My T-Mobile Home Internet service (unlimited plan) has been working great for the past 18 months. Download speeds consistently in the 175-450 mbps range (usually 250-350) when running speedtest.net using Ethernet connection to my gateway.
2 weeks ago my download speed suddenly dropped to 15-30 mbps consistently (speedtest.net) - a 10x reduction. Strangely enough my upload speed remained good at 25-50 mbps consistently. There’s a long story about many calls into Home Internet and Customer Care support numbers, bottom line is that everyone kept telling me it’s a cellular problem (connection between tower and my gateway) probably caused by shifting antenna positions on the tower due to the maintenance. This never made any sense because why would my upload speed not be affected if the cellular connection was bad? Making even less sense: All the metrics on my gateway look very good: 4 bars displayed on front panel, 5G RSRQ of -11, 5G RSRP of -72, 5G SINR of 40, 5G band N41.
Today I discovered the real problem. Using speedtest.net one can select different test servers. It turns out speedtest.net has been automatically selecting servers that produce the very slow download speed results. Manually selecting other servers, I found some servers always give good download speed results, other servers always give bad download speed results. This is entirely repeatable and consistent.
So is it a problem with those specific test servers speedtest.net uses? It turns out no. My next test was to enable a VPN connection using NordVPN to one of their VPN servers in a different USA city. I went back and ran speedtest.net to all of the slow servers, all of them were back up to good/fast download speeds when tested through the VPN. In fact all of the available servers in speedtest.net now reported good/fast download speeds (when tested through the VPN).
Conclusion: It really seems like T-Mobile Home Internet is artificially throttling connection speeds to certain servers. There is obviously nothing wrong with my Gateway nor my cellular connection to the tower because through the VPN I can always get good download speeds from all of the test servers. 100% repeatable and consistent results. Sadly none of their technical group personnel seem to know this - they always check their coverage map and say I’m in a bad spot and the problem must be a bad cellular connection (despite the good metrics reported by my gateway).
T-Mobile advertises that their unlimited Home Internet service does not throttle other than for tower congestion, which is entirely reasonable. However my testing shows that they are throttling for other reasons. I’ve communicated this additional information to the support ticket I’ve had open for the past couple of weeks, will be interesting to see if they will do anything with it.