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Cable Modem bandwidth degradation (simultaneous up and down loading )

Posted on 2007-04-04
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Last Modified: 2013-12-14
I have residential Comcast cable modem broadband internet with typically 6Mbs download and 300Kbs upload.

When i am uploading(FTP)  a large file, download bandwidth drops to the 400-500Kbs range (less than 10% of upload-idle state).
My understanding was that a cable modem is full-duplex and can deliver (almost) full typical bandwidths simultaneously.
I do have a switch (1000T) in between, but i don't think this is the culprit since at no other file transfer time(combination of directions or traffic) just between computers in our office   does any degradation happen that is not normal(explainable) "sharing" of bandwidth for the files being transferred.
Thus it's not related to processor speed (since 1 computer up and another computer down  slows the download for the down) (Core 2 duo E6600)

Other observation: always when uploading anything to the internet (FTP), web radio hiccups every 2-3 seconds, thus indicating dropped packets due to download bandwidth

Any ideas?   Of course Comcast just says it's my computer, or another time they said they do not guarantee bandwidths (which they do not).

thanks


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Question by:willsherwood
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AndrewCink earned 2000 total points
ID: 18854437
Most likely the issue here is, your upload bandwidth is significantly less than your download bandwidth. What happens, is when you are downloading, you have to still send data back upstream to let the host know you got the last packet successfully and to send more data. If you are using all of your upstream to upload, you are unable to send the packets upstream to confirm the downstream packets are arriving intact. The best thing you could do is try to set up software to rate limit your uploads so that you are not using ALL of your upload bandwidth for data uploads. You need to reserve some bandwidth for connection overhead. Then there should be enough bandwidth left over to handle the overhead of handling other requests related to downloads, requesting downloads, etc.
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by:willsherwood
ID: 18915422
This is likely the situation.
I've been looking over the last week for FTP clients that can do upward throttling without having to always have downward throttled.
might you know of any?
for instance, CuteFTP allows throttling but only for BOTH directions if turned on.

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Author Comment

by:willsherwood
ID: 19415877
perfect answer
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