SNR like a roller-coaster ? - help

[xlr8r]

hi guys.

 I wanted to know if anyone can advise on a solution for a problem i have with BT FTTC (Infinity 2 it was known as).

I use a Zyxel VMG8324-B10A router (in bridged mode) as a modem. and an Asus GT-AX11000 router.  Im on FTTC and Cabinet is a Huawei i believe, having looked it up.

Every day my line speed  will rise and fall for no apparent reason on the Zyxel (also happens with BT Openreach modem). Also, Each day my (DOWN ONLY) SNR will sits stable (at around 5.5) until around 7:30 am - 8:00 am when it jumps up to 9.2 ?? it does this every day, and reduces again around 9pm to normal.  it can drop as low as 2.2 (but briefly ? i.e. an hour or so) - (see screenshot)

What could cause such a sudden SNR increase and decrease ? And, what could be causing my dropouts ? (let me know if you need any additional data for diagnosis)

thanks

Occasionally i monitor line stats from my Zyxel modem, here is a days worth of SNR behaving badly!

Modem Stats

================================================================================
VDSL Training Status: Showtime
Mode: VDSL2 Annex B
VDSL Profile: Profile 17a
G.Vector: Enable
Traffic Type: PTM Mode
Link Uptime: 1 day: 12 hours: 40 minutes
===============================================================================
VDSL Port Details Upstream Downstream
Line Rate: 11.368 Mbps 59.806 Mbps
Actual Net Data Rate: 11.338 Mbps 59.807 Mbps
Trellis Coding: ON ON
SNR Margin: 6.1 dB 9.4 dB
Actual Delay: 0 ms 0 ms
Transmit Power: 6.6 dBm 13.9 dBm
Receive Power: 0.0 dBm -6.3 dBm
Actual INP: 0.0 symbols 55.0 symbols
Total Attenuation: 0.0 dB 20.7 dB
Attainable Net Data Rate: 11.338 Mbps 70.835 Mbps
===============================================================================
VDSL Band Status U0 U1 U2 U3 U4 D1 D2 D3
Line Attenuation(dB): N/A 29.9 48.6 N/A N/A 15.3 38.4 62.2
Signal Attenuation(dB): N/A 29.0 47.2 N/A N/A 18.0 38.0 62.4
SNR Margin(dB): N/A 6.1 6.1 N/A N/A 9.4 9.3 9.3
TX Power(dBm): N/A -13.0 6.6 N/A N/A 11.6 7.9 5.3
===============================================================================

VDSL Counters

Downstream Upstream
Since Link time = 40 min 15 sec
FEC: 158746699 198
CRC: 87 12
ES: 7 10
SES: 7 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 15 minutes time = 6 min 15 sec
FEC: 124777 0
CRC: 0 0
ES: 0 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: 183598 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 1 day time = 14 hours 21 min 15 sec
FEC: 101489128 85
CRC: 0 4
ES: 0 2
SES: 6 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Previous 1 day time = 24 hours 0 sec
FEC: 62710436 124
CRC: 3148 12
ES: 54 12
SES: 48 0
UAS: 1740 1693
LOS: 1 0
LOF: 3 0
LOM: 34 0
Total time = 1 days 14 hours 21 min 15 sec
FEC: 164199564 209
CRC: 3148 16
ES: 54 14
SES: 54 0
UAS: 1740 1693
LOS: 1 0
LOF: 3 0
LOM: 34 0
===============================================================================

[imjolly]

have you checked your landline for noise - dial 17070 option 2  should be silent and best with corded phone from test socket

[xlr8r]

Hi, i remember doing this test a year or so ago when it was just the same, there was no noise. i havent done the test recently , but i will later this evening when i get home. Remind me , is the noise test done with or without the Openreach Mk4 faceplate (ie or tested using the socket behind it) ?

thanks

[pippincp]

If done without the faceplate it doesn't rule out any internal wiring fault. Personally I'd do both.

[imjolly]

it is best to use the test socket behind the faceplate as this eliminates any problem with faceplate and internal wiring

[xlr8r]

ok, i rang home and asked the missus to do the noise test  (with faceplate attached) using an old wired phone. 

she says the line is crystal clear , no noise at all. (this was tested while the SNR value is at it peak, 9.3 SNR)

Oddly, when i looked at the stats after the noise test was done, the was a slight SNR increase (i.e. went up to 10 SNR) while it was being noise-tested ?

what's my next move ?

thanks

[xlr8r]

ok, no noise on line as per earlier post and graph (one little spike occurred on eth SNR while the noise test was being done).

what else can i do ?

[imjolly]

your connection speed will only change as and when there is a reset by modem dropping the internet connection.  your attainable speed will change with line conditions as your noise margin fluctuates so will your attainable speed but actual connection speed remains constant

[xlr8r]

OK GUYS , I have just had a bit of a eureka!! moment.... hopefully this will help others....

The one thing i never tested was our cordless house phone (duh!).

...and so what I did was , just for fun, to double micro-filter the phone-line socket (but leaving the VDSL socket untouched).

and guess what, immediately  the SNR dropped quite dramatically!!

SNR went from 9.3 down to 6.0 !! 

For double-micro-filtering, I tried 4 different micro-filters, each having mixed results. The best one turned out to be an 'unbranded' type with marked with only, ADSL SPLITTER - PBS-58043-C   

This was the one that worked in reducing SNR the most. And yes, the phone still works fine...

just need to see if i can tweak it a little more to find that 2.8 SNR sweetspot that I got for 2 hours....

SNR Graph after double-filtering with 4 different microfilters....

The phone base causing the problem!! (now heading for the recycle bin)...

Double microfiltered phone socket

Hope info helps. 

[pippincp]

I suspect it was more the faceplate not being seated correctly and changing filters has resolved it. Those faceplates are notorious for that.