Normal for SNR margin to gradually decrease?

My stats below show that Interleave is switched off and over a period of just over 10 days my CRC error rate is around 51 per hour which I believe is reasonably low for Fastpath (?).

I have noticed though with this and other "uptimes" that the SNR gradually goes down over the 10 days, eg its starts at 6.1dB and has now gardually gone down to 4.3dB. The fluctuation in the day is only around 0.2 dB.

Is this gradual reduction normal as it does not seem to be related to line noise in my opinion?



xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max: Upstream rate = 18312 Kbps, Downstream rate = 53568 Kbps
Path: 0, Upstream rate = 18715 Kbps, Downstream rate = 58253 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 4.3 5.7
Attn(dB): 0.0 0.0
Pwr(dBm): 13.1 6.8
VDSL2 framing
Path 0
B: 239 239
M: 1 1
T: 64 64
R: 0 14
S: 0.1311 0.4080
L: 14643 4980
D: 1 1
I: 240 127
N: 240 254
Counters
Path 0
OHF: 423205490 328556
OHFErr: 12709 422
RS: 0 1813621
RSCorr: 0 953
RSUnCorr: 0 0

Path 0
HEC: 33489 0
OCD: 0 0
LCD: 0 0
Total Cells: 1011506532 0
Data Cells: 3588224322 0
Drop Cells: 0
Bit Errors: 0 0

ES: 5534 378
SES: 4 0
UAS: 16 16
AS: 891336

Path 0
INP: 0.00 0.00
PER: 2.09 6.52
delay: 0.00 0.00
OR: 91.51 34.31

Bitswap: 158625 59099
#
#
#
#
#
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# xdslcmd info --stats
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max: Upstream rate = 18324 Kbps, Downstream rate = 53568 Kbps
Path: 0, Upstream rate = 18715 Kbps, Downstream rate = 58253 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 4.3 5.8
Attn(dB): 0.0 0.0
Pwr(dBm): 13.1 6.8
VDSL2 framing
Path 0
B: 239 239
M: 1 1
T: 64 64
R: 0 14
S: 0.1311 0.4080
L: 14643 4980
D: 1 1
I: 240 127
N: 240 254
Counters
Path 0
OHF: 423221633 333803
OHFErr: 12709 422
RS: 0 2149324
RSCorr: 0 953
RSUnCorr: 0 0

Path 0
HEC: 33489 0
OCD: 0 0
LCD: 0 0
Total Cells: 1015313267 0
Data Cells: 3589199356 0
Drop Cells: 0
Bit Errors: 0 0

ES: 5534 378
SES: 4 0
UAS: 16 16
AS: 891371

Path 0
INP: 0.00 0.00
PER: 2.09 6.52
delay: 0.00 0.00
OR: 91.51 34.31

Bitswap: 158637 59104

Total time = 1 days 7 hours 36 min 29 sec
FEC: 0 0
CRC: 12709 0
ES: 5534 378
SES: 4 0
UAS: 16 16
LOS: 0 0
LOF: 0 0
Latest 15 minutes time = 6 min 29 sec
FEC: 0 0
CRC: 4 0
ES: 3 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
Previous 15 minutes time = 15 min 0 sec
FEC: 0 0
CRC: 10 0
ES: 8 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
Latest 1 day time = 7 hours 36 min 29 sec
FEC: 0 0
CRC: 380 0
ES: 207 8
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
Previous 1 day time = 24 hours 0 sec
FEC: 0 0
CRC: 1412 0
ES: 579 33
SES: 1 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
Since Link time = 10 days 7 hours 36 min 11 sec
FEC: 0 953
CRC: 12709 422
ES: 5534 378
SES: 4 0
UAS: 0 0
LOS: 0 0
LOF: 0 0

Not normal.

I would expect there to be a fluctuation every day, starting to drip at sunset and getting to a minimum a couple of hours later then starting to rise just before sunrise to get back to the same level. Typically that will be around 3 dB but could be as low as 1dB or as high as 7dB. The same pattern would be there day after day.

Yes, I recognise the trend you describe from my ADSL connection days as the street lights come on at night etc. I am not seeing this though with my VDSL2 connection only the gradually reduction over quite a few days.

I have only seen a few VDSL traces, and then not very definitive but the characteristic still seemed to be there repeating over 24 hours without a day by day drop.

As for what is causing yours? Internal noise in the modem maybe?

We'd expect to see a reduction in SNR over time because other people are signing up to FTTC too. Each connection causes crosstalk on a neighbour (a neighbouring wire in the bundle, not necessarily a neighbouring property), and the amount of crosstalk depends on factors such as proximity within the bundle.

So the reduction in SNR (and/or an increase in errors) happens over time - but we can't say how long. It might be days, weeks or months... or it might happen from day 1. It depends mostly on when other people get connected.

Our connection degraded over 6 weeks from late November to early January, from around 7dB to around 5dB. We're still synchronised at 80Mbps, but we wouldn't get that if we resynch'ed now.

But from what teh OP says, 0.2dB per day ... too regular?

Just to clarify what I mean by 0.2dB, I'm referring to the fact that today for example, that sometimes I would see 4.5dB, others 4.3dB or 4.1dB.

That level of ripple through the day is quite normal.

So, did the large drop happen in one or several steps?

In reply to a post by MHC:

That level of ripple through the day is quite normal.

So, did the large drop happen in one or several steps?

several small steps over 10 days.