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Author Topic: Zero crosstalk comparison ?  (Read 1841 times)

Weaver

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Zero crosstalk comparison ?
« on: August 14, 2016, 07:30:27 PM »

Background: There has been a massive local power cut, still in progress. I'm writing this while on my generator. I was asleep when my useless UPSs failed, ran out of energy and the wireless LAN went off while I was still asleep. When I woke up, the generator was turned on and the modems reconnected.

All the three modems have a substantially higher downstream sync rate now they're powered back up, around 200 kbps higher. And Andrews and Arnold's clueless.aa.net.uk server reports BRAS true delivery rates that have immediately gone up (no delay, like in the old days on 20CN where the rate increase notification would always be really late).

A speed test from speedof.me reports 7.4 Mbps combined downstream throughout, which is around ~1 Mbps higher than it has been of late. (The thinkbroadband speed checker reports no change and a much lower figure, so maybe the path to that server is a bit rubbish?)

I'll post the details of the modem info shortly when I feel a bit less groggy.

The point is, is this suddenly an experiment into the effect of the removal of all crosstalk. Presumably all the rest of my neighbours at the end of our five mile long copper bundle have their DSL modems off now, as I don't believe anyone else has a generator. So, apart from any possible locals very near the exchange who are in Broadford itself who have generators, this ought to be a measure of the situation with ADSL2 with all crosstalk removed.
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ejs

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Re: Zero crosstalk comparison ?
« Reply #1 on: August 14, 2016, 07:44:08 PM »

How do you know it's all due to the removal of crosstalk, and not partly due to the removal of RFI from all sorts of electrical devices that have also been switched off by the power cut?
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S.Stephenson

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Re: Zero crosstalk comparison ?
« Reply #2 on: August 14, 2016, 07:45:57 PM »

Here's an example on my VDSL connection during a power cut, I've been considering taking out the national grid ever since and living off a generator.

The line only cut out cause I tried to catch a higher sync by rebooting my modem.
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Weaver

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Re: Zero crosstalk comparison ?
« Reply #3 on: August 14, 2016, 08:14:11 PM »

ejs makes a very good point, which I hadn't thought of, but which I take on board.

I could indeed normally be suffering from EFI caused by noise generators near the line in Broadford, but those noise inputs would be attenuated by four miles of copper (66dB). As for local noise sources, I don't have any really close neighbours, the nearest dwelling is say 300m away and not near the line. My own house is extremely RFI-clean, I believe, by design. The drop wire doesn't run inside the house or round the outside wall at all. The mains to the modems is triple filtered using a variety of different devices.

Things like radio stations will not have changed, they won't have lost their power as they're not close enough to be in the affected area. (The 3G didn't go off, for the first time ever, meaning that at least my wife was able to notify the power company.)

So because of my highly unusual geography, my best guess is that there hasn't been a change in the levels of RFI. There isn't any kind in human or technological site anywhere near the line for something like four miles once it leaves the noisy environment if Broadford.

So I certainly can't _prove_ the crosstalk-only theory. But I think in this particular case it's a good bet.

« Last Edit: August 14, 2016, 08:17:09 PM by Weaver »
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ejs

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Re: Zero crosstalk comparison ?
« Reply #4 on: August 14, 2016, 08:29:17 PM »

The noise inputs "near the line in Broadford" being "attenuated by four miles of copper (66dB)" doesn't really make sense. If they are near the line, then they are near the line, and the noise would be induced into the line at that point. The downstream signal at any particular point in the cable would be strongest near the exchange, although your upstream signal in the cable, at that point, would be attenuated by four miles of copper.

Right now I've got a barely working broadband connection, there's so much noise detectable with an AM radio near the line that I could probably trace its exact route back to the cabinet! I get the impression that once at load of noise gets into the line somewhere, it gets carried along the line quite well.

