BT 80/20 - 20% reduction in DS sync after several years

I have been with BT for several years and am currently on their Halo 1 FTTC product. In October 2017, for no extra charge BT migrated me onto the 80/20 product so I had the maximum speeds possible.

I have therefore enjoyed a sync rate of 79XXX/ 19XXX up for many years (I forget exactly because frustratingly I don't have a copy of my previous router stats) and generally an excellent experience with months of uptime.

Link to BT Home Hub overview (alas not stats) following switch to 80/20 product.


My setup is a Huawei HG612 modem connected to a Ubiquiti Unifi Security Gateway (USG) which acts as gateway, router, firewall, DHCP server etc.. Therefore, the sync is all on the HG612 modem.

The power supply on the USG failed (27 November). I was not at home at the time so the internet remained down for 10 days. I have returned home, and before turning off the HG612 I noted from the lan interface that the sync speed had dropped. I paid little attention thinking it was to do with whatever problem had taken down the connection and temporarily connected the BT Home Hub 5 (Correction: Home Hub 6A) to confirm the line was good, and then replaced the power supply on the USG so it is now working again.

The HG612 is now consistently syncing at a far lower rate downstream of around 67,600kbps. The upstream remains unaffected. The downstream SNR margin is 6.3dB and I'm frankly lost as to what has led to this considerable change.

Full stats below:

Stats recorded 08 Dec 2021 17:02:54

DSLAM type / SW version: BDCM:0xa4a1 (164.161) / v0xa4a1
Modem/router firmware: Not monitored
DSL mode: VDSL2 Profile 17a
Status: Showtime
Uptime: 16 hours 17 min 31 sec
Resyncs: 3 (since 06 Nov 2021 12:15:21)

Downstream Upstream
Line attenuation (dB): 14.9 0.0
Signal attenuation (dB): Not monitored
Connection speed (kbps): 67652 19999
SNR margin (dB): 6.3 15.2
Power (dBm): 13.4 6.6
Interleave depth: 8 1
INP: 48.00 0
G.INP: Enabled Not enabled
Vectoring status: 5 (VECT_UNCONFIGURED)

RSCorr/RS (%): 0.0000 0.0072
RSUnCorr/RS (%): 0.0000 0.0000
ES/hour: 0 13.5

Can anyone shed any light on this?

I have also linked the Bitloading output from DSL stats, in case this means more to those more technical than me!

Please let me know if any more information will help and I will do my best to help. A 20% reduction isn't the end of the world but it is frustrating given it's on an otherwise reliable line. It even had me looking again at Virgin Media's offerings after swearing off them for many years!

Edit to correct signature:
-----------------------------------
BT Broadband Halo 1 FTTC 80/20
79,XXX/19,999 sync
Modem: Huawei HG612 3B modem
Router: Ubiquiti Unifi Security Gateway

Old signature:

Edited by oracleredux (Wed 08-Dec-21 19:31:45)

Brief improvement in SNR for a short period this afternoon:
Graph
Which makes me wonder if there is interference somewhere.

Is it similar with the HH5?

In reply to a post by witchunt:

Is it similar with the HH5?

I should correct myself - it's the Home Hub 6A, and nope, it is not:

Main connection page

Technical stats

A further update - according to the HG612 web interface, the SNR margin on the downstream is actually 14.9dB.

Screenshot

This is confusing since the SNR from dslstats (which uses Telnet) remains around 6dB:

Stats summary
Stats recorded 09 Dec 2021 09:04:54

DSLAM type / SW version: BDCM:0xa4a1 (164.161) / v0xa4a1
Modem/router firmware: Not monitored
DSL mode: VDSL2 Profile 17a
Status: Showtime
Uptime: 13 hours 49 min 12 sec
Resyncs: 4 (since 06 Nov 2021 12:15:21)

Downstream Upstream
Line attenuation (dB): 14.9 0.0
Signal attenuation (dB): Not monitored
Connection speed (kbps): 67422 19999
SNR margin (dB): 6.4 15.3
Power (dBm): 13.4 6.6
Interleave depth: 8 1
INP: 48.00 0
G.INP: Enabled Not enabled
Vectoring status: 5 (VECT_UNCONFIGURED)

It looks like the command line is showing the 14.9dB figure as line attenuation vs the web interface which shows it as SNR margin.

Does anyone known whether the SNR margin pulled from command line or that on the web interface is correct?

If the downstream SNR is indeed 14.9dB then I do I need to contact BT or wait for the DSLAM to force a resync after the line has been stable for a while?

IIRC from over a decade ago, the web interface on the HG 612 always had that problem. Note that the attenuation and power lines have identical values. (The units of course being different in the label).

Telnet will be showing the correct figure.

Thanks @pluralist.

I figured as much given the Telnet and BT HH6 figures were more aligned.

Alas that does not answer my question as to why there has been such a reduction in line sync speed.

Bitloading

The bitloading output looks odd to me given the trough between Tone numbers 150 and 300 but I am not clear what it should look like.

Edited by oracleredux (Thu 09-Dec-21 09:52:23)

Can you get an image of ALL tones - right uop to 4000+

In reply to a post by MHC:

Can you get an image of ALL tones - right uop to 4000+

Thanks for the response - please see screenshot below:
Bitloading - all tones

Hope that was what you were after?

The oddity I notice there is that the tones finish rather earlier than I would expect - 4096 is, I belive, the top. Nothing looks totally untoward - just maybe a little low - I might have expected some in D1 to be up in the 14/15 bits and more at 12.