Strange changes in ADSL Noise Margins

Forums › Spark New Zealand (including Skinny and BigPipe) › Strange changes in ADSL Noise Margins - What is going on???

res

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#247747 20-Feb-2019 15:13

Hi,I live in a rural site some 4.5 k away from the DSLAM in the nearby Wairarapa town. No surprises we are stuck on ADSL, even fixed wireless doesn't look like a runner.

That said, I've installed the in-wall splitter, and placed my ADSL modem (Tecnicolor TG789vn v3 on generic firmware) close to it. In this config, it consistently connects at around 8.5Mb/s down and 1.1Mb/s up, and clearly the speed is negotiated to achieve a 6dB noise margin both down and up. I use this modem as it has a Broadcom chipset matching the DSLAM, plus it gives near real-time display of speed and noise margins.

Last December things went strange. Speeds sagged to <7 down and about 0.9 up, with a massive 12dB noise margin down and up, no matter how many times I reconnected. I listened to the fixed phone, no funny sounds on the line or significant new electric fence ticks. I swapped in an older TG585v8 and it connected at the same speeds/margins. So, not the line, not the modem?

A week later nothing had changed and I was thinking I'd need to call Spark faults and somehow ????? get the person on the other end to understand the issue. I could not see that ending well. Someone talking noise margins to their under resourced, under paid, limited training help desk?

Then I again looked at where my connect speeds were. They had improved! Clearly we were now negotiating for an 8dB margin up and down. A few days later and we were back to normal speeds and 6dB margins. This was weird, but OK things were normal again......

Come Feb 2019 and the up speed only has dropped, it is negotiating a 12dB margin, while the down speed is fine still targeting 6dB. As of the last week or so, we've been steady with down normal, up still a little low and now 8dB margin.

Does anyone have any idea what Chorus (I assume) are doing? Is someone tinkering with DLAM settings? Doing DSLAM software upgrades?Any other suggestions for diagnosing this?

Thanks for any ideas/info

RES

wratterus

1687 posts

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#2184399 20-Feb-2019 15:15

Sounds like ddDLM doing it's thing - possibly there is a small line issue somewhere. Have these changes coincided with a lot of rain or anything like that?

Have you tried a new/different modem for a few weeks to see if it will stabilize at the lower SNR margin? Wouldn't surprise me if that modem was the issue.

hio77

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Lizard Networks

#2184410 20-Feb-2019 15:38

This is absolutely ddDLM doing it's thing.

it will adjust line profile in order to balance stability and speed.

If your rebooting your modem tons, that would encourage it to suspect your line is faulty.

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hio77

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Lizard Networks

#2184412 20-Feb-2019 15:39

Most of the DSLAM's there are vectoring enabled too, so your better off on a modem that supports G.INP and Vectoring

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RunningMan

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#2184442 20-Feb-2019 16:51

res:[snip]Last December things went strange. Speeds sagged to <7 down and about 0.9 up, with a massive 12dB noise margin down and up, no matter how many times I reconnected.

Every time you reconnect, ddDLM thinks there is a problem with the line. It sees all the disconnections, and increases the noise margin to try and get stability on the line. Best not to disconnect unless you really have to.

antoniosk

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#2184449 20-Feb-2019 16:58

or better yet, why don't you call Spark and _not_ presume that the other end will be staffed by someone who cant help. Yes you need to go through front line help desk, but if you keep it simple and straightforward - "my internet was very fast before xmas but now is getting slower and slower", they will escalate to tech support desk, and they can open an investigation case for you using what you do know.

It's interesting that the default listening for ISPs is they are all incapable of helping, before being proved incompetent.

________

Antoniosk

res

18 posts

Geek

#2184470 20-Feb-2019 17:59

antoniosk:

or better yet, why don't you call Spark and _not_ presume that the other end will be staffed by someone who cant help. Yes you need to go through front line help desk, but if you keep it simple and straightforward - "my internet was very fast before xmas but now is getting slower and slower", they will escalate to tech support desk, and they can open an investigation case for you using what you do know.

It's interesting that the default listening for ISPs is they are all incapable of helping, before being proved incompetent.

Don't want to be rude - but have you actually tried your own medicine? Ok it's been a couple of years since I last did, but based on that and the previous times, seriously, THEY ARE CRAP.

Thanks everyone for your ideas. May start looking for a new modem. But vectoring isn't used on ADSL is it, only VDSL?

hio77

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Lizard Networks

#2184486 20-Feb-2019 18:33

Your right on vectoring. I've got a lot on lately and slipped what tech your on.

ADSL still has dddlm working on it.

As someone who builds the assure systems I can say we have plenty of great experiences.
I won't deny that the occasional case can go wrong, but we are all human.
A few years ago things were very much legacy. Tons of improvements and even means that do not require you to call.

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toejam316

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#2184489 20-Feb-2019 18:42

res:

antoniosk:

or better yet, why don't you call Spark and _not_ presume that the other end will be staffed by someone who cant help. Yes you need to go through front line help desk, but if you keep it simple and straightforward - "my internet was very fast before xmas but now is getting slower and slower", they will escalate to tech support desk, and they can open an investigation case for you using what you do know.

It's interesting that the default listening for ISPs is they are all incapable of helping, before being proved incompetent.

Don't want to be rude - but have you actually tried your own medicine? Ok it's been a couple of years since I last did, but based on that and the previous times, seriously, THEY ARE CRAP.

Thanks everyone for your ideas. May start looking for a new modem. But vectoring isn't used on ADSL is it, only VDSL?

Most of the ISPs have smart people nestled away, and they're there to help. It might feel like the help desk isn't there to help, but they're there to filter the "OH I WAS PLUGGED INTO THE WRONG HOLE IN THE FILTER?" from the "Yeah, it DOES seem like you've got a weird issue with DHCP, I guess we'll send out a new router out".

Anything I say is the ramblings of an ill informed, opinionated so-and-so, and not representative of any of my past, present or future employers, and is also probably best disregarded.