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Author Topic: SNR Margin going up and down constantly  (Read 6648 times)

bobmoss

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SNR Margin going up and down constantly
« on: August 20, 2018, 10:56:23 AM »

Hi, I've just had FTTC installed last week and today have installed DSLStats to look at my stats.

Looking at the SNR Margin graph, my Upstream is a steady flat line at 6.1db, however the downstream is all over the place. It has highs of 8.5 and lows of 4.8, it seems to be varying minute by minute.

I've attached a screenshot to show what I mean.

Is this normal? or does it indicate an issue?

I've got no phone extensions and if I unplug the phone it makes no difference at all. I've got a Mk4 VDSL faceplate installed.

Thanks.

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jelv

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Re: SNR Margin going up and down constantly
« Reply #1 on: August 20, 2018, 11:51:04 AM »

Is there background noise on the phone line when you use the quiet line test (dial 17070 option 2).
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bobmoss

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Re: SNR Margin going up and down constantly
« Reply #2 on: August 20, 2018, 12:07:10 PM »

Thanks for the reply. I've just plugged in a corded phone and tried that, no noise, clicks are anything.
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j0hn

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Re: SNR Margin going up and down constantly
« Reply #3 on: August 20, 2018, 02:23:53 PM »

Can you post your Hlog and QLN from DslStats.

The varying SNRM certainly isn't the norm but I've seen it on a number of lines.
It could be something simple like a neighbouring line with a faulty modem reconnecting to some other intermittent noise coming from who knows where what.
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bobmoss

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Re: SNR Margin going up and down constantly
« Reply #4 on: August 20, 2018, 04:20:17 PM »

Attached are my QLog and Hlog graphs. Thanks.
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bobmoss

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Re: SNR Margin going up and down constantly
« Reply #5 on: August 21, 2018, 03:27:33 PM »

I've had a look at the overnight graphs and the SNR margin goes all over the place overnight too, doesn't seem to be any difference depending on the time of day.

Thanks.
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kitz

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Re: SNR Margin going up and down constantly
« Reply #6 on: August 21, 2018, 07:46:30 PM »

The swing is more than 3dB so not normal.   :(
Upstream is rock steady.  If there was an impending fault such as a high open or bad wiring at the socket, then I'd expect to see something on the upstream too.

QLN shows some 'nice' regular bumps at 3150+ which usually indicates crosstalk, but I also note each curve starts with a spike.
Cant particularly spot anything obvious in hlog... its an even curve drop.   Bit of spikyness at tail end, but thats not unusual at the higher frequencies.

From the provided graphs I'm not sure what it could be other than some sort of REIN type noise.   
I'm presuming from the lack of comments from the other guys that they can't spot anything telling either :/
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burakkucat

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Re: SNR Margin going up and down constantly
« Reply #7 on: August 21, 2018, 07:51:24 PM »

I'm presuming from the lack of comments from the other guys that they can't spot anything telling either :/

I confess to scratching my head . . . and not coming up with any sensible conclusion.  :(
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d2d4j

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Re: SNR Margin going up and down constantly
« Reply #8 on: August 21, 2018, 09:30:21 PM »

Hi

It’s just a thought, sorry if I am wrong but does the line bypass any tress or overhanging branches

If it does, it could be rubbing

Many thanks

John
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burakkucat

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Re: SNR Margin going up and down constantly
« Reply #9 on: August 21, 2018, 09:39:49 PM »

Hmm . . . Then we would need to have a category of frequency division duplex (FDD) tree branches which only affect the DS and not the US.  :-\
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kitz

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Re: SNR Margin going up and down constantly
« Reply #10 on: August 21, 2018, 10:35:00 PM »

Good thought, but it is a bit odd that upstream is so steady. 

You could perhaps look at the bitload graphs to see if any tones may be struggling.   Also bitswaps per tone to see if there is a lot of bit swap at a particular frequency (both of these are under the 'Bits' tab).   Having looked at the QLN though unless it is intermittent noise bursts I suspect that may not tell us a lot either.
Its perhaps also worth looking at the SNRM per Band for the downstream to see if there is any of the subtone bands more affected than the others.

