Three is no 9dB noise margin target on FTTC.
The default is 6dB.
ECI cabinets are all stuck on 6dB at all times.
Huawei cabinets can lower the SNRM to 5, 4 or 3dB if a line is stable enough.

The line you're commenting on is within its estimates.
Everyone can't insist on getting the higher end of the estimates.

If/when you decide to place on FTTC order they will quote you a high and a low estimate and a minimum guarantee.
If the low estimate isn't good enough for you then don't order it.

My estimates climbed when the 3dB profiles were rolled out from a High/Clean of 40Mb up to 48Mb so the estimates already take in to account possible improvements by DLM.

The OP isn't complaining about low Speed but that DLM often changes between 3,4 and 5dB SNRM targets which initiates a resync.
This isn't my experience of DLM as it would always wait at least a few days before attempting to lower SNRM after it has increased it.

If the OP changes DLM policy/profile through Plusnet as advised their issues will likely go away.

Your over thinking and worrying too much about the stability and reliability of a technology millions use problem free everyday.

As previously mentioned my line is just over 1km long to the FTTC cabinet (1012m and 1024m quoted on separate line tests) and it runs perfectly stable on a 3dB SNRM target.
I get a very respectable 45Mb down 7.2Mb up at the moment.

If you order 40/10 you will get that easy with plenty SNRM to spare.

In all likelihood you'll sync at or near 80/20 if you go for that package.

In reply to a post by BLaZiNgSPEED:

In recent few years Openreach lowered the DLM down to 3dB which coincided with my daily internet disconnections. This is despite my line being EO.

With Sky this happened like 3-4 years ago. I had to call tech support, they sent a Sky Engineer back then and only gave me a new router. The problem did not solve.

It was only until I called again Sky and they manually set noise margin to 9dB and my disconnections stopped.

Openreach didn't introduce a 3 dB target 3-4 years ago.

Openreach DLM is nothing to do with any lines that aren't FTTC.

ADSL and VDSL are somewhat different things for many reasons - my own ADSL was unstable while the VDSL was fine.

I'm not sure of the relevance of any of this to the issue at hand.

Edited by CarlTSpeak (Tue 08-Oct-19 21:10:06)

In reply to a post by j0hn83:

Three is no 9dB noise margin target on FTTC.
The default is 6dB.
ECI cabinets are all stuck on 6dB at all times.
Huawei cabinets can lower the SNRM to 5, 4 or 3dB if a line is stable enough.

The OP isn't complaining about low Speed but that DLM often changes between 3,4 and 5dB SNRM targets which initiates a resync.
This isn't my experience of DLM as it would always wait at least a few days before attempting to lower SNRM after it has increased it.

As previously mentioned my line is just over 1km long to the FTTC cabinet (1012m and 1024m quoted on separate line tests) and it runs perfectly stable on a 3dB SNRM target.
I get a very respectable 45Mb down 7.2Mb up at the moment.

@j0hn83: I wasn't aware that on FTTC there's no 9dB noise margin target! I know I am probably worrying a little bit more than I should.

If 6dB is indeed the maximum cappable noise margin then I suppose the only way it will maintain stability is if the margin on FTTC does not drop down to 0dB. But it also depends on line quality and length. Each case is individual. I know you've told me in the past on these forums that you successfully achieve 45-55 Mbps on 1km line. But it is possible that you are fortunate to not have any issues with noise on the line!

Especially if we consider the length and location of the area. In a busy urban town/city with busy roads, noise traffic, industrialisation, neighbours that can cause REIN, the copper/aluminium line might not be stable. But in a rural area or less central towns and cities where there is large green fields the line is going to naturally be more stable.

The problem I had (it may be purely my experience) but on ADSL my noise margins at 9dB would drop down to 3dB. This can last anywhere between 10 minutes to 2 hours or so before the noise margin bounces back to 9dB. This has always been the case with Sky, Tiscali, Be Unlimited*, Plusnet, etc. Only under the 1Mbps package in 2005 my connection was stable.

