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Author Topic: Odd shaped SNR-vs-tone graph - line #4 fault again  (Read 8126 times)

Weaver

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Odd shaped SNR-vs-tone graph - line #4 fault again
« on: April 10, 2020, 02:01:00 PM »

This is the odd-shaped SNR-vs-tone graph that I get from my modem #4:



The others have the normal overall smooth curve apart from the usual notches at the top end, but anyway, without the depression at the very top seen here. Why do you think that depression might be there?



This is the graph for modem #3, for comparison purposes - the normal shape :





Here are the complete stats for modem #4:

xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:   8000
Last initialization procedure status:   0
Max:   Upstream rate = 442 Kbps, Downstream rate = 2940 Kbps
Bearer:   0, Upstream rate = 525 Kbps, Downstream rate = 2785 Kbps

Link Power State:   L0
Mode:         ADSL2 Annex A
TPS-TC:         ATM Mode(0x0)
Trellis:      U:ON /D:ON
Line Status:      No Defect
Training Status:   Showtime
      Down      Up
SNR (dB):    2.4       5.8
Attn(dB):    64.5       40.9
Pwr(dBm):    18.4       12.4

         ADSL2 framing
         Bearer 0
MSGc:      59      11
B:      28      62
M:      8      1
T:      3      1
R:      16      12
S:      2.6243      3.7736
L:      756      159
D:      1      8

         Counters
         Bearer 0
SF:      5746059      541776
SFErr:      994      5
RS:      140060197      3638675
RSCorr:      351555      22698
RSUnCorr:   1016      0

ReXmt:      448050      0
ReXmtCorr:   447986      0
ReXmtUnCorr:   1122      0

         Bearer 0
HEC:      1140      1
OCD:      2      0
LCD:      2      0
Total Cells:   606046574      114767360
Data Cells:   34016038      5929808
Drop Cells:   0
Bit Errors:   56760      1666

ES:      954      4
SES:      0      0
UAS:      53      53
AS:      92574

         Bearer 0
INP:      28.00      2.00
INPRein:   0.00      0.00
delay:      8      8
PER:      15.99      16.03
OR:      32.51      8.48
AgR:      2805.74   532.16

Bitswap:   21234/21234      105/105

Total time = 1 days 1 hours 43 min 47 sec
FEC:      351555      22698
CRC:      994      5
ES:      954      4
SES:      0      0
UAS:      53      53
LOS:      0      0
LOF:      0      0
LOM:      0      0
Latest 15 minutes time = 13 min 47 sec
FEC:      5613      188
CRC:      23      0
ES:      22      0
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Previous 15 minutes time = 15 min 0 sec
FEC:      6079      648
CRC:      20      0
ES:      20      0
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Latest 1 day time = 1 hours 43 min 47 sec
FEC:      37897      2090
CRC:      148      0
ES:      140      0
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Previous 1 day time = 24 hours 0 sec
FEC:      313658      20608
CRC:      846      5
ES:      814      4
SES:      0      0
UAS:      53      53
LOS:      0      0
LOF:      0      0
LOM:      0      0
Since Link time = 1 days 1 hours 42 min 53 sec
FEC:      351555      22698
CRC:      994      5
ES:      954      4
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
NTR: mipsCntAtNtr=0 ncoCntAtNtr=0




Summary of all modems - Live sync rates:
  #1: down 2898 kbps, up 529 kbps
  #2: down 2807 kbps, up 553 kbps
  #3: down 3066 kbps, up 396 kbps
  #4: down 2785 kbps, up 525 kbps
« Last Edit: April 10, 2020, 06:17:36 PM by Weaver »
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burakkucat

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Re: Odd shaped SNR-vs-tone graph
« Reply #1 on: April 10, 2020, 03:45:41 PM »

That's a strange looking plot. How does the equivalent Hlog (logarithmic representation of the channel characteristics function) plot look?  :-\
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Weaver

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Re: Odd shaped SNR-vs-tone graph
« Reply #2 on: April 10, 2020, 04:01:10 PM »

The hlog for modem #4 looks very unremarkable to me :

« Last Edit: April 10, 2020, 04:08:24 PM by Weaver »
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burakkucat

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Re: Odd shaped SNR-vs-tone graph
« Reply #3 on: April 10, 2020, 04:04:27 PM »

