error in my browser that DNS named not resolved.
Error 105 (net::ERR_NAME_NOT_RESOLVED): Unable to resolve the server’s DNS address.
The admin panel of my PTCL Broadband is on 192.168.1.1 and for TP-Link I set to 192.168.2.8. I replaced the primary and secondary PTCL DNS with Google Public DNS. And it works (Primary: 188.8.131.52 and Secondary 184.108.40.206).
Google Public DNS is a free, global Domain Name System resolution service, that we can use as an alternative to PTCL DNS. I am observing quality of Internet speed now.
You can also use OpenDNS addresses other than Google. Primary: 220.127.116.11 Secondary: 18.104.22.168. I will give try to OpenDNS too.