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Since yesterday any file I try to download from any host start downloading ok (at >1mbps) but after a few seconds the speed start to decrease down to 10kbps.

I use a mobile modem (huawei) and I connect to a wcdma network.

What could be happening? I use kaspersky, and I checked the Network Monitor and I don't see any weird process using bandwidth.

I did a test on and I got 1mbps of download but that speed doesn't hold more than 1 sec when downloading files.

What other tests can I run? Recommend me some app to monitor the traffic to see if I have some malware or see where my bandwidth goes.

I use chrome, firefox and flashget to download, all show the same problem.

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It's not unknown for ISPs to "burst" downloads like this, so that you see the web page come up quickly, but throttle the speed when the download persists for more than a few seconds.

It's also not unknown for them to disable the throttling when connecting to known speed test sites. Try quite a few of them, and maybe you can catch your ISP off-guard.

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@#&%$ isp! Thanks for the info. – user38070 May 23 '10 at 16:59
It would be worth asking your ISP if they've just started doing this, since you say this started yesterday. If not (and you believe them) then at least you'll know to be looking for a local problem. – JRobert May 23 '10 at 17:02

IPerf is a simple command-line tool that's used quite a bit in the networking industry because it's great for more reliable measurements of network speed than you're likely to get with a file copy or HTTP download or video streaming. You can do a simple 60-second TCP test like this:

One machine is the IPerf server (in your case, your WWAN machine):

iperf -s -i 10

The other machine is the IPerf client (maybe a machine on your home or work broadband connection):

iperf -c $IPAddrOfIPerfServerBox -i 10 -t 60

Some advantages to running IPerf:
- Connecting to your own machine, can't be gamed by ISPs that don't throttle bandwidth to known speed test sites.
- Fast native code, as opposed to online speedtest tools that run in Flash or Java or JavaScript.
- Does pure TCP (or UDP) data transfers, without the overhead of, say, a remote volume mounting protocol like SMB or NFS or AFP (beats the heck out of timing a file copy).
- No disk I/O, so it's not constrained by disk speeds.

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