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Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

vCable peak-time congestion




On vCable in Montreal, 60/10 tier, with an SB6120 modem. Ever since the service was activated, I've been noticing slowdowns during peak time. Sometimes it doesn't slow down at all, sometimes it slows to 30-40 Mbps, and other times (like right now) it slows down to single-digit speeds.

It's bad enough that Netflix streaming at full quality isn't possible, I was trying to watch something a short while ago and it kept bouncing around bitrates near 0.5 megabit.

Speeds are fine off-peak. To confirm it's not the test server (which was Nexicom in TO), I did another test to eBox MTL and got ~10 Mbps, which is still a big slowdown.

TSI Andre
Premium Member
join:2008-06-03
Chatham, ON

TSI Andre

Premium Member

Hey Guspaz,

I checked with our NOC team and there should be nothing on our side of things causing this. Is it possibly local? Want us to open a ticket?

Cheers,

Andre

Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

Congested node is what I'm thinking. I wonder if it could also be related to using a 4x1 modem instead of an 8x1 modem? Videotron's site qualifies me for up to 200 megabit, which implies they're using more than 4 channels on my node.

Before opening a ticket, next time it happens, I'll do some basic troubleshooting (rebooting equipment and such things). If the problem persists, I'll let you know.

TSI Andre
Premium Member
join:2008-06-03
Chatham, ON

TSI Andre

Premium Member

Sounds good.

Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

So I spent some time on the phone with TekSavvy tech support last night. We tried everything we could think of to debug the issue: laptop directly to modem, different ethernet cable, factory reset the modem, reseat the coax, etc. Nothing helped, with speeds sometimes turning up good results (58 Mbps once even), but also randomly turning in results in the 20s or lower, or in the 30s and 40s...

Right now it's particularly bad, my tests are all coming back below 10 megabit (I just did a test and got 7.91 down, 10.55 up).

I tried to get line stats from the SB6120, but it's hard, because shortly after the modem syncs, it stops responding to web requests on 192.168.100.1.

I tried to get a snapshot of the signal before that happened, by connecting my laptop, disconnecting the coax, rebooting the modem, loading the signal stats page, and then refreshing it constantly while I plugged the coax in.

The signal to noise ratio seems OK (34 dB), the modulation seems right (QAM256), and the power level seems OK, if a bit high (9 dBmV)... But I never saw more than one channel.

I tried it twice, it would always display only one downstream channel before the page stops responding.

Now, it's possible that I ought to get a new modem, since the SB6120 is a 4x1 modem, and the 60 meg tier is rather on the high end for that, but it seems like that shouldn't explain speeds that sometimes drop to the single digits.

Andre, could you see about maybe opening a ticket with Videotron for them to check the line stats from their end, and verify that they've got me on the right profile and such? Or should I just buy a DCM475?

TSI Andre
Premium Member
join:2008-06-03
Chatham, ON

TSI Andre

Premium Member

I have asked one of my guys to take a look and see if we can open a ticket first before we replace the modem.

TSI Kris
Premium Member
join:2013-11-18
Chatham, ON

1 edit

TSI Kris to Guspaz

Premium Member

to Guspaz
Hey there!

I looked over the info from the troubleshooting last night, but there's no clear cause of the problem here. Based on what you're saying, the signals are a little... closer to the edge than I'd like. I'll get in contact with our vendor before I had home for the morning to have that looked into. Wouldn't be my primary suspect for an intermittent issue like yours, but it never hurts to be safe. Doesn't help that we can't access the web interface when it's connected, but so be it.

If they don't see anything this morning, I'll also give them a shout when I come in tonight, since that's during peak hours (10PM).

As for the possibility of the modem being the problem? Not impossible, I suppose, especially if there's lots of people around the area that are also using 4 channel modems. I wouldn't put my money on it though since it's a rather drastic slowdown.

When it pops up again, could you shoot us a message over in »/fo ··· avdirect with a trace route and 50x pings to www.google.ca the next time you see the slowdown, as well as provide your IP and Gateway? That way we'll have a bit more info to go on and show to the vendor if required.

EDIT: Had a chat with our vendor for the area (opened early this morning it seems) but they didn't see any problem with the signal over the last week, so we can safely rule that out. So, if you could give us a shout with the trace route and pings above, that'd be great and very helpful.

Thanks,

TSI Kris

Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

Sure, I'll do that as soon as the problem manifests itself again. Right now I'm getting full speeds (62.11 Mbps downstream), which is consistent with the slowdowns only occurring during peak times.

TSI Kris
Premium Member
join:2013-11-18
Chatham, ON

TSI Kris

Premium Member

Sounds good, we'll be awaiting the results.

Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

Direct forum post made
Guspaz

Guspaz

MVM

Gotta admit, a lengthy reply asking me to perform a laundry list of troubleshooting that I already pretty much did on the phone with the tech support rep wasn't the sort of reply I'm likely to be terribly enamoured with...

TSI Kris
Premium Member
join:2013-11-18
Chatham, ON

TSI Kris

Premium Member

Sorry about that, looks like there was a little bit of a mixup. I've responded to you now!

Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

A follow up for the general public, the issue was resolved by swapping the SB6120 modem for a DCM475 modem. Either the SB6120 has gone bad (it predates TekSavvy launching cable service), or the extra channels of the DCM475 (8x4 vs 4x4) got around a channel congestion issue. Speeds now appear to be stable at the expected speeds for a 60/10 line.

It actually makes sense why the initial 4 channels might be congested in my building. There are ~350 apartments, and Bell doesn't service the building beyond the basic 5 meg speed. Videotron, meanwhile, offers up to 200. So the vast majority of tenants probably use cable Internet, which would make it pretty easy to get congested depending on how many nodes Videotron serves the building with.

Furthermore, 8-channel service was only just launched in the building maybe a month or two ago, so before that I think Videotron actually used only 3 channels (not even 4), and now they're using 8, and anybody on the older modems are all stuck on the first three or four.

jmck
formerly 'shaded'
join:2010-10-02
Ottawa, ON

jmck

Member

if that were the case then rebooting the modem would cause it to get new channels I think and you'd sometimes get better speeds.

Guspaz
Guspaz
MVM
join:2001-11-05
Montreal, QC

Guspaz

MVM

Would it? Perhaps it's just how Kaphyr reports it, but he's got the channels tagged for which are which. Does it necessarily follow that with 8 channels available, 4-channel modems would dynamically get the least-congested channels?
InvalidError
join:2008-02-03

InvalidError to jmck

Member

to jmck
said by jmck:

if that were the case then rebooting the modem would cause it to get new channels I think and you'd sometimes get better speeds.

With dynamic channel switching, modems can switch channels on-the-fly between any channels within their tuning windows that belong to the same serving group.