VDSL Performance & Tuning

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933 posts

Ultimate Geek

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Reply # 698190 8-Oct-2012 23:04
F--K ME that RFI setting is dodgy!! It's so inconsistent! I can only get it working occasionally now! Reboots, power cycles, resetting it to 1; none of these seem to be working now. I can't get it working properly on ANY of the RFI settings now!! It's SO FRUSTRATING!!! An alternative explanation is that the RFI setting isn't doing anything and that some other factor is coming into play here, but TBH, since I've seen multiple 8+hr runs with RFI on where I get 0.5 CRCPM or less, where previously I'd been consistently getting 8+ for weeks on end with RFI off, I'm reluctant to settle on this conclusion. Is anyone else willing to do some testing with RFI to confirm if we're all hallucinating or not? Stevehodge - your testing was interesting, but I think most of your changes were due to SNRM increases vs any difference with RFI.

varix

90 posts

Master Geek

Reply # 698191 8-Oct-2012 23:06
Judging by the variations I am getting in sync rates and errors just from simply rebooting the modem I would say you could be having the same issue. I am finding it very hard to nail down exactly what is causing the variations.

varix

90 posts

Master Geek

Reply # 698439 9-Oct-2012 14:38
Is higher Signa to Noise Ratio better than lower? I watched my downstream SNR go from 12 all the way down to 2 over the course of about 24 hours. Very strange. Called Snap today and they are sending a chorus tech to take a look. Fingers crossed I am not liable for a $270 fee!

stevehodge

200 posts

Master Geek

Reply # 698449 9-Oct-2012 14:45
Stevehodge - your testing was interesting, but I think most of your changes were due to SNRM increases vs any difference with RFI. I always left SNRM to the right when I was trying the RFI options. I didn't see any improvement with RFI either one or two notches down (what we're calling RFI 2 and RFI 3). I didn't try RFI 4 or RFI 5 though. SNRM down 2 notches was the only thing that made a difference for me.

stevehodge

200 posts

Master Geek

Reply # 698457 9-Oct-2012 15:10
varix: Is higher Signa to Noise Ratio better than lower? I watched my downstream SNR go from 12 all the way down to 2 over the course of about 24 hours. Very strange. If you're talking about the SNR reported on the DSL tab, that's actually SNR margin. It is a measure of the SNR that has been reserved to allow for unexpected noise on the line. There is a target value of 12 set for this by DLM. So a value around 12 means everything is normal and the line is not experiencing unusual noise. A value of 2 is very concerning IMO - I believe if this reaches 0 the connection will fail. A consistently falling value seems weird to me, I'd guess that would indicate that noise is consistently increasing on the line. I'm not sure what would cause that. Modifying the "intended SNR" setting on the line settings tab will increase the target by 1db for each notch to the left. This has two effects: it reduces errors (there is more headroom to handle noise) and it will reduce sync speed (because less of the available SNR can be used to transmit data). We've been using this to try to reduce our CRC errors as we believe that CRC errors need to be under about 0.25 per minute to stay on DLM-1. The actual SNR is shown on the spectrum tab.

SamF

933 posts

Ultimate Geek

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Reply # 698757 9-Oct-2012 21:56
@sidefx: Yeah, I'm running double NAT. People seem to bag this kind of setup hard, but I've run it for years with ZERO issues (performance or otherwise)! IMO it's the easiest and most robust configuration for this kind of setup.

varix

90 posts

Master Geek

Reply # 698797 9-Oct-2012 23:20
Cheers Steve, here is a picture of what it has been doing since its most recent sync. Cant wait to see what Chorus come up with as a solution to these issues I am having. Or what is actually causing them. I think you are right as this will keep decreaing and eventually the modem just looses sync and I have to reboot it.

helis

87 posts

Master Geek

Reply # 698944 10-Oct-2012 10:43
I now have my CRCPM down to 0. It's cost me 6Mbps off my sync speed though. That will have to do until I get the new cat6 cable run. I figured moving the SNR to its max stability was the way to go. This way when I move to DLM1 I will have the best chance of it being stable than I can tweak the SNR from there.