Crosstalk is essentially just noise, induced into the line from other lines. Aren't there relatively few other lines running along your line for most of the way? So presumably most of the crosstalk would also be in Broadford near the exchange where lots of other lines are.
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Weaver

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Re: Zero crosstalk comparison ?
« Reply #5 on: August 14, 2016, 08:34:50 PM »

Btw my wife said 800 households were affected, so it is presumably confined to the Broadford area. The power is back on again now. About to capture more basic modem stats.
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Weaver

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Re: Zero crosstalk comparison ?
« Reply #6 on: August 14, 2016, 10:05:20 PM »

Modem status data, pre-, during, and post-outage. Times three lines.



-- line 1: --

post power outage:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2232kb/s FTR=1817kb/s MSR=2272kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=519kb/s LoopLoss=42.7dB SNR=6.1dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2592kb/s LoopLoss=65.2dB SNR=1.6dB ErrSec=1 HECErr=N/A Cells=0
cwcc@a

Today 19:48:38 Tx rate (adjusted) 2406978 to 2279088

Today 18:52:21 During power cut:
BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2232kb/s FTR=1817kb/s MSR=2272kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=525kb/s LoopLoss=42.7dB SNR=5.9dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2738kb/s LoopLoss=66dB SNR=3dB ErrSec=0 HECErr=N/A Cells=0
cwcc@a

Today 18:38:42 Tx rate (adjusted) 2225286 to 2406978

Today 00:44:04 Pre power cut
BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2232kb/s FTR=1817kb/s MSR=2272kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=515kb/s LoopLoss=42.9dB SNR=6.4dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2531kb/s LoopLoss=66.2dB SNR=1.4dB ErrSec=0 HECErr=N/A Cells=0

===

-- line 3 --

Post power outage:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2306kb/s FTR=1817kb/s MSR=2272kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=402kb/s LoopLoss=43.1dB SNR=6.3dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2624kb/s LoopLoss=65.7dB SNR=2.8dB ErrSec=0 HECErr=N/A Cells=0
cwcc@a

Today 19:48:38 Tx rate (adjusted) 2391102 to 2307312

Today 18:52:41 During power cut:
BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2306kb/s FTR=1817kb/s MSR=2272kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=402kb/s LoopLoss=43.1dB SNR=6dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2720kb/s LoopLoss=66.5dB SNR=3dB ErrSec=0 HECErr=N/A Cells=0
cwcc@a

Today 18:38:43 Tx rate (adjusted) 2298492 to 2391102 Friday 00:23:22

Tx rate (adjusted) 2216466 to 2298492

10 Aug 20:58:57 Pre power cut:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2223kb/s FTR=1817kb/s MSR=2272kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=402kb/s LoopLoss=43.1dB SNR=6.1dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2521kb/s LoopLoss=66.3dB SNR=2dB ErrSec=0 HECErr=N/A Cells=0

===

-- line 4 --

Post power outage:
Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2364kb/s FTR=2278kb/s MSR=2848kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=406kb/s LoopLoss=43.3dB SNR=5.9dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2691kb/s LoopLoss=66.4dB SNR=2.9dB ErrSec=0 HECErr=N/A Cells=0
cwcc@a

Today 19:48:38 Tx rate (adjusted) 2406978 to 2365524

Today 18:52:58 During power cut:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2364kb/s FTR=2278kb/s MSR=2848kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=406kb/s LoopLoss=43.3dB SNR=6dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2738kb/s LoopLoss=66.4dB SNR=2.9dB ErrSec=0 HECErr=N/A Cells=0
cwcc@a

Today 18:38:43 Tx rate (adjusted) 2356704 to 2406978

10 Aug 21:00:31 Pre power cut:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2364kb/s FTR=2278kb/s MSR=2848kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=409kb/s LoopLoss=43.5dB SNR=5.9dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2681kb/s LoopLoss=66.6dB SNR=1.7dB ErrSec=0 HECErr=N/A Cells=0
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