Is it possible to speed up the download without uploading at once?
Is it possible to speed up the download without uploading at once?
What that is referring to has nothing to do with the OP's issue. Running a test to a site like speed test will not magically unlock their full bandwidth. That's not how traffic engineering works
@OP This appears to be an issue with windowing with speed test being merely a coincidence to match up perfectly. As you are downloading and run a speed test, your speed test consumes the bandwidth basically cutting it off, as you see the download dip into kbps. As you start the upload speed the client sees there is available bandwidth and begin to start the download at maximum MSS size and as it begins seeing packet loss the windowing keeps getting halfed until it reaches as you see 2.5MBps. This is the best I can tell that is going on with little info.
If you just upload something instead of running a speed test and it shoots up, yeah no clue whats going on, this is odd behavior to begin with So when you send a TCP single packet a single response is needed before it will send the next packet. As you can imagine this takes time. So after a successful packet, it will send two packets before requesting a response. If it doesn't get a response or response says its missing data, it will dial back down. Everytime it does this your speeds will be cut causing less data. This is why you will see speeds ramp up like in steam or downloading a movie. However, there are some programs that I've seen do it in reverse by starting big then ramping down, kind of like what is happening with you. With all that said, speedtest.net is TCP, it should be acting similarly if it is the case. This can be cause by a few things like line quality of you are using copper or coax, or just congestion. This is just a guess without in-depth testing.