Speed drop to zero but the connection is fine.

November 9, 2007 8:59 AM

Why does my download speed drop to zero when the internet connection is still up and working?

I have a 10mbit fiber to the home connection that was just installed recently and I've noticed some strange behavior.

I've tried to download the Flight Simulator X trial from the microsoft web site. The download starts out fine and then at about the 20% point the download just stops, immediately drops to zero. Not slowly trickling down to zero, from full speed to nothing.

Here's a screenshot that shows the problem. This was taken when the PC was in safe mode. No firewalls, connected directly to the "transceiver" (PC had a public, routeable IP address). The transceiver is a Allied Telesyn AT-iMG646BD-ON

It's totally repeatable and it stops at the same point each time I try it. I've let it sit for a few hours with no change. Eventually it will give a timeout error message. I've noticed this with much smaller files as well, it will download up to point and then stop. If you cancel the download and attempt to start it again, it won't even start downloading.

The really strange thing is when these downloads stop I still have internet access. I can still bring up web pages and streaming audio that was running before the download continues without a blip.

My first thought was some sort of transparent proxy/caching problem (on the ISP's side), but using online tools like ProxyJudge and proxyscanner don't detect any proxy info in my HTTP headers. Not sure how conclusive that is.

Here are some things I have done:
- Updated NIC drivers
- Tried a different NIC
- Tried a different PC (laptop)
- PC in Safe Mode, connected directly to transceiver
- Switched to OpenDNS servers

This is a XP SP2 machine, all patches applied. Dynamic IP from the ISP with about a three day lease.

The only things I haven't tried are
A) running a new line from the tranceiver (in the garage) to the office (about 50 to 75 ft).. Also the terminations at the transceiver end looks a little ifffy. Could a cabling problem cause this?
B) Ubuntu boot disk.

Snooping on the line shows that HTTP payloads are coming in fine and ACKs are being sent back, the last packet in the conversation is an ACK from me then nothing further from the remote host.

Ironically, bittorrents usually work fine. Speeds do fluctuate but never drop completely off.

My guess is something is misconfigured or broken on the ISP side. There is already a call into the ISP and I am waiting to hear back (not holding my breath).

Let me know if you need any additional info. Any ideas/suggestions appreciated.

Thanks.

posted by banshee to Computers & Internet (7 answers total)

Could there be a problem on Microsoft's end? Like the trial file is broken?
posted by Lentrohamsanin at 9:05 AM on November 9, 2007

This exact thing happened to me. Not sure what happened but AT&T fixed it. This is definitely an ISP issue, not a local issue.
posted by damn dirty ape at 9:28 AM on November 9, 2007

Try reducing your MTU slightly, from 1500 to say 1400. But yeah, it's probably an ISP issue.
posted by kindall at 9:42 AM on November 9, 2007

Feels like an ISP issue -- something at your ISP is sensing a prolonged connection to a single host and cutting it. It makes sense that BitTorrents work, too, since these tend to be a lot of shorter connections to multiple hosts, and if your ISP kills one of the connections, your BitTorrent client just sets it back up and/or moves on to another computer that's seeding your file.
posted by delfuego at 11:14 AM on November 9, 2007

Is your service provided by Comcast?
posted by Aquaman at 11:56 AM on November 9, 2007

Response by poster: Not Comcast, Surewest.

delfuego: I'm thinking the same thing. Does anybody have any experience with a server/router that would perform such a function? I assume this would be an off-the-shelf item rather than something home-brewed. Maybe some sort of over-zealous virus/malware filter or something?

Thanks again.
posted by banshee at 1:07 PM on November 9, 2007

A similar thing happens at work with large files. Yet our work connection will be a lot different to yours. my computer > squid proxy > router > microwave to our provider to their squid proxies, through their network and then an internet routable ip on their edge. I always figured it was some unfortunate feature of the whole setup.
posted by browolf at 3:11 PM on November 9, 2007