I am posting this purely for the benefit of others ... and I would hope also that TPG Support will make a note of this and put this into the TPG Support Knowledgebase!
I just upgraded yesterday from NBN12 to NBN50 and was keen to check out the improved performance, so imagine my disappointment when I found I was getting just 10Mbps Download still. Odd thing though, was that the Upload was nearly 20Mbps. What? Clearly NBN50 was in play, but not for downloads.
Did a HUGE amount of testing, spoke with TPG Support, we eventually discovered that other computers on my home network were happily downloading at 45Mbps. Why not MY laptop? I checked the cabling path, switches, router, modem, nope, no joy. Made no difference whether using ethernet cable or WiFi.
Then I tried using the iiNET Speed Test (https://www.iinet.net.au/internet-products/broadband/speed-test/) and got 45Mbps. But with SpeedTest.NET (www.speedtest.net) just 10Mbps. What the ... ???
Alright, I know that NBN50 is working ... hmmmm ... lots of Googling and newsgroup reading ... resetting the TCP/IP Winsock stack. fiddling with Receive Window AutoTuning ... nope ... nada ... no joy ... and then I finally found the cause, thanks to some other Dell users who'd had the same issue.
Uninstall a bit of Dell-supplied software called SmartByte from my laptop. Immediately I am getting 45Mbps. Thanks Dell, thanks SmartByte, thanks a LOT, you just cost me half my Saturday day off!
