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Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

Posts: 25
Registered: ‎26-02-2019

Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

This is the kind of noise margin I used to have prior to 1st of October before EO Line was connected to Cabinet 20. 

7 - Data rate: 623/14326
8 - Maximum data rate: 1084/18228
9 - Noise margin: 14.5/11.2
10 - Line attenuation: 13.3/25.0

At 14326 Kbps which in real terms is more like 12.30 Mbps in speed test I was achieving 9-11 dB noise margins and my connection used to be more stable.

In fact it was stable for 34 days at a time. But after over 10 years of waiting to be upgraded to Fibre to the Cabinet as I was on an Exchange Only Line. On the 1st of October this year my area finally got upgraded to a new fibre cabinet. FTTC is finally available to order.

However, this has resulted in deteriorated noise margins on ADSL. I am no longer able to sync at 14000+ Kbps data rate at 9dB noise margins. Now my noise margins are down to 7.3 dB. This is not a coincidence, sadly!

6 - Uptime: 1 days 02:43:28
7 - Data rate: 1228/14335
8 - Maximum data rate: 1228/16900
9 - Noise margin: 6.0/7.3
10 - Line attenuation: 13.3/25.5

Now obviously I don't know what the service is like on FTTC. I'm assuming that the Cabinet 20 being located in Frostic Walk the length of copper wire will be shorter. But BT Openreach appeared to have extended the length of the copper cable during the re-arrangement of the line to the new cabinet.

This means the length has been extended and the copper cable on ADSL is picking up more noise which is contributing to now only 7.3 dB at 14335 Data rate instead of 9dB. This is certainly a damaged performance as following a drop-out few weeks ago I was syncing at 11440 Kbps at below 10Mbps at 12dB something that has never been the case before. Although the connection uptime this time was 23 days, there was an electric outage yesterday and while the the speed went back to 12+ Mbps the noise margins still remained suppressed at 7.3 dB.

Now I know my connection will no longer be stable at 12 Mbps ever again because of this new cabinet. Anyway. what are the chances that FTTC will solve this? I need to wait of-course till January for the current ADSL contract to end to switch to Fibre. The cabinet is around 320 meters to my home. But certainly this new change from BT Openreach seemed to have deteriorated ADSL performance.

Plusnet Alumni (retired)
Plusnet Alumni (retired)
Posts: 1,915
Fixes: 75
Registered: ‎11-01-2018

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!


Hi @serajmi


I'm unsure what impact upgrading to fibre would have on your noise margins - they are certainly less relevant on a fibre connection (due to the differing method of connectivity and the higher speeds this entails). One thing that I would point out though is that you DON'T need to wait for your current ADSL contract to end to upgrade to fibre - you can upgrade to fibre from ADSL at any time via my colleagues in the Customer Options Team on 0800 328 4624


Best wishes



Posts: 25
Registered: ‎26-02-2019

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

Well there would still be an impact as FTTC is still reliant on the copper wire. It's not Fibre to the Premises. Unfortunately Openreach have installed a Fibre cabinet that is around 320 meters away from my property. The length is still pretty long considering that I have waited more than 10 years for Fibre.

The cabinet is located in 46 Frostic Walk, Shadwell, London E1 5LT. While the BT Exchange is located in Jerome Street, Bishopsgate, London E1 6NJ.

Because the copper cable on ADSL is going via Jerome Street to my property in Commercial Street, this extends the copper length to around 1000 meters in length for ADSL.

There was another electric outage today that has obviously reset the router. There is some construction works in my building for new cladding.

Anyway, the situation is the same.

6 - Uptime: 0 days 07:41:51
7 - Data rate: 1219/14335
8 - Maximum data rate: 1232/16980
9 - Noise margin: 6.5/7.3
10 - Line attenuation: 13.3/25.5

Noise margins have never ever been the same again since 1st of October! As soon as BT Openreach connected this new Fibre Cabinet to my EO Line Noise margins dropped from 9.0dB respectively to 7.3dB on average for ADSL.

