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andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL

[Speed] Weird upstream speed issue

I ran into a weird upstream issue a few weeks ago (the same day dslreports crashed.)

I had a weird issue where copying files through my work VPN from me to work were unusually slow. Looking at the router, I could see it constantly pausing. It was even weirder in that some servers were more affected than others. My upstream and downstream signal were fine and no different than before, and speed tests were also OK. My modem (SB6120) was on channels 8/1/2/3. I had suffered through this about a year ago, but it cleared up. This occurred after a modem reboot. My work computer, which is part of a domain, was affected. My home computer, which is standalone, wasn't affected much, even copying over the same VPN.

After some testing, I tried the VisualWare site and their quality test. That showed some weird issues, like duplicated ACK's and lots of retransmits. After some testing, I rebooted the modem a few times until I ended up on another downstream set (2/3/4/5). The quality tests were now much cleaner, and copying to work through the VPN was fine. The upstream channel did NOT change.

I can only assume that there is either something wrong with channels 1 or 8, or it doesn't like that big wraparound or out-of-order channels? I'm guessing upstream was slow as the copying (normal Windows COPY and similar) was getting confused by the duplicated packets or something. I'm not certain why the work computer was affected more, other than maybe some extra security information was getting lost and it had to keep re-verifying?

Basically a long message, but a note that upstream issues may not always be caused by problems with your upstream signal.

nysports4evr
Premium
join:2010-01-23
kudos:1
Reviews:
·Comcast
I have frequently experienced strange upstream issues like you describe, not only low bandwidth on the upstream side but packet loss, etc, and after resetting defaults and rebooting the modem via the web interface allowing it to completely re-initialize fixes the problem.

andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL
Why is that when things are going fine, that things get screwed up?

I came home today to a total outage. There was a Comcast truck in front (I'm in an apartment.) He was still inside the truck. It appears that the landscaping people had cut some cables, although they were here Thursday, unless they did some work while I was out. When he was fixing the cables, he hooked mine up wrong (we are still physically wired with the old A/B setup.) He put a signal generator on my line and found the correct cable to set up.

Of course, my modem then picked up something like 5/2/3/8. When I tried a quality test, I had all sorts of weird errors. I tried a reboot, but got the same. I did a reset then a reboot, and now am on 1/2/3/7. So far, the quality test is OK, showing only one duplicate ACK.

So there is either something wrong with channel 8, or the modem doesn't like non-sequential frequencies.

andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL
reply to andyross
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Some pics of the new mess.