Hmm . . . Nothing odd there. I'm baffled.  ???
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Weaver

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Re: Odd shaped SNR-vs-tone graph
« Reply #4 on: April 10, 2020, 04:23:36 PM »

For some reason, the upstream was missing for modem #4 in the first shot, and now it has reappeared, so hereís modem #4 again:

« Last Edit: April 10, 2020, 04:26:28 PM by Weaver »
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Weaver

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Re: Odd shaped SNR-vs-tone graph
« Reply #5 on: April 10, 2020, 04:46:54 PM »

The line has gone bad again. It just didnít feel right, so I did a copper line test and the test failed, twice, with error message:

BT Test xDSL Copper Test:Inconclusive More diagnostics required Line test failure. Algorithm unable to continue.Inconclusive More diagnostics required Line test failure. Algorithm unable to continue. DS05:Test Failure - Please Retry - if unsuccessful report problem to OR via a Trouble Report

Third time lucky: the test completed with this fault message:

BT Test xDSL Copper Test:Pass Openreach network fault found.Pass Openreach network fault found. T023:FAULT - Battery Contact

So I reported this to AA, but they wonít be working today I presume. They do work on Saturdays though - they did submit a fault to OR for me on a Saturday before.
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burakkucat

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Re: Odd shaped SNR-vs-tone graph
« Reply #6 on: April 10, 2020, 05:03:37 PM »

I wonder if a joint closure has recently been opened, to fix a different fault in a cable pair, and the disturbance has impacted on your line #4 circuit.
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Weaver

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Re: Odd shaped SNR-vs-tone graph
« Reply #7 on: April 10, 2020, 06:16:21 PM »

Good point. Makes sense.

Itís a shame I donít have any data going back further. If OR did some work on something, as Burakkucat suggests, then we might see some change in a measurable stat at a certain time then.

I tested the other lines with the Ďcopper line testí and they look ok.



Question: on the CRCs vs time graph and FECs vs time graph what are the units on the axes ?

Recap: I apologise because I have asked this question before, Iím just rechecking my understanding and failing memory: Iirc, ĎFECsí is the count of errors detected and successfully fixed by using forward error correction maths, whereas ĎCRCsí is the number of errors detected but which could not be successfully corrected?
« Last Edit: April 10, 2020, 06:44:43 PM by Weaver »
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burakkucat

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Re: Odd shaped SNR-vs-tone graph
« Reply #8 on: April 10, 2020, 08:23:46 PM »

Question: on the CRCs vs time graph and FECs vs time graph what are the units on the axes ?

I shall have to let the maestro explain, as I do not use the firmware image.

Quote
Recap: I apologise because I have asked this question before, Iím just rechecking my understanding and failing memory: Iirc, ĎFECsí is the count of errors detected and successfully fixed by using forward error correction maths, whereas ĎCRCsí is the number of errors detected but which could not be successfully corrected?

Yes that's good enough explanation, for me.  :) 

I usually explain FECs (for those who are worring about the numbers noted) as "CRCs that did not occur due to the successful intervention of the (forward) error detection and correction mechanism".
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Weaver

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Re: Odd shaped SNR-vs-tone graph - line #4 fault again
« Reply #9 on: April 10, 2020, 08:30:58 PM »

Hereís a CRCs-vs-time graph for modem 4, to illustrate my question about axes and units :



Iím wondering what Δn is in Δn/Δt, the count per unit Ďwhat time intervalsí - the units up the y axis?
« Last Edit: April 10, 2020, 08:44:54 PM by Weaver »
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burakkucat

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Re: Odd shaped SNR-vs-tone graph - line #4 fault again
« Reply #10 on: April 10, 2020, 09:00:03 PM »

Ah, I see.

I believe that the y-axis is the number of CRCs per minute, while the x-axis is time.
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Weaver

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Re: Odd shaped SNR-vs-tone graph - line #4 fault again
« Reply #11 on: April 14, 2020, 12:43:44 AM »

What time interval, do you think, from a guess from the numbers?



Canít tell if OR has been out today (Monday) or not. Iím assuming not, as there are no relevant records in clueless.aa.net.uk. I canít see any engineerís notes. It was an English bank holiday for AA, although not for us up here.

