This is how Comcast's congestion management works
said by Drizew:The pdf explains the system just fine.
Edit: I would like somebody from Comcast to chime in and maybe give us a better idea of how this all works. The analogy in the pdf was decent, but I would prefer to see some raw data. One tenth of a second is hardly a delay in delivery, but I doubt the system works as intended 100% of the time.
When you are identified as a user that is contributing to congestion on a node (and only if you fall into the "if more than 70 percent of your max bandwidth (downstream or upstream) is used for more than 15 minutes" then your packets will be marked as lower priority for the next 15 minutes. There is no throttling.
Here is a simple metaphor:
You and 10 other people have drain pipes. All 10 drain pipes feed into a single sewer line.
Everyone's pipe can drain 10 gallons per second
The sewer can drain 70 gallons per second.
If all 10 users are draining at 7 gps or less, no problems.
If all 10 users are draining at 7gps, and then you start draining at 8pgs, there is now an extra gallon per second that cannot be drained. water backs up. At first, it backs up equally across all 10 of you, so you get 7.9gps, and everyone else gets 6.9gps. After 15 minutes, your water is made to wait so everyone else's water goes first. You get 7gps, and everyone else does too. If another user drops down to 6gps, you'll get 8gps - your water soaks up EXCESS capacity, but no longer GRABS capacity from other users.
It's not a perfect analogy, but hopefully it helps clarify things.
To recap, you can use 100% of your pipe all day and night (for a few days, anyway, then you'll hit the cap - a whole different ball of wax) as long as the nodes you pass through are not saturated. If they become saturated your packets go to the 'bulk' category - you soak up all the excess capacity of the node, but if someone else needs it, your packets wait.
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