lol because my internet connection seems normal since day 1 with W8901G, i had never done the diagnostics, just did it and i got
>> Testing Ethernet LAN connection ... PASS
>> Testing ADSL Synchronization . PASS
>> Testing ATM OAM segment ping ... FAIL
>> Testing ATM OAM end to end ping ... FAIL
>> Testing ATM OAM F4 segment ping ... FAIL
>> Testing ATM OAM F4 end to end ping ... FAIL
>> Ping Primary Domain Name Server . SKIPPED
>> Ping www.yahoo.com ... SKIPPED
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anyway you can ignore the last two result, your os should be able to retrieve your isp's default dns automatically, if you can't access any domain names, then you should go to the LAN tab under Interface Setup, and configure the DNS to 202.188.0.133 and 202.188.1.5 (provided by tmnet), or you can also set them to 8.8.8.8, 8.8.4.4 (these are google's public dns), 208.67.222.222 or 208.67.220.220 (these two are provided by opendns).
Streamyx Need help setting up Streamyx on TP Link W8901G, Technical support