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Author Topic: Erratic line behaviour after remote resync  (Read 9869 times)

Chrysalis

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Re: Erratic line behaviour after remote resync
« Reply #180 on: April 26, 2017, 03:12:18 AM »

not going to newt as I want to keep my current sync speed.  It will very likely sync at around 6.3db tho and around 68mbit speed.
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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #181 on: April 27, 2017, 01:28:04 AM »

. . . without a break in service. The latter statement does not seem possible but it is the case. (It can be done with extra jumpering and implies that, for a time, there will be double jumpers linking the "left-hand side" with the "right-hand side".)

Yes, that is indeed what happens. I thought this was what Openreach refers to as being T'ed (or is that Tee'd?).

It tends to happen when OR are working on many lines, without anyone reporting a fault, and is done to keep service in place when a break in service is not expected.

(OT: There was a brief scene in the "Dial B for Britain" programme, where they cutover a new exchange. A row of engineers pulling whole columns of breakers in the MDF, so lines were instantly changed from old exchange to new one).

the last 24 hours SNRM plot from Kitz' circuit. Notice the difference from what I described, above? The two "ruler-straight" lines have now been replaced with those that show a 24 hour cyclical effect;

Ah, right. I was looking at kitz' own pictures, where the cyclic effect was the 5 min 35 sec. But yes - strange for a line to change from having no diurnal changes to having a significant one. Something has opened the line up to EMI that it plainly wasn't susceptible to before.
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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #182 on: April 27, 2017, 01:35:41 AM »

Already been there.  It appears to affect U2, D1, D2, D3.   See attached graphs below from when I was doing the intensive logging and it shows up very clearly.

Interesting to see the differences, and that band aren't affected equally. I really wanted to see different graphs though - the ones that show the SNRM for each individual tone - the 4th graph in the "Tones" tab in DSLstats.

The swings of 6-7dB in those SNRM-per-band graphs should show up as significant difference between one graph timed when the composite-SNRM is peaking vs one graph when the composite is troughing.

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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #183 on: April 27, 2017, 01:39:32 AM »

I wonder if it could be the result of an overloaded amplifer input stage due to a defect in an AGC circuit failing to stabilise the overall gain. Or something similar. (Whatever any of that may mean . . .)  :-\

 :idea:

....

Oh, wait....


I've no idea what any of that meant  :doh:

I know what the words signify, but I haven't the foggiest what the impact would be on a copper line. It's all that analogue stuff, right?
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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #184 on: April 27, 2017, 01:47:32 AM »

However, the DLM applying banding without INP is akin to increasing the SNRM, still without INP. So I suppose it depends on what the DLM is trying to protect against. If the DLM is trying to increase resilience against sources of constant noise, then it might increase the target SNRM, or cap the rate, which both achieve the same result.

Simplistically, it is equivalent.

However, I think banding is (in a broader sense) considered to be a newer, superior DLM mechanism than increasing the target SNRM, and is described as such in NICC's document on DLM. This might relate back to power settings, and might not fully apply to BT's model.

Alternatively, if it's trying to protect against pulsed noise sources, either isolated pulses, or repetitive (REIN), then it could set INP. Also, it wouldn't surprise me if BT try to avoid any form of INP to avoid the equipment using slightly more electricity from doing all that extra processing.

If BT were that worried, surely they wouldn't have bothered with G.INP, where all that extra processing is turned on anyway?
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ejs

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Re: Erratic line behaviour after remote resync
« Reply #185 on: April 27, 2017, 04:58:45 PM »

I thought retransmission wasn't enabled by default, it's switched on as and when the DLM decides.

It also occurred to be that people can tweak the SNRM (or try to), but mostly can't override a rate cap (well, they can set their own rate caps, but only lower). And that people may not want the extra 8ms or however much latency interleaving adds.

The NICC document (1513) does say (TRA being Tiered Rate Adaptation, banding):
Quote
Simulation has shown that use of TRA for DSM Level 1/DLM has the potential to reduce power
consumption on DSL lines. However, this is one particular aspect of the analysis that merits deeper
investigation using experimental techniques on real equipment in order to better quantify these
potential benefits. This would be a useful area in which NICC could encourage further work.
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burakkucat

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Re: Erratic line behaviour after remote resync
« Reply #186 on: April 27, 2017, 09:56:36 PM »

(or is that Tee'd?).

To me, "tee'd".

Quote
(OT: There was a brief scene in the "Dial B for Britain" programme, where they cutover a new exchange. A row of engineers pulling whole columns of breakers in the MDF, so lines were instantly changed from old exchange to new one).

Ah, so you also spotted the "pulling of the wedges".

Quote
But yes - strange for a line to change from having no diurnal changes to having a significant one. Something has opened the line up to EMI that it plainly wasn't susceptible to before.

So much for a neat and tidy PCP!  ::)
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burakkucat

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Re: Erratic line behaviour after remote resync
« Reply #187 on: April 27, 2017, 10:21:17 PM »

It's all that analogue stuff, right?

Yes, indeed. Otherwise why would every modem(/router) have an analogue front end (AFE)?