Now I know that choosing an FTTC package should most likely improve noise margins as length of copper will be 320 meters vs 1000 meters on ADSL. But I am still wondering why the new cabinet has caused reduced noise margins on ADSL. Lower sync speeds of below 10 Mbps can be observed when Data rate drops to 11440 Kbps something that has never ever been seen before in more than 10 years here in my property. This is directly associated with this new cabinet, no coincidence.

I will switch to a Fibre package and see if the problem will naturally go away. But I still need to wait till January as I paid year upfront, and I don't think I can switch to Fibre without losing some of the upfront cost that I already paid in advance. Plus I don't want to tie into a new contract.

Posts: 3,349
Thanks: 1,109
Fixes: 51
Registered: ‎28-02-2017

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!


Have you looked at the DSLChecker to see what FTTC speeds may be available? If you were to start the upgrade process on the PlusNet website (but not complete it) I believe this would also show the expected FTTC speed.



Plusnet Alumni (retired)
Plusnet Alumni (retired)
Posts: 442
Fixes: 19
Registered: ‎25-09-2018

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

Hi there @serajmi

It's likely that you've paid your line rental up front for a year and got a broadband discount that covers the cost, essentially making it appear you've paid up front for the year.

We don't offer a system where you can pay for the broadband cost up front.

If that's the case, you'd still be able to upgrade if you desired. The annual payment you made for your line rental would be unchanged and whatever time you had remaining would carry over.


In addition, if you're already an existing customer we can't 'upgrade' you to fibre that isn't on a contracted term.

That being said, you'd still get a discounted rate for the duration of the contract.




Posts: 25
Registered: ‎26-02-2019

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

Telephone Number ........ on Exchange BISHOPSGATE is served by Cabinet 20


Featured Products

Downstream Line Rate(Mbps)

Upstream Line Rate(Mbps)

Downstream Handback Threshold(Mbps)

WBC FTTC Availability Date

WBC SOGEA Availability Date

Left in Jumper

  High Low High Low        
VDSL Range A (Clean) 80 68.2 20 19 62.1 Available -- --  
VDSL Range B (Impacted) 80 64.8 20 19 56.6 Available

Hello and yes I have already checked the speeds available. In fact that's what I saw on day 1 in the BT Broadband Availability Checker. I was very much alert from the broadband checker. 1st of October I saw this change for the first time, this coincided with a series of unusual internet disconnections which indicated that BT Openreach were working on connecting my EO Line to this new Cabinet 20.

As soon as I saw cabinet 20 being displayed as served rather than Exchange Only Line, surprise, surprise the noise margins plummeted in the router stats!

7 - Data rate: 1219/14335
8 - Maximum data rate: 1232/16720
9 - Noise margin: 6.5/6.9

I have never seen such dreadful noise margins at that data rate for standard ADSL broadband. But this is directly a result of this new cabinet. ADSL service has been damaged as a result of this new change. These noise margins are meant to be between 9-12 dB at that data rate and not below 7 dB. Hence why my connection is no longer stable, DLM will trigger speed reductions on the next drop-out.

Now I shall see what the performance will be like on FTTC. Lowest speed is 64.8 to 80 Mbps. It's not just a question about being able to attain those maximum speeds. I hope the noise margins will cope with FTTC especially if DLM is a problem.

Some ISP's let you quit penalty free within 30-60 days should I not be able to get at least the lowest attainable speeds and remain stable. My only worry is if following a disconnection due to low noise margins if the connection can't hold those speeds I will have to downgrade to 38 Mbps package. But of-course without trying I won't know. I have zero experience of Fibre broadband, I've never had it in my life yet and I will find out when the current contract runs out.

The real mystery that baffles me is why the noise margins on ADSL have dropped so sharply following this cabinet change. At least the suffering won't last for more than 2 months before I can get rid off ADSL for good! 😌

Aspiring Hero
Posts: 2,738
Thanks: 1,414
Fixes: 59
Registered: ‎07-07-2009

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

First question, why are you obsessed by the signal to noise margins, has the change affected your ADSL service in any way?

