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Author Topic: ADSL Line Outages - Equipment or Line  (Read 4853 times)

aesmith

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ADSL Line Outages - Equipment or Line
« on: December 20, 2018, 12:10:37 PM »

We've been getting some strange outages.   What seems to happen is the line suddenly goes down in terms of function, the ISP sees it as Down and no data is transferred.  PPP polling from the ISP is down.   Meanwhile both BT and my router see the DSL still in sync with SNR varying minute by minute as normal (ie not frozen at last remembered values).    In some episodes the router SNR has dropped down to near zero or even sub zero, this drop happening instantaneously but followed by small variations around that value for the remainder of the outage. 

On all occasions the line has immediately resumed normal service the moment a DSL retrain is triggered either by router command or by disconnecting cable (or power cycle).

Any ideas?   I was thinking equipment rather than line, because of the fact that it can always be cleared by a retrain, whereas if it was interference or other line issue then I wouldn't expect it to clear until the condition improved.

Same symptoms with my original Billion 7800DXL and with the new Zyxel 8924.

Thanks in advance, Tony S
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burakkucat

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Re: ADSL Line Outages - Equipment or Line
« Reply #1 on: December 20, 2018, 04:19:15 PM »

That is rather perplexing. I would agree with your suspicion; it does seem to be a CPE problem rather than a circuit (line) problem.

One other thought. Could there be a problem with the ISP/CP's equipment? Power-cycling or software forcing a re-train with the equipment at your end of the circuit also forces the ISP/CP's equipment to re-train the (line-card) port assigned to your circuit.
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #2 on: December 22, 2018, 09:36:53 AM »

I grabbed a couple of screenshots from an episode last night.  The line came back up immediately the router was reset.  Noise margin was bumping around as normal,  no CRCs being detected, then with no prior indication noise margin dropped to near zero with errors off the scale.   During this time BT status test showed line in sync, noise margin normal.  A&A saw it has hard down.

Yesterday 22:33:30    Yesterday 22:33:46    BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync BRAS=2676kb/s FTR=3200kb/s MSR=4000kb/s ServOpt=1 I/L=I A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE Up Sync=804kb/s LoopLoss=32.4dB SNR=6.1dB ErrSec=0 HECErr=0 Cells=3144 Down Sync=3044kb/s FTB LoopLoss=53dB SNR=5.9dB ErrSec=0 HECErr=N/A Cells=3532    auto-DOWN@a
 


Sync speed is low as well now, at all times.  Down from normal which should be around 4.2meg to now struggling to hit 3.7.

Edit - didn't realise the CRC graph hadn't attached
« Last Edit: December 22, 2018, 04:06:11 PM by aesmith »
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burakkucat

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Re: ADSL Line Outages - Equipment or Line
« Reply #3 on: December 22, 2018, 03:20:34 PM »

I am struggling to understand what could be the cause of your problem.  :-\
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #4 on: December 22, 2018, 04:09:07 PM »

Might be time to swap back to the Billion router, so I get a true before/after comparison.   It may be that the Zyxel is simply slower since I've never tried one when the line was good.
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Octal

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Re: ADSL Line Outages - Equipment or Line
« Reply #5 on: December 30, 2018, 06:55:07 PM »

What the heck is all that noise? It's been a few days since you posted, I'm just curious if things have settled down now after Christmas, I've got my suspicions what that might be.
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #6 on: December 31, 2018, 10:22:30 AM »

What the heck is all that noise?
I'm not convinced that the graphs actually mark an episode of noise, in particular because each episode is immediately cleared by a DSL re-sync.

Since my last post the behaviour has changed a couple of times.  A&A did "something" on 24th December, resetting some attributes to default before reporting the fault to BT.  In response the circuit started running at a sync speed of around 4.5meg at 6dB, which is super fast for us, but with zillions of errors.  After a couple disconnections it's changed to running just under 4meg (also at 6dB), but errors have cleared up.   I guess some sort of banding has been applied, as the attainable rate still shows as high, but the actual rate at the same SNR has reduced.   Or can different sorts of interleaving have that effect?  A&A have told me they can only set I/L On, Off or Auto, they can't control the actual level of interleaving.

If anyone can interpret, I've attached the connection states immediately after their change on the 24th, and from the same time of day yesterday.

Our BT "fault" got mis-routed by BT who were confused by lack of dial tone and passed it to the exchange who knocked it back as no fault found.  We're awaiting it getting re-activated.
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burakkucat

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Re: ADSL Line Outages - Equipment or Line
« Reply #7 on: December 31, 2018, 04:51:48 PM »

On performing a comparison of the "before" and "after" statistics for the circuit, there is one thing that is immediately obvious --

Mode:                   ADSL2+ Annex A   (before)
Mode:                   ADSL2 Annex A    (after)
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ejs

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Re: ADSL Line Outages - Equipment or Line
« Reply #8 on: December 31, 2018, 05:07:44 PM »

