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Author Topic: Line 1 upstream cycle now  (Read 1870 times)

Weaver

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Line 1 upstream cycle now
« on: January 18, 2020, 12:52:18 PM »

Recap: My line #3 has for a long time had a problem with the upstream SNRM, which drops sharply for approx half the day and then sharply shoots back up again. The height of the drop is 5.7dB and dropping from 6dB like that isn’t funny so you have to hope that it’s in the ‘low’ state when initiating a retraining of the modem, so that later it will shift up to a very high level harmlessly. I have tried setting the upstream target SNRM to 9dB to help deal with the case of a retrain when at the high level (of the target) which is either 6dB or 9dB but the latter being safer as a drop from 9dB isn’t tooo bad.

This really really slows the upstream down, by 25%, eg 500k->420kbps Line 3.

But now I’m seeing a similar thing with my line 1. It started fairly recently, can’t say when exactly. The drop is not as high so it isn’t quite such a disaster. There will be the same thing; if there is a resynch at the wrong time then the upstream will be really slow.

The other badness is that if the speeds change dramatically then the Firebrick’s egress / tx rate limiter values assigned to each modem by kludgey external software (which does not run automatically in timely fashion) will be wrong so the fraction of total upstream traffic assigned to each modem will be be wrong too, as it will have  been set according to out-of-date upstream tx / egress speed capability values.



Line #3:





Line #1:




Digressing seriously, for the moment. This makes me wish there was some kind of local site info broadcast/multicast system, I may have written about this before? DHCP does some of this effectively and a radical expansion of DHCP would seem to be the way to go. It would be better from the point of efficiency and robustness though if there were a system based on multicast and one that supported both IPv6 and IPv4. DHCPv4 isn’t suitable because of IPv6-only clients. If multiple multi casting info servers could gather information and then distribute it, also synchronising data so they all carry a complete copy, and with the capability of electing a new master if a machine is seen to have died or is not performing its function. Maybe the other machines could take it in turns to poll the master, asking it questions that require some very small amount of intelligence in the response. If clients subscribe to multicast then that would cut the load of noise imposed on the network dramatically.

Such an info server system could tell clients all kinds of things about the local site; such things could enhance TCP’s behaviour by tuning.

In the present case modems could be queried and the speeds converted into tx / egress rate data - as IP PDU rates - for routers. But most importantly, modems’ resynchs could be detected and when modems’ speeds change then routers could be informed with a real-time event with new upstream / tx speed values as IP PDU rates.
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burakkucat

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Re: Line 1 upstream cycle now
« Reply #1 on: January 18, 2020, 03:22:33 PM »

It really does seem as if there is some source of interference (located somewhere between your modems in Heasta and the DSLAM in Broadford). The recent re-working of all of the Heasta - Broadford circuits, subsequent to the lightening damage at the end of 2019 (and more recently), appears to have placed your circuits in closer proximity to the interference source. (Whatever that may be.)
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Weaver

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Re: Line 1 upstream cycle now
« Reply #2 on: January 19, 2020, 11:52:05 AM »

There is a vaguely similar phenomenon on line 2, but the height is not as great and it isn’t a 24-hr regular period, there is an irregular pattern. At the moment I am not seeing it on line 2 though, which is strange.

Over the last 24 hours I’m not seeing the regular 24 hour pattern on line 1! So perhaps it wasn’t as regular as I thought.
« Last Edit: January 19, 2020, 11:56:36 AM by Weaver »
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niemand

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Re: Line 1 upstream cycle now
« Reply #3 on: January 19, 2020, 04:29:25 PM »

As a note to your digression A&A could just fix their software so it updates shaping parameters promptly.

They get sent them on each sync event. Stuff on the LAN has no need to know and shouldn't care to know what's going on with the DSL, not its problem.

Your Firebrick? No reason why A&A can't inform it when BTW / AN Other update them, which they need to for downstream shaping purposes.

That is probably a conversation best had elsewhere but, either way, network telemetry like that has no business outside of the network edge as delineated by IP or PPP, depending on encapsulation.
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Weaver

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Re: Line 1 upstream cycle now
« Reply #4 on: January 21, 2020, 07:20:30 PM »

Now the line 1 cycle has gone away. It was a one-off - I was wrong.  :-[
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Alex Atkin UK

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Re: Line 1 upstream cycle now
« Reply #5 on: January 21, 2020, 07:35:52 PM »

Honestly its a nightmare, considering how long and exposed your cables are, they could be picking up interference from miles away. :'(
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Weaver

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Re: Line 1 upstream cycle now
« Reply #6 on: January 21, 2020, 11:43:58 PM »

The odd thing is this stuff is low frequency only and as far as I can see has to be from a source in Broadford or Harapul which is switched on and off. Long distance emitters such as radio stations do not have that time on/off pattern and I don’t know about what kind of source might have a low frequency so as to fit in the upstream band only.