[off topic]
Many years ago (about 40 - 45), I was making adjustments and balancing the various inputs to an amplifier system in a church. A very big, resonant, space . . . drop a hymn book from greater than three feet in hight and hear an echo tuned to E flat minor. Having got everything "just so", I went around to each location where a microphone was installed and opened them all to the input mixer. And listened. Very slowly, it became apparent that the system was just on the cusp between stability and oscillation. And then it happened. (Probably a very low frequency rumble, from a lorry passing on the main road, was the trigger.) Rather than the usual feedback howl, the system exhibited a pulsed "woop", "woop", "woop" symptom. Each "woop" was at the same, lowish, frequency and appeared to correspond to the natural resonant frequency of the building. It was a perfectly stable state of pulsed "woops" . . . I could go to any one of the microphones and supply further input to the system, which was reproduced but had no effect on the system's pulsing state.

[off topic 2]
Q) What would you get if you dropped a grand piano down the main pit-shaft of a coal-mine?
A) A flat miner.
[/off topic 2]
[/off topic]
« Last Edit: April 28, 2017, 05:23:13 PM by burakkucat »
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NewtronStar

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Re: Erratic line behaviour after remote resync
« Reply #188 on: April 27, 2017, 10:38:36 PM »

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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #189 on: April 28, 2017, 11:46:23 AM »

Sorry, there was a bit of tongue-in-cheek to that "analogue stuff" statement...

Before I got into software, one of my hobbies was electronics, so I know plenty about analogue electronics. It's just that digital stuff took over, and even now, I can play with embedded systems where the two sides meet - arduinos, pis etc. Working in telecoms, and PCM-encoded speech, you get very involved in A-to-D and D-to-A - and in my early days, that included the signalling too.

However...

I only know enough to be dangerous. The theory of electronics, up to but not including inductance, coils, and resonance. I understand the basics of motors, generators and transformers ... but not the stuff where RF engineers earn their crust.

Because of that, I don't have the skills to deal with analogue when it gets tricky, and isn't working correctly. To troubleshoot properly.

So I would know what an AGC was for, and could describe why it was beneficial to a system (especially to us on the digital side). I might semi-understand the circuit diagram for one, but I couldn't design one, and couldn't begin to fix it if it went wrong.

I went in the direction of TTL, CMOS, logic, bits and bytes instead.

Edit: But I'm impressed by the feedback in the church. Just to prove that analogue stuff can be weird!
« Last Edit: April 28, 2017, 11:48:51 AM by WWWombat »
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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #190 on: April 28, 2017, 11:53:27 AM »

So much for a neat and tidy PCP!  ::)

I don't believe that the PCP itself could possibly be the source of that amount of interference from the re-arrangement.

I am prepared to believe, however, that the PCP work introduced a fault that made the rest of the line susceptible to picking up that interference.

On the other hand, I just admitted that my troubleshooting skills were lacking in this area ;)

[for the avoidance of doubt, I'm talking about the diurnal variation in interference here, not the short-duration variations]
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renluop

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Re: Erratic line behaviour after remote resync
« Reply #191 on: April 28, 2017, 12:10:26 PM »



[off topic 2]
Q) What would you get if you dropped a grand piano down the main pit-shaft of a coal-mine?
A) A flat miner.
[/off topic 2]
[/off topic]

Was his name Stanley?  ;D
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WWWombat

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Re: Erratic line behaviour after remote resync
« Reply #192 on: April 28, 2017, 12:12:20 PM »

I thought retransmission wasn't enabled by default, it's switched on as and when the DLM decides.

You're right, but reality is slightly more complex than that...

It seems to me that BT really want to have G.INP switched on by default, as it offers a very good improvement to lines in general (*).

However, practical problems involving device compatibility means that G.INP has to be turned off by default - because simply syncing (for everyone) is more important than achieving best stability (for 99%).

BT's compromise then seems to be that DLM will turn on G.INP "by default" unless it sees a reason to do something different. Even if DLM isn't yet optimal in this regard.

It also occurred to be that people can tweak the SNRM (or try to), but mostly can't override a rate cap (well, they can set their own rate caps, but only lower). And that people may not want the extra 8ms or however much latency interleaving adds.

It seems to me that, while BT allow a CP to ask for a line to be in one of 3 "stability" states, they are missing the "try not to add latency to gain stability" setting.

The NICC document (1513) does say (TRA being Tiered Rate Adaptation, banding):

That will indeed be the stuff I had seen a while back.


(*) - I've attached two graphs that depict the improvement attained from widespread activation of G.INP.
The two were gleaned from BT without verbal explanations, so you have to figure out the meaning yourself.
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kitz

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Re: Erratic line behaviour after remote resync
« Reply #193 on: June 02, 2017, 12:01:59 PM »

Just a quick update.   Line goes through some periods of stability, but does still have periods where the SNRm fluctuates and the odd period where the Err Secs go into many thousands.
Thought I'd share my observations what the DLM has been doing

1st offence INP3 for 2 days.     (Apr 4 - Apr 6)
2nd offence INP3 for 10 days    (Apr 13 - Apr 23)
3rd offence INP3 for 14 days.    (May 18 - Jun 1)
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burakkucat

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Re: Erratic line behaviour after remote resync
« Reply #194 on: June 02, 2017, 03:07:46 PM »

I have been "looking in" on your circuit's behaviour, once every day, and in general it seems to have stabilised. The diurnal change in the SNRM is no longer seen. However the "tail end droop" of the Hlog plot remains and the QLN plot still appears to be "fuzzy" (or "furry").
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