Comcast bursting upload bandwidth?

I was just running a bandwidth test on my Comcast internet connection and noticed that the upload bandwidth seemed drastically higher than what I’m used to. (I’m used to about 30KB/s upload.) This test said I was getting 1485kbps (~185KB/s) upload speeds and 10038kbps download speeds. So I decided to run some tests.

I started by generating a 10 MB file full of random data and then used scp to copy it to one of my servers that has plenty of bandwidth to spare. I ran this test from different locations that both have Comcast high speed internet. It appears that the bursting is per TCP session, because I can start another scp immediately and see the same results.

initial speed – ~340KB/s
at around 1MB uploaded – ~260KB/s
at around 2MB uploaded – ~280KB/s
at around 5MB uploaded – ~200KB/s
at around 7MB uploaded – ~45KB/s

This graph illustrates it much better

Upload Throttle graph

Curious, I ran a similar test with downloading. Here’s a graph of my result:Download Throttling graph

While I’d still love to have more upload bandwidth, I’m excited about this improvement by Comcast. Oh and by the way, I’m going to make use of this great download bandwidth too. (I wonder at what point I’ll get a threatening phone call from them.)

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