Without any further clues to go on, I would suspect that its most likely noise being injected into the line, but it is extremely difficult to say based on what graphs Ive seen so far.


Could I suppose be a line card flapping, but Openreach tend to pick these types of faults up themselves these days,  as it will usually affect a batch of users on the same DSLAM.
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d2d4j

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Re: SNR Margin going up and down constantly
« Reply #11 on: August 21, 2018, 11:20:58 PM »

Hi

Many thanks and sorry, I did say I could be wrong sorry

A couple of thoughts, which maybe dismissed as I’m sure they will be

Does the line run parallel to any mains cable

Is it possible to double filter the connection and then see the result

Many thanks

John
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bobmoss

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Re: SNR Margin going up and down constantly
« Reply #12 on: August 22, 2018, 09:17:40 AM »

Thanks evereyone for helping me out with this - it's much appreciated!

To answer a few questions and give a bit of an overview, I live in a small township on the Isle Of Skye and Fibre has only been available here for about a month. There are about 30 houses here and I am roughly 400 - 500m from the cabinet (my guess of line length). My phone cable runs underground all the way to the cabinet but some other properties have overhead cables.

When I first had Fibre installed last week I was using a Draytek 130 modem and didn't notice the SNR going up and down (does it report actual SNR?) but wasn't really looking for it. I installed a Zyxel VMG1312-B10D so that I could run DSLStats as my speed is around 40Mbs and the (low) estimate from my ISP was 60Mbs. Could it be a faulty modem?

I my house, the cable doesn't run parallel to any mains cables, but it could elsewhere.

I've included a few more graphs as requested from DSLStats.

Thanks.

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kitz

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Re: SNR Margin going up and down constantly
« Reply #13 on: August 22, 2018, 10:16:49 AM »

Quote
Draytek 130 modem and didn't notice the SNR going up and down

Without logging facilities it would be hard to spot.

Quote
my speed is around 40Mbs and the (low) estimate from my ISP was 60Mbs

So the line is actually syncing lower than the estimates?     It's possible that DLM has spotted the SNRM spiking which may have been causing errors... and thus taken action which would lower your sync speed.


If you can provide full stats, then we should be able to see if DLM has taken any action on your line.
This info can be obtained via the telnet command:  adsl info --stats or alternatively C&P everything under the 'Connection Stats' tab in DSL stats - Telnet Data.

If your actual sync speed is much lower than estimates then you should be able to get your ISP involved to ask for an engineers visit.   I notice that you are with one of the 'better' ISPs when it comes to fault reporting.     
What does BTw estimate your line capable of?  https://www.dslchecker.bt.com/





Quote
I live in a small township on the Isle Of Skye
One of our other regs lives on Skye, but not fortunate enough to have access to FTTC yet.
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bobmoss

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Re: SNR Margin going up and down constantly
« Reply #14 on: August 22, 2018, 10:55:53 AM »

I had some basic logging on the Draytek but it was only once every 10 minutes.

Attached is my dslchecker stats - To be honest I'm not sure they are correct, they are higher than I thought possible with my distance from the cab.

I think my next step will be to get Zen involved, but I wanted to rule out as many possibilities here as possible before contacting them.

One of our other regs lives on Skye, but not fortunate enough to have access to FTTC yet.

It's a bit of a lottery on Skye at the moment as to who gets it. We are lucky here as they laid fibre to a big mast to get highspeed internet to one of the islands and so put in a cabinet for us as part of that. People in the next township can't get it but they are pencilled in for FTTP!