Under ADSL my line will drop out with a 6dB profile! Because in my case there are 5-6dB points lost from observation and usually only in mornings. If the line holds to 1-3dB my line will be stable and the connection will remain in sync for at least 30-60 days at a time. But not always under 6dB my noise margin will drop only down to 1dB it sometimes completely goes to 0. But with 9dB my noise margin during a drop will at least not drop below 3dB.

If the OP changes DLM policy/profile through Plusnet as advised their issues will likely go away.

Your over thinking and worrying too much about the stability and reliability of a technology millions use problem free everyday.

This is why I cannot necessarily guarantee that the OP will have the line stable even under 6dB unless their noise margin only drops slightly and then bounces back to 6dB without it affecting the connection.

Millions of people don't have 1km copper lines under FTTC at least, this is why most people don't have problems! I never had problems in my other flat for 4 years where I lived in Shadwell connected to Stepney Green Exchange and that was only 0.3 miles to exchange and connection was always rock solid.

In my other property where I rent out in Shoreditch cabinet is only 32 meters to property no problem there. Of-course I'm going to see when I do order FTTC finally in January and hope my connection will not drop out with 3dB or 6dB. At least a large chunk of copper (over 600+ meters) will be reduced in my case.

Anyway, thank you for the reassurance, but I am still a little bit worried and I hope the OP solves his problem soon!

There are probably more serious issues than this facing us all. If you do have a need to worry and over-analyse things there might be better targets than an SNR margin.

Well said.

Updated: Engineer found no fault. SAying it was DLM trying to stable the line at 3dB and it moving around itself, nothing they can do about it. So, my parents has decided to downgraded to 40/10 instead of 80/20 and Plusnet offer them a goodwill gesture of having 40/10 unlimited fibre, line rental and anytime calls plan for just £20 a month for 12 months. (free of charge anytime calls plan for 12 month) so can't complaint.

In reply to a post by CarlTSpeak:

In reply to a post by BLaZiNgSPEED:

In recent few years Openreach lowered the DLM down to 3dB which coincided with my daily internet disconnections. This is despite my line being EO.

With Sky this happened like 3-4 years ago. I had to call tech support, they sent a Sky Engineer back then and only gave me a new router. The problem did not solve.

It was only until I called again Sky and they manually set noise margin to 9dB and my disconnections stopped.

Openreach didn't introduce a 3 dB target 3-4 years ago.

Openreach DLM is nothing to do with any lines that aren't FTTC.

ADSL and VDSL are somewhat different things for many reasons - my own ADSL was unstable while the VDSL was fine.

I'm not sure of the relevance of any of this to the issue at hand.

They didn�t introduce a 3dB default, but they introduced the possibility of a 3dB margin about 3 years ago in some cases. Why do you think they didn�t? I remember reading about it at the time.

But yes obviously only on DSLAMs controlled by Openreach, FTTC ones then.

Edited by deleted (Wed 09-Oct-19 19:16:55)

https://www.ispreview.co.uk/index.php/2016/11/speed-...

It was indeed being trialled on a small scale 3 years ago.

I didn't see any cases of sub 6dB lines till the trial was extended in early 2017. Though I say many who thought they were.
Full rollout began 20th March 2017.

I remember a very spirited debate at the time on the effect of lower target SNRM's on the reported max attainable rate

I argued you can use this to differentiate between lines on the trial and those that simply synced pre-crosstalk at a higher rate with a lower actual SNRM.

https://forums.thinkbroadband.com/fibre/t/4528246-op...

I'm still none the wiser on the effects of the SNRM target on the attainable rate on ADSL which obviously works in a different way.

WilliamGrimsley's line 1 of the the 1st I witnessed the 1dB incremental drops, with subsequent attainable increase, as we see in every line with XdB today.

I still frequently see users who randomly sync higher, with a current 3dB SNRM and assume it's a target SNRM set by DLM.
Still never seen DLM jump from 6dB to 3dB though, always in 1dB increments at least 24 hours apart.

I just read most of the trial thread I linked above.

Whatever happened to WWWombat? A great source of knowledge!

I think his solution is banding.

If I remember right when I read one of BT sin documents years ago in the early FTTC days was something in there that isps can request a line to be banded. This would artificially keep the SNRM high providing the capability of the line doesnt significantly regress.