Turning to downstream for a moment, I think I’ve once identified a noise distribution notch that comes from a radio station in the Black Isle (which is a peninsula, despite the name, just immediately north of Inverness) on the other side of the country, the east coast, and further north. That’s 60-75 mi away. I also suspect I might be getting noise from Tiree airport, Benbecula Baile a’ Mhanaich airport or even Stornoway airport. Those are very weak suspicions though. But the point is that the Black Isle source is spot on in frequency terms and I think very convincing, so it would seem that you can indeed pick signals from 60 miles away using a 7300m long antenna.

There are no neighbours and no buildings between Harapul and the house. But there is half a mile of housing and human and electrical activity in the first half mile of the the run, which is from the NSBFD exchange in the centre of Broadford to the point at the Claymore restaurant on the main road, in the suburb of Harapul, where the cable run takes a turn off to the south and head for Heasta. The first couple of hundred metres of that road also has houses and then that’s it, just moorland with no buildings all the way. I make it approx 1470 m of civilisation from exchange to the last house, and then ~5927m from there to the house, or ~7400m in total. Earlier attempts at measuring on the map came out with 7300m. (As discussed earlier, there are problems associated with the map measurements in that you can end up with uncertainties in how exactly to deal with wiggles in the road. These methodology uncertainties can inflate or decrease the estimate if total length obtained.)

I would assume that it’s something very local which is getting turned on and off. Why it doesn’t affect all lines in the same way is inexplicable; some lines are free of it - why on earth is that ?

Can there be a fault in line three that makes it exceptionally prone to LF interference pickup only?

That’s the only kind of half explanation I have; at least that would explain why all lines aren’t the same.

I also have no candidate explanation about the timing of line three.

I have reported the low performance upstream of line three to AA but they aren’t realistically able to do anything about it; not unless there’s some kind of test procedure. Also BT doesn’t seem to have any kind of standards for upstream. Just saying it’s bad because it’s not the same as the others isn’t an argument, even though it’s just obvious and stands it reason. You could say that line 3 is normal and the others are abnormally good. It is however also bad news because of the variation alone; the noise variation is not something that the existing system can cope with well.
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Alex Atkin UK

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Re: Line 1 upstream cycle now
« Reply #7 on: January 22, 2020, 03:09:32 PM »

Did you ever get a line length estimate from Openreach?  Would be curious to see how that compares to the map.

I noticed in one of your flickr photos it looks like you have two drop wires from the pole?  So you'd think that its possible one might pick up interference the other does not, but then it should impact two lines?

So one and three both being impacted kinda makes sense, but it differing or vanishing completely off one of them is utterly bizarre.

All I could think is something mundane like a slight nick in the sheathing of the cable that is exposing one pair more than the rest?

Then again, at the exchange end all bets are off, its going to be in a big bundle and all four lines could be nowhere near each other there, causing some discrepancy.  My two relatively short lines to the cabinet differ quite a lot.  Seeing how they joined two cables recently in the local ducting, it doesn't look like theres really any consideration for crosstalk issues when doing it.
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Weaver

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Re: Line 1 upstream cycle now
« Reply #8 on: January 22, 2020, 07:25:22 PM »

How does one get a line length estimate?

(You can actually see the telephone cable, lying on the rocks in some places so fairly confident about its route.)

I do have two drop wires, but I can’t see any possible difference in them; they run together, and in addition, line 3 and 1 are the two pairs in the same drop cable but they don’t show the same upstream cycle.
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burakkucat

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Re: Line 1 upstream cycle now
« Reply #9 on: January 22, 2020, 08:40:26 PM »

How does one get a line length estimate?

Correct me if I'm wrong but I believe Black Sheep looked at the network records for you, some years ago.
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Alex Atkin UK

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Re: Line 1 upstream cycle now
« Reply #10 on: January 22, 2020, 09:57:53 PM »

Pretty sure A&A should be able to get them from the Openreach portal, unless things have changed since 2014 (would not be surprised).

As I recall, it was someone from Zen who got mine.  They did it while trying to get the tags off my line to migrate to VDSL.
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Weaver

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Re: Line 1 upstream cycle now
« Reply #11 on: January 22, 2020, 11:35:57 PM »

@burakkucat Ah, it’s that that we’re looking for.
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anything