sidefx

1148 posts

Uber Geek

Reply # 698963 10-Oct-2012 11:08
@SamF: Hmm.. maybe I should give double NAT a try. I game (sometimes hosting) and use vpns for work a bit and I just don't want to waste time figuring out issues in the event it does cause problems though. That RFI setting looks like a pain! I'll try retest mine in the next couple of days to make sure it wasn't just a blip. It seemed pretty consistent though on my line in that as soon as I put it up a notch errors increased 10 fold and then when I put it back down they went back down more than 10x. As mentioned above my process now for ensuring settings changes actually "take" on the Fritzbox is: unplug incoming phone line, make change via web interface, soft restart (via fritz web interface), when that's done power cycle the fritzbox, then check setting is still showing as I want and only then do I plug the phone line back into it, heh. @varix: Yeah, will be interesting to see what Chorus find! @helis: Wow, it was looking pretty low before but a real zero is nice! Let's see how DLM treats you know. @SamF: Hmm.. maybe

varix

90 posts

Master Geek

Reply # 699133 10-Oct-2012 15:06
So the latest is that Chorus wont come out onsite unless I have a splitter, Snap say that it is a new policy that Chorus have. Chorus will install a splitter for $400. Meanwhile, this morning I went through a stage where my modem would not sync at all. I restarted about 15 times and would get sync if I was lucky for about 30 seconds then it would drop off again. It was syncing up at around 30mbit down and 1mbit up. Soo, I forgot about it for an hour and came back and tried again. And it synced up at 45mbit down and 10mbit up! What the hell right?! I have restarted twice and it is still picking up a solid speed. Not sure if perhaps Snap or Chorus have found something and fixed it or if its just being its usual self and will turn to s**t later. Here is a run down of the current situation, note that my attenuation has decreased to 2db from 3db. My only concern is that after a while the FEC errors seem to spiral out of control. Earlier on while at this sync rate before I restarted again it was up to about 100,0000 in the last 15 minutes. One other interesting thing I have discovered is that every time I get a decent sync rate the Pilot reference is in the first block of Downstream, and every time I get a crappy sync rate the Pilot reference is in the second block. Also the RFI spike that is on my line was sitting just over 256 on the Carrier and it is now sitting at about 128.

SamF

933 posts

Ultimate Geek

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Reply # 699145 10-Oct-2012 15:22
So is your line now effectively straight from the street to a single phone jack where you have your VDSL plugged in? Or are there other jacks / devices plugged into the line as well?

sidefx

1148 posts

Uber Geek

Reply # 699147 10-Oct-2012 15:24
$400 for a splitter is a bit crazy; you can probably do it yourself for around $60... Can you put up a photo of the inside of your ETP looks? A decent test would be to connect your modem direct to the incoming pair at the demarc (with nothing else connected) and see how that goes.

varix

90 posts

Master Geek

Reply # 699159 10-Oct-2012 15:51
@SamF My line has always been connected straight to a single jackpoint that feeds direct to the ETP via a single CAT5 cable. All other jackpoints have been deleted from the wiring. @sidefx Yeah I figure thats what I will do, I have found VDSL splitter from computer dynamics for $20. I was thinking about doing that with the ETP. Just didnt want to mess with the wiring inside it too much. Here is a picture of the inside of it. Is it just me or is it strange that Blue and White have been paired together?!

SamF

933 posts

Ultimate Geek

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Reply # 699160 10-Oct-2012 15:53
Ok, if you don't have any other jacks connected then a splitter is pointless and won't help with the line issues. I'd ring Snap back and explain that you have one connection in the house (all others disconnected) straight to the incoming line.

varix

90 posts

Master Geek

Reply # 699165 10-Oct-2012 15:57
Snap are aware of the fact I have a single jackpoint and are fighting with Chorus about it. Sounds like Chorus dont care how many or how little jackpoints you have they still say you must have a splitter.

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