It looks like your sync rate is slightly higher with the lower margin so what's the problem, ignore the maximum data rate figures they are just optimal case calculated values that usually can never be achieved. Many ADSL lines operate perfectly well at 6dB SNRM and can also achieve higher speeds at a reduced SNRM of 3dB. Why you think your high SNRM values are necessary or normal is hard to understand. I would say they are too high and you should be getting a higher speed on ADSL.

Second question, why do you think you have to wait to the end of your contract to upgrade to FTTC. PlusNet staff have already stated you can upgrade now, you have not paid for a years broadband up front, it can't be done.

You seem to think that 320 metres to your FTTC cabinet is pretty long, I can categorically say that it is extremely short, many people would give an arm and a leg to be on such a short D-side line length (D-side is cabinet to premises). You are very likely to get 80Mbps with no problem and the SNRM values on ADSL are completely irrelevant when changing to a FTTC service with a much shorter copper line length.

The reason that the ADSL stats have changed is that the line from the exchange has been diverted to the cabinet and possibly increased in length and split up to connect to the cabinet terminations which if you have ever seen inside a phone cabinet are rather like spaghetti which will increase the noise levels on the line.

So if you want 80Mbps go for the upgrade to FTTC, if you don't want higher speeds stay on your existing service.😐


Posts: 25
Registered: ‎26-02-2019

Re: Following Exchange Only Line upgrade to new Fibre Cabinet, ADSL noise margins have dropped!

Of-course it has affected the service! I wouldn't be posting this thread if my internet connection remained stable with those reduced noise margins!

The problem can be seen as evidenced. I'm not making this up.

6 - Uptime:     1 days 00:12:21
7 - Data rate:     1219/14335    
8 - Maximum data rate:     1232/13408
9 - Noise margin:     6.3/1.4

This is what happened earlier morning. The noise margin dropped from 7.3 dB down to 1.4 dB and the internet was completely unusable. No pages were loading despite the router showing as connected.

Then a couple of hours later the internet connection dropped out and re-synced at a lower speed exactly as I have described! This behaviour is not happening by exception, the Data rate is back down to 11958.

6 - Uptime: 0 days 08:33:02
7 - Data rate: 1201/11958
8 - Maximum data rate: 1216/16800
9 - Noise margin: 6.4/11.4
10 - Line attenuation: 13.3/25.5

The problem is that my building and my line cannot maintain a stable connection with a 3dB or a 6dB noise margin profile because when the noise drops it drops by at least 5-6 dB noise margin points causing a complete drop-out of the connection.

I use to sync at roughly this Data rate: 1219/14335 for 30-56 days at a time. Now my connection cannot last for more than 1-2 days following this new cabinet.

Here's my thread from February.

I have had nothing but problems since switching to Plusnet from Sky. Under the EO Line back then my default noise margin was 3 dB and I had to tell Plusnet Support here on these forums to manually cap the noise margins to 9 dB and then the problem resolved itself.

Now as we can see the router fails to sync at 9 dB at those speeds. Now my noise margins are at 11 dB, connection is more likely to be stable but as we can see in speed test I get only 10.30 Mbps vs 12.30 Mbps previously. A drop of 2 Mbps with the new cabinet.

Hence why I am worried that the same problems may be carried forward with FTTC if the connection tries to sync at 80 Mbps with 3dB noise margin profile. My gut instinct says that this is not going to be stable, I don't know why! I'm only positive that perhaps at the lower 60 Mbps it might just be stable, but I don't know.

The building next to me that is KENSINGTON APARTMENTS, E1 6LW on Exchange BISHOPSGATE is served by Cabinet 27 is going to get upgraded with FTTC in January and they are getting much better speeds.

  High Low High Low      
VDSL Range A (Clean) 80 79 20 19 74 Planned Planned  
VDSL Range B (Impacted) 80 78.5 20 19 72.9 Planned Planned

VS speeds in my building that is served by Cabinet 20

  High Low High Low      
VDSL Range A (Clean) 80 68.2 20 19 62.1 Available --  
VDSL Range B (Impacted) 80 64.8 20 19 56.6 Available

They are having a line that is less than 100 meters from the Fibre cabinet. While I am only going to get the minimum 64.8 Mbps at a 320 meter line and who knows if the router will even be able to maintain sync, I remain pessimistic!