The 2018-12-30 stats have an unusually high INP level of 4.0, so that's probably on a banded profile, even if it's not at the top of the band. The banded profiles go with higher downstream INP levels than usual, I think there are even two different levels that can be selected for some of the banded profiles.
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #9 on: January 01, 2019, 10:27:56 AM »

On performing a comparison of the "before" and "after" statistics for the circuit, there is one thing that is immediately obvious --

Mode:                   ADSL2+ Annex A   (before)
Mode:                   ADSL2 Annex A    (after)

That's something odd about this Zyxel router.  It's configured to disable ADSL2+ so I would expect it to connect as ADSL2 at all times, however on some retrains it reverts and acts as if 2+ was enabled.  I haven't quite confirmed which sort of re-trains have that effect.
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #10 on: January 15, 2019, 04:25:47 PM »

The 2018-12-30 stats have an unusually high INP level of 4.0, so that's probably on a banded profile, even if it's not at the top of the band. The banded profiles go with higher downstream INP levels than usual, I think there are even two different levels that can be selected for some of the banded profiles.

From the BT diagnostic dumps on the portal ...

18th December, using A&A's chosen settings  ..
Product Info   WBC End User ACCESS
Profile Info   WBC 3M - 6M Medium delay (INP 2) 6dB Downstream, UC Medium delay (INP 2) 6dB Upstream (ADSL2+)
BRAS Profile   adsl3500


24th December after A&A reset to default ..
Product Info   WBC End User ACCESS
Profile Info   WBC 160K - 24M Medium delay (INP 1) 6dB Downstream, UC Medium delay (INP 2) 6dB Upstream (ADSL2+)
BRAS Profile   adsl3500

Today 15 Jan, this is the dog slow but zero errors configuration it's settled on ..
Product Info   WBC End User ACCESS
Profile Info   WBC 2M - 4M Medium delay (INP 4) 6dB Downstream, UC Medium delay (INP 2) 6dB Upstream (ADSL2+)
BRAS Profile   adsl3500


Currently back and forward between different parts of Openreach as usual.  Can't raise a Broadband fault as there's noise on the line, PSTN fault cleared because engineer thinks noise is not too bad, back to a BB fault, cleared again as all tests are OK, back again as a Lift and Shift - engineer's gone to the exchange tested and apparently decided it's not needed.   

While BT's been continuously saying there's no fault anywhere, the line dropped three time today with the same symptoms - A&A receive report that line has dropped, PPP fails, however line actually stays in sync and PPP stays down until a DSL retrain is triggered in some way.
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Weaver

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Re: ADSL Line Outages - Equipment or Line
« Reply #11 on: January 21, 2019, 07:10:16 AM »

Got anywhere since then? Any luck?  :(
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #12 on: January 21, 2019, 09:30:24 AM »

Not so far.   A&A are back on to BT confirming that the port reset has not cleared the fault as we had another outage on Saturday.  Not sure who's decision it is to carry out the Lift and Shift, whether BT declined to carry it out or maybe this instruction (request?) wasn't passed on to the actual engineer assigned.   The annoying thing is that he actually called me from the exchange and told me there was a fault with some equipment which had now been resolved.  In hindsight I should have asked outright "did you carry out a Lift and Shift?"

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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #13 on: February 01, 2019, 01:41:45 PM »

Fixed now I think, BT's notes from the last visit, although cryptic, confirm the L and S carried out.
 
21/01/2019 16:54 - Lift and shift completed as requested, customer advised
Did you renew any MDF jumpers ? - No
Was there an Openreach fault on the frame ? - No
Did you change the HDF tie pair ? - Yes - CP equipment fault
Did you have a co-op call with the CP ? - Yes
Did you complete the Frame Direct ? - Yes
Did you get dial tone on the MDF ? - Yes
Did you get DSL sync with an attenuator on the MDF ? - Yes
Did you prove connectivity from the MDF to HDF ? - Yes
Were the connections from the MDF to HDF the same as the Openreach records ? - Yes


Looking at our line since then we've not had another lockup, and attenuation has dropped by 1/2 dB which also supports the idea that something has actually been changed.   Not sure if it's related but our line seems to have settled into some sort of banded profile which nearly hits 4 meg while still running almost error free.  A&A have disabled DLM, meaning we should stay in that reasonably happy state indefinitely.
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aesmith

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Re: ADSL Line Outages - Equipment or Line
« Reply #14 on: February 08, 2019, 12:00:13 PM »

Fault is back after the Lift and Shift, with an outage just after I made my last post.    It was OK from the L&S for around two weeks, then one outage on the 1st Feb that I hoped was a one off.  Then another yesterday morning,  then another this morning from 01:28 until a manual retrain at 06:00.   And another starting at 06:52 which we are leaving down in the hope that BT will look at it in the failed state.

First response from BT ...
"KBD - Your fault has been diagnosed using the Knowledge Based Diagnostic Tool: NO BTW FAULT - No BTW network fault has been found on this circuit. Throughput tests show user is maximising upstream throughput which may be the cause of the Disconnection. Please resolve the issue with your customer directly."

I'd love to know why they think the upstream is being maxed out, given that PPP is down.
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