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Author Topic: Help with understanding SNR / Line Quality limitations  (Read 2290 times)

Skinnersplace

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Help with understanding SNR / Line Quality limitations
« on: October 10, 2021, 10:52:44 AM »

My first post in a while...

My HW set up, is a HG612 modem (running the SP08 firmware)  connected to a huawei cab approximate 1,877m from the exchange.
I have the QOS turned off on the modem as I have QOS enabled on ubiquity ER-X router which connects vis to NowTV's (sky's) service as ethernet over PTM over VDSL2

In august last year I changed from an ECI modem, so as to get the line stats more easily.

At that time my line stats were:

Max:    Upstream rate = 7969 Kbps, Downstream rate = 45012 Kbps
Bearer: 0, Upstream rate = 7969 Kbps, Downstream rate = 32399 Kbps
                Down            Up
SNR (dB):        10.4            6.2
Attn(dB):        21.6            0.0
Pwr(dBm):        11.8            3.5

GIMP is active.

This indicated an Openreach 40/10 Mbps banded to about 32Mbps at that time

I have since changed to a higher package and replaced my Mk1 filter faceplate with a Mk3, the stats are now as follows:

Stats recorded 10 Oct 2021 09:14:39

DSLAM type / SW version:   BDCM:0xa4a1 (164.161) / v0xa4a1
Modem/router firmware:     AnnexA version - A2pv6C038m.d24j
DSL mode:                  VDSL2 Profile 17a
Status:                    Showtime
Uptime:                    5 days 19 hours 24 min 18 sec
Resyncs:                   1 (since 03 Oct 2021 12:44:47)
         
            Downstream   Upstream
Line attenuation (dB):     21.5      0.0
Signal attenuation (dB):   Not monitored      
Connection speed (kbps):   58333      6660
SNR margin (dB):           3.1      6.1
Power (dBm):               12.8      -8.2
Interleave depth:          4      1
INP:                       52.00      0
G.INP:                     Enabled      Not enabled
Vectoring status:          5 (VECT_UNCONFIGURED)      

RSCorr/RS (%):             2.0502      0.6772
RSUnCorr/RS (%):           0.0000      0.0000
ES/hour:                   0.11      3.14


So I can see the banding has ben removed improving my download speed and the SNR(db's) and reduced to 3.1 down and 6.1 up

My upload speed is limited to 6Mbps,and I notice G.imp is not enabled on the upload path.
Is this simply down to my line quality / poor splices ?  i.e does the ES indicate that the line is particular noisy ?

« Last Edit: October 10, 2021, 11:55:24 AM by Skinnersplace »
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j0hn

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Re: Understanding SNR / Line Quality limitations
« Reply #1 on: October 10, 2021, 11:55:04 AM »

G.INP is disabled by default on the upstream on OpenReach VDSL2.

G.INP is only enabled on the upstream if the upstream breaches certain error thresholds. It is removed again as soon as the errors reduce back to an acceptable level.
There are very few lines that have upstream G.INP on all the time. They tend to be noisier lines.
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tubaman

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Re: Understanding SNR / Line Quality limitations
« Reply #2 on: October 10, 2021, 12:00:51 PM »

You might be 1.8km from the exchange but with those speeds I'd say you are way closer than that to your fibre cabinet.
G.INP is rarely active on the US side and even if it does turn on it won't drop you below 6dB anyway. I've seen it occasionally activate on my line following periods of bad noise but it rarely lasts more than a day or so before it gets switched off again.
Your US speed does look a bit low considering what you are getting on the DS side, but all lines are different in this respect so I'd say what you've got now is likely as good as it gets. The ES readings look pretty low to me.
 :)

Looks like @J0hn beat me to it!
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Skinnersplace

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Re: Help with understanding SNR / Line Quality limitations
« Reply #3 on: October 10, 2021, 12:03:47 PM »

