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Standard User madnutter56
(newbie) Mon 26-Nov-12 17:19:38
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Is this normal?


[link to this post]
 
Just posting this graph from my HG612 here for any opinions on whether this is a normal/expected level of crosstalk as a result of my neighbour having 80/20 FTTC installed this morning.

Graph Here

They have a 71.38Mbps IP Profile. We (currently) sync at the full 80/20, so 77.43Mbps profile. As you can see this won't be continuing due to our DS SNRM being ~ 4.5db, down from 8db this morning. I'm not too fussed just wondering if this is normal?

The increased crosstalk is causing some packet loss by the looks of my BQM.

I'm tempted to resync and take the hit on sync speed so the DLM doesn't step in and add interleaving.

Modem stats are: here and here.

Any thoughts?

Alex smile
Standard User Ixel
(member) Mon 26-Nov-12 18:36:13
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Re: Is this normal?


[re: madnutter56] [link to this post]
 
It looks a little odd in my view. Your line is closer than mine, lower line attenuation figures than my line, so I'm surprised your downstream speed is less than mine. Makes me wonder if there's a possibility of a line fault that's not clearly showing.

In my case, I had a lower speed a short while ago. I reported a fault to BT for another reason (one morning my whole internet was just getting bad throughput and ping, resolved itself in afternoon). Engineer arrived one morning (not planned) and still said there's a fault he needs to fix when I was sure it was resolved. Anyway, long story short he found a 'battery contact' fault of around 50v, he cleared most of it up and my attainable speed went up.

Here's my pbParams stats for comparison:
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# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 2Max:    Upstream rate = 28485 Kbps, Downstream rate = 93168 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 59999 Kbps 
Discovery Phase (Initial) Band PlanUS: (0,95) (880,1195) (1984,2771)
DS: (32,859) (1216,1959) (2792,4083)Medley Phase (Final) Band Plan
US: (0,95) (880,1195) (1984,2771)DS: (32,859) (1216,1959) (2792,4083)
       VDSL Port Details       Upstream        DownstreamAttainable Net Data Rate:      28485 kbps         93168 kbps
Actual Aggregate Tx Power:        6.8 dBm          12.5 dBm============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3  Line Attenuation(dB):  0.7     20.7    30.6     N/A    11.3    26.5    40.8
Signal Attenuation(dB):  0.7     20.6    30.5     N/A    11.3    26.5    40.8        SNR Margin(dB):  12.6    12.4    11.9     N/A    14.9    15.3    14.8
         TX Power(dBm): -4.1    -23.1    6.4      N/A    8.9     7.7     6.4


That comes from the current_stats output by the graphing scripts.
Standard User MHC
(sensei) Mon 26-Nov-12 20:23:30
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Re: Is this normal?


[re: madnutter56] [link to this post]
 
4.5 dB at this time of day will increase again tomorrow morning.

With an 8dB margin and full sync you have some in hand so you may/maynot see a slight drop.

Cross talk from a neighbour will cause increased noise especially if they share a drop wire or the final cable with you.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit


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Standard User madnutter56
(newbie) Mon 26-Nov-12 20:39:34
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Re: Is this normal?


[re: Ixel] [link to this post]
 
In reply to a post by Ixel:
It looks a little odd in my view. Your line is closer than mine, lower line attenuation figures than my line, so I'm surprised your downstream speed is less than mine. Makes me wonder if there's a possibility of a line fault that's not clearly showing.


Hmm, do you have any idea how many FTTC lines there are on your cab? I know there are at least 10 on our road (almost half the street), so I'd imagine there's quite a bit of crosstalk already dragging it down.

There may well be some kind of fault here but the problem is getting anyone to care about it, given that I'm still syncing at 79999 or ~75000 if/when I reboot.

Alex smile
Standard User madnutter56
(newbie) Mon 26-Nov-12 20:42:18
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Re: Is this normal?


[re: MHC] [link to this post]
 
I don't think I explained it too well, basically up until this morning, I had an 8db margin with full 79,999 sync.

I still have 79,999 sync but the margin is down at 4.5db because of the increased crosstalk from the neighbours install, I was wondering if this is excessive?

Strangely our DS SNRM only seems to drop by 0.1 or 0.2db at night so that isn't affecting it much if at all.

Given that they are our neighbour, I'd take a guess they are on the same (underground) DP and thus the same cable back to the cab as us?

Edited by madnutter56 (Mon 26-Nov-12 20:43:01)

Standard User MHC
(sensei) Mon 26-Nov-12 21:17:57
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Re: Is this normal?


[re: madnutter56] [link to this post]
 
So just a small day night change.

It is high but not excessive. The feed from the cabinet to the pole could be a 10 pair, 25 or 100 ... and if your pair is close to another that is carrying VDSL signals then there will be a lot of cross talk. If you are on the opposite side of the bundle then it may be you would see no change. Predicting the effects of cross talk is a very difficult art and never perfect.

There are lots of reasons as to why the effect is so high and they would all be guesses and could send you on a wild goose chase ... For example and it is just an example so don't go looking! Your neighbour could have a phone cable that is a perfect antenna for a radio station ... so it picks up the transmission and that affects his signal ... because it is injected into his wiring, you will get a cross talk effect from that and it will hit your sync too.