Here are my C&P'd full stats:

xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    1
Last initialization procedure status:   0
Max:    Upstream rate = 9708 Kbps, Downstream rate = 47684 Kbps
Bearer: 0, Upstream rate = 9682 Kbps, Downstream rate = 45932 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State:       L0
Mode:                   VDSL2 Annex B
VDSL2 Profile:          Profile 17a
TPS-TC:                 PTM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        4.6             6.5
Attn(dB):        22.3            0.0
Pwr(dBm):        13.0            5.2

                        VDSL2 framing
                        Bearer 0
MSGc:           -6              26
B:              227             237
M:              1               1
T:              0               46
R:              10              16
S:              0.1579          0.7812
L:              12060           2601
D:              4               1
I:              238             127
N:              238             254
Q:              4               0
V:              0               0
RxQueue:                112             0
TxQueue:                28              0
G.INP Framing:          18              0
G.INP lookback:         28              0
RRC bits:               0               24
                        Bearer 1
MSGc:           90              -6
B:              0               0
M:              2               0
T:              2               0
R:              16              0
S:              10.6667         0.0000
L:              24              0
D:              1               0
I:              32              0
N:              32              0
Q:              0               0
V:              0               0
RxQueue:                0               0
TxQueue:                0               0
G.INP Framing:          0               0
G.INP lookback:         0               0
RRC bits:               0               0

                        Counters
                        Bearer 0
OHF:            0               471579
OHFErr:         44444           1
RS:             106855784               21683215
RSCorr:         3103460         4
RSUnCorr:       0               0
                        Bearer 1
OHF:            263657          0
OHFErr:         1234            0
RS:             1581572         0
RSCorr:         263634          0
RSUnCorr:       1216            0

                        Retransmit Counters
rtx_tx:         4694416         0
rtx_c:          1945820         0
rtx_uc:         3218062         0

                        G.INP Counters
LEFTRS:         4228            0
minEFTR:        43189           0
errFreeBits:    23348514                0

                        Bearer 0
HEC:            0               0
OCD:            0               0
LCD:            0               0
Total Cells:    274815489               0
Data Cells:     3540979         0
Drop Cells:     0
Bit Errors:     0               0

                        Bearer 1
HEC:            0               0
OCD:            0               0
LCD:            0               0
Total Cells:    0               0
Data Cells:     0               0
Drop Cells:     0
Bit Errors:     0               0

ES:             23034           3
SES:            8962            0
UAS:            100             89
AS:             4236

                        Bearer 0
INP:            52.00           0.00
INPRein:        1.00            0.00
delay:          0               0
PER:            0.00            9.01
OR:             0.01            28.38
AgR:            46033.29        9710.69

                        Bearer 1
INP:            2.50            0.00
INPRein:        2.50            0.00
delay:          0               0
PER:            16.06           0.01
OR:             47.81           0.01
AgR:            47.81   0.01

Bitswap:        3000/3025               13/13

Total time = 12 hours 57 sec
FEC:            79253419                11
CRC:            398463          3
ES:             23034           3
SES:            8962            0
UAS:            100             89
LOS:            1               0
LOF:            6               0
LOM:            580             0
Retr:           1
HostInitRetr:   0
FailedRetr:     0
Latest 15 minutes time = 57 sec
FEC:            35007           0
CRC:            506             0
ES:             28              0
SES:            11              0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            3               0
Retr:           0
HostInitRetr:   0
FailedRetr:     0
Previous 15 minutes time = 15 min 0 sec
FEC:            605760          3
CRC:            9408            0
ES:             484             0
SES:            183             0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            77              0
Retr:           N/A
HostInitRetr:   N/A
FailedRetr:     N/A
Latest 1 day time = 12 hours 57 sec
FEC:            79253419                11
CRC:            398463          3
ES:             23034           3
SES:            8962            0
UAS:            100             89
LOS:            1               0
LOF:            6               0
LOM:            580             0
Retr:           1
HostInitRetr:   0
FailedRetr:     0
Previous 1 day time = 0 sec
FEC:            0               0
CRC:            0               0
ES:             0               0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
HostInitRetr:   0
FailedRetr:     0
Since Link time = 1 hours 10 min 35 sec
FEC:            3103460         4
CRC:            44444           1
ES:             2493            1
SES:            952             0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            304             0
Retr:           0
HostInitRetr:   0
FailedRetr:     0
NTR: mipsCntAtNtr=0 ncoCntAtNtr=0
$
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