I previously blogged about a strange problem I’ve been experiencing where my internet upload speed tests fail to reach the expected gigabit speed that my ISP provides — but only in Windows 10. I have a quick update on where I ended up with this problem, and a collection of further test results that point the finger at Windows 10’s TCP stack.
I didn’t mention this in my previous post, but the Seattle server I’ve been using for all of my testing (and seeing the problem with) is run by my ISP. The main thing I figured out, and I’m embarrassed I didn’t try this earlier, is that I do get my full upstream speed in Windows 10 on some (but not all) other nearby test servers, one of which is also run by my ISP.
I’m going to start this post off by saying that I feel incredibly spoiled to even be bringing up a problem like this given that I started out decades ago on a 33.6k dialup modem and today’s cable and DSL connections still have relatively low upstream bandwidth. But it’s still a technically interesting issue that I think is worth bringing up to a larger audience. The gist of what’s going on is: I’m lucky enough to live in an area where symmetrical gigabit fiber internet is available, affordable, and maintained by an awesome ISP. The problem is that although my downstream speed is fine, I’m not seeing my full upstream bandwidth during speed tests when I’m using Windows 10. I’m “only” getting around 300 to 400 megabits instead of the expected 940-ish I should see with a wired Ethernet test.