Do a modem reset - just one and see where it comes back. Gut feel says you will only be just under full sync and not as low as your neighbour.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User WWWombat
(experienced) Mon 26-Nov-12 21:21:32
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Re: Is this normal?


[re: madnutter56] [link to this post]
 
I might not go to say that your case is "normal", it is certainly the kind of effect that could be expected. Your neighbour's line is one of the ones most likely to cause crosstalk with yours, but not guaranteed. The lines need to be running close together within the outer sheath; the closer they are, the more crosstalk... and it isn't just the drop line that matters, it is the whole of the distribution cable on the way back.

It could just as easily have been someone in the next street.

Your error rate looks perfectly fine - the modem stats show increased FEC counts (so the errors are getting corrected) and zero in the CRC counts. The small blobs on the BQM aren't enough to worry about.

It does, however seem likely that you'll still lose some of your speed if you resync

Before you do, can you post the output from the "xdslcmd info --stats" command? It'd be good to see the setup of your interleaving & FEC configuration.
Standard User RobertoS
(sensei) Mon 26-Nov-12 21:24:57
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Re: Is this normal?


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
Before you do, can you post the output from the "xdslcmd info --stats" command? It'd be good to see the setup of your interleaving & FEC configuration.
xdslcmd info --pbParams can be very useful as well. It shows what is in use out of what was "discovered".

My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet Extra Fibre (FTTC). Sync ~ 53.5/15.2Mbps @ 600m. - BQM

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
Standard User madnutter56
(newbie) Mon 26-Nov-12 21:34:22
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Re: Is this normal?


[re: WWWombat] [link to this post]
 
OK so here's the data requested from the modem:

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# xdslcmd info --stats
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 1Max:    Upstream rate = 27099 Kbps, Downstream rate = 74428 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 79999 Kbps 
Link Power State:       L0Mode:                   VDSL2 Annex B
VDSL2 Profile:          Profile 17aTPS-TC:                 PTM Mode
Trellis:                U:ON /D:ONLine Status:            No Defect
Training Status:        Showtime                Down            Up
SNR (dB):        4.5             12.2Attn(dB):        0.0             0.0
Pwr(dBm):        13.9            6.0                        VDSL2 framing
                        Path 0B:              239             237
M:              1               1T:              23              45
R:              0               16S:              0.0955          0.3782
L:              20107           5373D:              1               1
I:              240             127N:              240             254
                        Counters                        Path 0
OHF:            28926201                3357163OHFErr:         3805            63
RS:             0               3396968RSCorr:         0               264
RSUnCorr:       0               0 
                        Path 0HEC:            4283            0
OCD:            0               0LCD:            0               0
Total Cells:    3060538644              0Data Cells:     29094453                0
Drop Cells:     0Bit Errors:     0               0
 ES:             5072            113
SES:            13              4UAS:            59              59
AS:             47835 
                        Path 0INP:            0.00            0.00
PER:            1.64            4.25delay:          0.00            0.00
OR:             116.56          60.17 
Bitswap:        10247           656 
Total time = 1 days 4 hours 57 min 36 secFEC:            0               0
CRC:            15501           0ES:             5072            113
SES:            13              4UAS:            59              59
LOS:            10              0LOF:            5               0
Latest 15 minutes time = 12 min 36 secFEC:            0               0
CRC:            135             0ES:             123             0
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0
Previous 15 minutes time = 15 min 0 secFEC:            0               0
CRC:            204             0ES:             178             0
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0
Latest 1 day time = 4 hours 57 min 36 secFEC:            0               0
CRC:            2352            0ES:             1711            17
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0
Previous 1 day time = 24 hours 0 secFEC:            0               0
CRC:            8399            0ES:             1406            30
SES:            11              0UAS:            40              40
LOS:            10              0LOF:            5               0
Since Link time = 13 hours 17 min 15 secFEC:            0               264
CRC:            3805            63ES:             2688            36
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0


and
Text
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xdslcmd: ADSL driver and PHY status
Status: ShowtimeRetrain Reason: 1
Max:    Upstream rate = 27115 Kbps, Downstream rate = 74428 KbpsPath:   0, Upstream rate = 20000 Kbps, Downstream rate = 79999 Kbps
 Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783)DS: (32,859) (1216,1963) (2792,3959)
Medley Phase (Final) Band PlanUS: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:      27115 kbps         74428 kbpsActual Aggregate Tx Power:        6.0 dBm          13.9 dBm
============================================================================  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB):  2.9     16.9    24.7     N/A    9.7     21.2    31.8 
Signal Attenuation(dB):  2.9     15.8    24.1     N/A    9.7     21.2    31.8 
        SNR Margin(dB):  12.1    12.2    12.2     N/A    4.4     4.5     4.5 
         TX Power(dBm): -9.2    -28.7    6.0      N/A    11.2    8.0     6.9


I will do a resync in the morning and see what happens then smile
Standard User Ixel
(member) Mon 26-Nov-12 22:07:10
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Re: Is this normal?


[re: madnutter56] [link to this post]
 
I'd imagine at least a dozen or more, Openreach have been at the cabinet on a regular basis over the past few months since FTTC was available here. I was first for FTTC in the cabinet and am getting about 12 megabits (downstream) less than I did when I was first activated. Sadly I don't know where the stats are for back then (I think I had them on my SSD which I had to send back ages ago as it just failed suddenly).
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