The downstream sync has become very bad now, down to 2.5M Mbps d/s @ 3 dB SNRM. Thatís much worse than it has been; the only sign of any problem originally was that funny shaped noise graph and then the battery contact fail test result.

Waiting on faultbtconfirm   Wait customer confirms fault closed PSTN Fault - NSY   aa@a
11 Apr 10:12:11      Track PSTN Fault 5-7-201625816677 Notes Field: **Line Stability:**Network Stability:**Test Outcome:Fail**MFL:LN**Term Statement:LINE TERMINATION DETECTED**Line Signature:**Distance to Fault:0**Cable length:8.11**Test Start Time:2020-04-11T11:12:03**Test Stop Time:2020-04-11T11:12:03   bt
11 Apr 10:12:11      Track PSTN Fault 5-7-201625816677 Informational Message: 4465 Please refer to the Notes field for the actual message   bt
11 Apr 10:12:11      Track PSTN Fault 5-7-201625816677 Estimated Response Time: 2020-04-14T23:59:59   bt
11 Apr 10:12:11      Track PSTN Fault 5-7-201625816677 Status: Open - Associating Info   bt
11 Apr 10:11:25      Track PSTN Fault 5-7-201625816677 Informational Message: 4040 Notification only - Estimated Response Time.   bt
11 Apr 10:11:25      Track PSTN Fault 5-7-201625816677 Informational Message: 3100 Trouble Report Accepted   bt
11 Apr 10:11:25      Track PSTN Fault 5-7-201625816677 Estimated Response Time: 2020-04-14T23:59:59   bt
11 Apr 10:11:25      Track PSTN Fault 5-7-201625816677 Status: Open - New   bt
11 Apr 10:11:14      Track PSTN Fault 5-7-201625816677 Message Informational 9323 The asset care level 2.5 will be applied rather than the specified service level.


I notice it said ďEstimated Response Time: 2020-04-14T23:59:59Ē so they have all of Tuesday; perhaps that means an engineer might be sent out tomorrow. Perhaps they were all busy, but I would have thought it would have been Monday seeing as it isnít a Scottish bank holiday, and I have discovered faults at the weekend recently and had the engineer out on Monday.
« Last Edit: April 14, 2020, 01:08:19 AM by Weaver »
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burakkucat

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Re: Odd shaped SNR-vs-tone graph - line #4 fault again
« Reply #12 on: April 14, 2020, 01:20:50 AM »

What time interval, do you think, from a guess from the numbers?

I believe the data is harvested once a minute. So the quantity on the y-axis is the "number of events in the last minute" and the x-axis is every minute.
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Weaver

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Re: Odd shaped SNR-vs-tone graph - line #4 fault again
« Reply #13 on: April 14, 2020, 02:13:37 AM »

I got fed up with typing 192.168.n.1 all the time, so I defined some domain names m1.example.com, m2.example.com etc - something really short anyway - and it works very nicely because the browser remembers those domain names in its history and if you just type m4Ö say, it completes the rest.

For obvious reasons, in general youíre not supposed to define A or AAAA records with RFC1918 private target IP addresses, and I got a warning from AAís clueless.aa.net.uk serverís DNS record setup function and it coloured my new entry yellow, but it sensibly let me go ahead anyway.
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Weaver

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Re: Odd shaped SNR-vs-tone graph - line #4 fault again
« Reply #14 on: April 14, 2020, 11:57:22 AM »

Engineer has come out and just finished. I have the notes :

===Point Of Intervention notes===

Between this point...
- Location: In garden of clisham
- Work Point: JB26
And this point...

Plant details...
- Plant affected: JNT100
- Plant type: MC32

Multiple Intervention?: N
===Point Of Intervention notes ends===
(No manually entered closure notes)

=== QBC Summary Start ===

Customer Report: End customer advised the line was noisy.

Actions to resolve: Engineer has resolved the fault located at the D-side including aerial cables / lead-in / block terminal. There was a fault outside the end customer's curtilage caused by general wear and tear. The fault was fixed by clearing in joint.

Additional information: Engineer has not visited end customer premises.

Final alternate test results: Final FastTest performed from the customer premise.The test passed on 14/04/2020 11:33:48.
=== QBC Summary End ===
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