Thanks John, that explains why the upstream G.IMP is disabled, can you see anything else indicating why the upload stream is impacted ?
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g3uiss

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Re: Help with understanding SNR / Line Quality limitations
« Reply #4 on: October 10, 2021, 01:10:46 PM »

With the US SNRM at 6.1 the line is flat out, I doubt you can improve in this.
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Skinnersplace

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Re: Help with understanding SNR / Line Quality limitations
« Reply #5 on: October 10, 2021, 01:24:11 PM »

Thanks Tubaman & G3uiss, that has confirmed what I suspected. the quality of the upstream pair seems to be limiting factor in my case.
You are correct Tubaman, closer to 180m from the cabinet
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tubaman

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Re: Help with understanding SNR / Line Quality limitations
« Reply #6 on: October 10, 2021, 01:59:46 PM »

Thanks Tubaman & G3uiss, that has confirmed what I suspected. the quality of the upstream pair seems to be limiting factor in my case.
You are correct Tubaman, closer to 180m from the cabinet

At that distance I'm surprised you can't get the full 80/20. Maybe it goes a rather circuitous route and/or there's aluminium cable thrown into the mix.
 :)
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Skinnersplace

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Re: Help with understanding SNR / Line Quality limitations
« Reply #7 on: October 10, 2021, 02:08:18 PM »

At that distance I'm surprised you can't get the full 80/20. Maybe it goes a rather circuitous route and/or there's aluminium cable thrown into the mix.
 :)

Yeah me to, however as I guess as there is no "Fault" as such, I would not be able to get BT out to check for any poor splices or to try the alternative pair
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tiffy

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Re: Help with understanding SNR / Line Quality limitations
« Reply #8 on: October 10, 2021, 02:46:56 PM »

You may be approx 180m from the fibre cabinet "as the crow flies" but who knows what route the copper (or ali.) cable takes, very hard to tell especially if underground distribution.

From your reported DS attenuation (21.6dB) and comparing this to my line and my daughters line which I monitor, I would think that your DS synch speed is likely as good as it gets for that line length, of course the "cross talk" factor on your line will be unique to you and will certainly be influential regarding the max. DS synch speed obtainable.
Looking as DS INP (52) I would guess that the line is on DS G.Inp re-tx high profile which will decrease the DLM BRAS IP profile and result in a lower data throughput speed for any given DS synch speed.

From my own experience, have found that US synch speeds attainable are more unpredictable and of course very much unique to each line.
For example, my line is comparable length to my daughters line but much better quality, minimal noise & error rates, however, I can only manage approx 5 Mbps US synch rate and she achieves close to 8 Mbps US synch.!
We are both on 40/10 service, different DSLAM's & ISDP's.
Despite her very poor quality, high noise line our DS synch speeds are very similar. 
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Skinnersplace

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Re: Help with understanding SNR / Line Quality limitations
« Reply #9 on: October 15, 2021, 09:45:02 AM »

You may be approx 180m from the fibre cabinet "as the crow flies" but who knows what route the copper (or ali.) cable takes, very hard to tell especially if underground distribution.

From your reported DS attenuation (21.6dB) and comparing this to my line and my daughters line which I monitor, I would think that your DS synch speed is likely as good as it gets for that line length, of course the "cross talk" factor on your line will be unique to you and will certainly be influential regarding the max. DS synch speed obtainable.
Looking as DS INP (52) I would guess that the line is on DS G.Inp re-tx high profile which will decrease the DLM BRAS IP profile and result in a lower data throughput speed for any given DS synch speed.

From my own experience, have found that US synch speeds attainable are more unpredictable and of course very much unique to each line.
For example, my line is comparable length to my daughters line but much better quality, minimal noise & error rates, however, I can only manage approx 5 Mbps US synch rate and she achieves close to 8 Mbps US synch.!

We are both on 40/10 service, different DSLAM's & ISDP's.
Despite her very poor quality, high noise line our DS synch speeds are very similar.

