US Cable Support > Comcast HSI > Is this throttling?

Is this throttling?

Comcast does not throttle, so no.
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reply to Crispyfertoo
yanking in a torrent might not be the best platform to base a speedtest on. that graph could be powerboost (though powerboost shouldn't sawtooth like that if it's a constant download.. it should start high then ramp down and be solid), or it could be comcast interfering with your torrent download.

you need to download some big files, like some linux iso's or something and see how the download goes.

reply to Crispyfertoo
»dc.testmy.net/dl-200MB&nfw=1
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»www.VAJeeps.com

man i just tried that testmy.net "speedtest" and it was totally inaccurate for my comcast connection. the graph was all over the place and only around 60% of the speeds that i normally pull day in/day out.

I'm on blast, and when i scp or rsync multi-gigabyte files from the office to my home computers, i average out at 3MB/s (24Mbps) all day long (powerboost gets me at 36Mbps or 4.5MB/s for the first 10-15 megs of the download). no dips, no fluctuations for the duration of the download, unless i'm multitasking on the net.

i guess what i'm getting at, is if i used that testmy.net as an indicator of the health of my connection, i would be going off of completely incorrect data.

reply to bradyr
Sometimes with me I see a lot of up and down download speeds depending on what I'm downloading. Sometimes if I download from say EA I constantly on Performance go from 25 Mbps(Couple seconds) to 16(Couple seconds) then dips a little down to 14 or so(Very few seconds) then boosts back up to 25 and repeats that cycle.

reply to bradyr
They're always accurate for me. That speedtest was also for the east coast, not west. You need to be aware of your PowerBoost though and then watch NetMeter to see your actual speed after PowerBoost falls off.
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»www.VAJeeps.com

yeah I didnt check to see where i was connecting to with your link.. my bad there.

I think we can all agree that the bottom line is if the connection is healthy, factoring in powerboost, a typical throughput graph (assuming you're testing against a non-overloaded server and you're "dedicating" your connection to the test.. i.e. telling everyone else to stop doing stuff on the net), your graph should start high, fall off some as powerboost stops, then it should be damn near a rock solid straight line for the duration of the download.

i'll try to post up some TCP stream graphs from wireshark, against some hefty sized downloads (via ftp or sftp), that shows this.

I used to do tcp stream graphs, and look at them all the time when i had dsl and i was on exhausted at&t redbacks/BRAS. you would see the graph go ape-shit (up and down up and down), during prime-time hours. not that clean looking saw-tooth pattern (that looks like throttling, kinda-sorta) and certainly not a smooth straight line.

reply to Crispyfertoo
I started seeing the same pattern (extreme sawtooth pattern) downloading NNTP (Usenet) files about a week ago. All other speed tests on other types of files give me max or near max bandwidth download speeds... I have tested with 30 download threads using easynews and giganews... for about a week now, consistant pattern... peaks at max bandwidth, then down to zero, then back up again.. I have bypassed my router (direct cable modem connection) and no joy.. same results. Also tried using SSL NNTP connection - same pattern. I have been downloading NNTP using Comcast for many years.. never had this issue before. Say what you want, I am convinced that Comcast is doing some kind of traffic shaping/throttling. BTW, what I am seeing is absolutely NOT a powerboost feature.

double post.

reply to Crispyfertoo

reply to inMaryland
from what i've read, comcast's congestion management practices don't do deep packet inspection (DPI). basically it doesnt care [or know] what protocols you're using/ what you are downloading.

now, of course that info could be out of date, and frankly it wouldn't surprise me if P2P traffic, for example, was a "priority target" over some other traffic, if you are on a congested node or otherwise...

also, it would be sweet to see some "evidence" of comcast's congestion management in practice...like show me some tcp graphs.. what does the data stream actually look like? ramp up then get knocked down, rinse and repeat (saw tooth) or is it ramp up, then get knocked down and stay down (capped) for the length of the download...

reply to Crispyfertoo
That looks like normal TCP behavior...

reply to Crispyfertoo
Some more good charts for you to explain this pattern:

So when do we get per-service-flow RED enabled to maximize bandwidth by throwing packets away?

(»en.wikipedia.org/wiki/Random_early_detection)

reply to Crispyfertoo
That looks like speed boost. They give you a couple of minutes of increased speed to tease you then it goes down to the speed you paid for.

That's not how it would look..

reply to bradyr
posting TCP graphs is a very good idea... I will do so.

reply to Crispyfertoo

entire stream

powerboost falloff

reply to Crispyfertoo
Test with this linux torrent. It is a guaranteed ultra fast torrent.

If it downloads normally it's not Comcast.

»btguard.com/test.torrent

Dave
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I may have been born yesterday. But it wasn't at night.