Apparent Internet upload throttling=

All my equipment is working and there are no other active users of my network currently. My speed tests are showing 30 MB/s uploads, and my downloads are very fast. I can download files in my web browser quickly, and upload too.

However, I have a copy of a big file (10 GB) from my Mac to work, and I'm using "rsync" (tcp/22 over ssh) to copy the file. It's starts out great, above 50 MB/s, but quickly drops to under 1 MB/s, with speeds around 800kB/s being typical. Other protocols are fast. This is not a problem on the work end of things.

I'm pretty sure that port 22 is being throttled, but I'm not sure if my home Xfinity router is doing this, or if it is some other upstream Xfinity router.

Is there an report page or interface or someone I can contact to get more information about what is going on?