Thanks Tiffy, I also note the upstream bands U2,U3,U4 are missing in my pbParams output - is that also an indication that there is crosstalk on upload (that the DSLAM as opted not to use those frequencies ?)

xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason:   1
Last initialization procedure status:   0
Max:   Upstream rate = 6740 Kbps, Downstream rate = 59212 Kbps
Bearer:   0, Upstream rate = 6740 Kbps, Downstream rate = 59895 Kbps
Bearer:   1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Discovery Phase (Initial) Band Plan
US: (7,32) (871,1205) (1972,2782)
DS: (33,859) (1216,1961) (2793,3970)
Medley Phase (Final) Band Plan
US: (7,32) (871,1205)
DS: (33,859) (1216,1961) (2793,3970)
     VDSL Port Details        Upstream        Downstream
Attainable Net Data Rate:        6740 kbps          59212 kbps
Actual Aggregate Tx Power:      -   7.8 dBm           12.9 dBm
====================================================================================
  VDSL Band Status   U0   U1   U2   U3   U4   D1   D2   D3
  Line Attenuation(dB):   6.3   34.7   N/A   N/A   N/A   16.4   43.2   67.5
Signal Attenuation(dB):   6.3   33.4   N/A   N/A   N/A   24.3   42.8   68.1
        SNR Margin(dB):   6.1   6.3   N/A   N/A   N/A   3.2   3.1   3.0
         TX Power(dBm):   -18.6   -8.2   N/A   N/A   N/A   9.4   7.7   7.0
« Last Edit: October 15, 2021, 02:01:25 PM by Skinnersplace »
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g3uiss

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Re: Help with understanding SNR / Line Quality limitations
« Reply #10 on: October 15, 2021, 12:06:02 PM »

Yes that's correct and perhaps indicative that there is some AL cable in the route. It restricts the higher frequencies quite significantly
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Skinnersplace

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Re: Help with understanding SNR / Line Quality limitations
« Reply #11 on: October 15, 2021, 02:02:04 PM »

Yes that's correct and perhaps indicative that there is some AL cable in the route. It restricts the higher frequencies quite significantly

Thanks for the conformations g3uiss
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tubaman

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Re: Help with understanding SNR / Line Quality limitations
« Reply #12 on: October 15, 2021, 02:16:08 PM »

What's curious is that you have access to the D3 band which uses higher frequencies than U2, which is not working.
Band frequency details - https://kitz.co.uk/adsl/adsl_technology.htm
 ???
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Skinnersplace

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Re: Help with understanding SNR / Line Quality limitations
« Reply #13 on: October 15, 2021, 02:20:48 PM »

What's curious is that you have access to the D3 band which uses higher frequencies than U2, which is not working.
Band frequency details - https://kitz.co.uk/adsl/adsl_technology.htm
 ???

So maybe some specific interference in the    1972 -2782 tones (8.5 - 12 MHz)?
« Last Edit: October 17, 2021, 02:50:07 PM by Skinnersplace »
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j0hn

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Re: Help with understanding SNR / Line Quality limitations
« Reply #14 on: October 16, 2021, 11:58:41 AM »

My line made good use of the D3 band but didn't use a single tone on U2.

My FTTC was 55/9 before crosstalk knocked it down.
It went as low as 36/6 on a 6dB SNRM target and 44/6 on a 3dB target.
That was on brand new copper installed between cabinet and home to accommodate my new build development so no aluminium.

My U2 doesn't even show on an Hlog.
It happens on lots of longer lines. Might be related to UPBO? (upstream power back off).

If you use the BT Broadband Availability Checker does your sync rate fall within the VDSL2 estimates given for your address?
You may also find all your neighbours have similar low upstream estimates.
All my neighbours that share the same cabinet suffer similar low upstream estimates.
« Last Edit: October 16, 2021, 12:02:52 PM by j0hn »
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