Line Speed keeps dropping

[#1]

Happy for a Plusnet Support agent to call me anytime.  

[#2]

@UKAussieP 

It's not SNR, it's SNR margin, and generally speaking its level controls your connection speed as a trade-off against stability.

If you want a higher SNR margin then you'll get a lower speed, but better stability.

Perhaps you'd like to research it for yourself as you seem to think higher is better;

SNR margin VDSL

[#3]

Hi @RobPN 

Thanks for your reply

If you look at my first post, I was getting consitent speeds of about 73Mbps (and I have been getting that for years), In March this dropped to about 64Mbps, and a couple of weeks ago, my speeds dropped again to 54Mbps - DLM reset and Im getting 56-57Mbps

I mention SNR Margins, because it seems to be 'artifically' increasing my speeds to 56Mbps, Id hate to see what my speeds where when it was normally at 6dB.  

So, the issue is.... Why has my speeds dropped.  What happened in March for it do so, and then again a couple of weeks ago.  To resolve an issue, one must investigate and determine the cause.

Cheers.

[#4]

@RobPN 

From your link:

Hence the reason I keep referring to it.

[#5]

Just phoned Plusnet Support. 

They will send me their own router - so they can do their tests.

[#6]

Plusnet - Are you still able to do the tests required if I put this new router into Modem/Bridge mode?

Cheers.

[#7]

The question not asked and investigated is why is the DS interleaved (and quite deeply) whereas the US is on fast path?

As for the AI reference to low SNRM being associated with connection instability, the point is being misconstrued and no context is being given.  There is nothing wrong with a 3dB MARGIN** is there is no environmental noise.

In an environment with RFI noise (REIN) in order to sustain a stable connection, it must have a MARGIN which is greater than the intermittent electrical noise.  In that context the AI summary is valid.

The presence of interleaving on the DS suggests that a high level of error management is being applied ... the question is why?  Typically the answer is found in the user's environment, not in the service provided.  Electrical equipment can (especially cheap PSUs) go marginal without actually failing.  It might be prudent to look into REIN.

@lahbrannan1  / @Windings  / @Marsh  - is there any suggestion in the BTOR history that there is elevated environmental noise or possibly cross talk, which might account for the interleaving being applied to maintain a stable, but slower, connection?

**MARGIN as reported by a router is not a fixed metric, but a point in time metric.

When a router re-syncs it does so at a speed which delivers the TARGET MARGIN over the then present background noise.  Consider the TARGET MARGIN being 6dB; at the time of a resync the connection speed (which remains the same for the duration of the xDSL session) will be negotiated to deliver a 6dB margin.  Thereafter...

• If there was noise present at the time of the resync and it abates, then the observed margin will rise
• If there was no noise present at the time of the resync and then it occurs, the observed margin will be observed to fall

Evaluating the observed margin in the absence of knowing the target margin (often recorded in the connection logs) does not necessarily deliver useful insight.

Without the means to dynamically monitor SNRM (see router stats below) one cannot be certain about a low observed value.  For the moment, I'd want to know why the DS is interleaved.

[#8]

Many thanks for the very detailed and thoughtful reply @Townman 

I also took note that the downstream is on Interleaved.  However, as far as I am aware, this has been like that for years.  So unfortunately, in my opinion this is not the change that caused my speeds to drop.  Nothing internally in my flat has changed in the last few months, no new electronic equipment, no new leads and certainly nothing changed in the area where the modem is located.

Other than a short blip a few years ago, where there was noise on the line - my down speeds have been maintained at around 70Mbps (there or there-abouts), and upload speeds about 18.5Mbps.

Equipment:

I am using a 0.5m RJ11 to RJ11 patch lead from the BT Socket, to a Draytek Vigor V167 (in modem mode).  I am also using a 5m CAT8 SFTP patch cable from the Draytek Modem to a Asus GT-BE98 router.

• Draytek Modem was purchased in March 2023
• Asus Router purchased in August 2024

Something happened in March 2025 to cause a 10Mbps speed drop, and then another 10Mbps speed drop about 2 weeks ago.  I feel that if the reason for this can be found, then a resolution can also be found

As I am using my own equipement, it seems PlusNet cannot accurately do their tests - Im expecting there Hub 2 router in the next day or two.  As currently I have a *very* many years old Plusnet router sitting in storage

I live in a large block of MDU flats, so whether there has been a change outside of my flat (within the flat complex itself, or from the flats to the cabinet) - or even the cabinet to the exchange.  Maybe someone has swapped a patch lead around somewhere that isnt shielded.  Who knows.

Until I put the Plusnet router on, Plusnet wont do a thing, and hopefully "my equipement" will be vindicated enough for a proper engineer to investigate.

But once again, many thanks for your detailed reply, it is appreciated.

[#9]

Plusnet router due today, but I am noticing that my line keeps disconnecting every couple of days, approx 1-2am time.  

[#10 · Accepted solution]

!! FIXED !!

Score -

Plusnet Hub 2 Router - 1

Draytek Vigor 167 - 0  (RIP Jan 2023 to Jun 2025)

• Recieved the Plusnet Hub Router and plugged it in, way and behold speeds went to 67-68Mbps (totally acceptable). 
• Changed the patch lead (RJ11-RJ11) that was in the box and put it on the Draytek modem, speeds went to 64Mbps (mmm, ok).  
• Reconnected original RJ11 patch lead on the Draytek modem, speeds stayed at 64Mbps.
• Reconnected Plusnet Hub 2 Router - Speeds instantly 67-68Mbps.
• Put Plusnet Hub 2 Router into Bridge mode.  Speeds still at 67-68Mbps.

Excellent.  

Unsure if DLM needs to be reset again due to me constantly turning off/on.

Many thanks to all that helped and advised

[#11]

With the Hub 2 in router mode, it would be good to see the line stats it reports and compare them to historic figures.

[#12]

Hi @Townman 

Can I assume from your reply that you cannot get the line stats in modem mode?  If thats the case, thats a real shame - as I can 'temporarily' put it back into router mode - however it would only be for a couple of hours.  It would be a headache to re-configure all network devices (and then to put it all back again).  Nevermind that I utilise a 10GbE port on my main router too.

I wonder if I can put it back to router mode in a couple of days, just to get those stats?

Cheers

[#13]

@UKAussieP 

If you connect a pc with a fixed IP address of say 192.168.1.200 mask 255.255.255.0 to one of the free LAN ports you will still have access to the  >Advanced settings >Technical log  >Information page.

Hope this helps