DLM / SN margin problem

I currently have a broadband issue, which I am trying to resolve with my ISP.

Would someone kindly tell me......

Is a down SN margin that drops below 6 (2.1 - 4.4) acceptable with DLM, or �Dynamic Line Management� (I don't have fibre)?

The SN margin was always above 10 before recent changeover to DLM.

ADSL (Sync) Summary
System uptime: 1020:43:02
Modem ADSL (Sync) uptime: 80:07:13
Interleaving: On
ADSL mode: ADSL2+
ADSL settings: PVC:0/38
ADSL line speed (kbps): up 1115 down 9213
Line attentuation (dB): up 23.8 down 43.0
SN margin (dB): up 6.2 down 2.1
Total errors seconds: 403

>>

"The technicians who have been looking at your broadband connection have advised that they could see that you had a stable connection for a number of days and have said that the profile is not causing any issues."

A home engineer visit has been offered, but I've already had a number of these in the past.

Edited by deleted (Thu 24-Nov-16 11:58:38)

If it is very close to 3dB immediately after a reconnection, then DLM has decided your line is very stable and has lowered the connection-time margin from 6dB to 3dB. In which case it is reasonable for it to drop as low as 2.1dB with no problem.

If it did make that change, you should have received a significant speed increase at the time. Possibly as much as 1,000kbps.

As Robertos suggests - no problems.

I had an ADSL2+ line with about 46dB of attenuation - so a little longer than yours. It was very stable with a 3dB SNR and would stay in sync for months without a problem and minimal errors. In that time the SNR would vary a little - up to 4dB and down to 0dB.

If the stats are correct with a 80 hour sync and just 403 error seconds - there is certainly nothing to worry about; it is clean and stable. The 9.2Mbps downstream is good too.

Thank you for your help RobertoS.

At times both up and down SN margins have been at 6.0.

I haven't seen any significant speed increases. Reconnections happen in the middle of the night.

What should I do?

Thanks for the information MHC, that makes me feel better.

Do many non BT customers have DLM? Do they have this system in other countries?

Edit: Sorry, to make clearer.....just realised you probably live outside the UK where I am.

I previously read that an SN margin below 6 is bad and can lead to stability problems / loss of broadband connection, that's why I was concerned.

I previously had a long term intermittent loss of broadband connection problem, I don't want that again......it was finally rectified after numerous engineer visits when BT changed the aluminium cable to copper.

Edited by deleted (Thu 24-Nov-16 13:03:23)

If DLM sees a super stable connection, it will eventually do it's final tweak and drop your line down to a 3db target SNR ..........

This will possibly give a little instability, in return for a little more (around 800Kbps) sync.

In my experience some routers don't do so well on this, especially Cisco routers.

Thank you for your help Zarjaz.

I see.

I want stability over speed. I asked for my profile to be put back to what it was pre DLM, was told it couldn't be done.

Is DLM available outside the UK?

My ISP has sent me their new 'Super Router' (not yet used).

Edited by deleted (Thu 24-Nov-16 13:46:27)

I want stability over speed. I asked for my profile to be put back to what it was pre DLM, was told it couldn't be done.

Usually the ISP's want an SFI visit from Openreach, the visiting engineer can then ring and have the target SNR 'hard pinned' to 6db ..... A waste of time and resources, but hey, that's the beaks.

Is DLM available outside the UK?

This is your second mention of this, are you NOT in the UK yourself then ?

If so, then the above is not so useful as the advice I gave is based on a BT Wholesale based ADSL service.

In reply to a post by EloiseJane:

Is DLM available outside the UK?

I'm pretty sure that BT's DLM is their own invention, and not available anywhere else, inside or outside the UK.

However, the principle of dynamically managing the line profile is well understood, with many different techniques built into the standards. The broadband forum has this document describing some of the individual techniques, while the UK's NICC has a couple of documents about their use in the UK: this (2010) and this (2015).

There is one company that implements their own system for dynamic line management is Assia, with their DSL Expresse system. That company was created by one of the original inventors of ADSL, and has been in patent fights with BT over the DLM process.

Vendors of DSL equipment usually have their own network management equipment. Nokia/Alcatel/Lucent appear to have their own dynamic line optimisation tools, for example.

Do you have any stability issues on your line? As Zarjaz says, it will only move to 3dB on a very stable line, if it detects instability over a certain limit it will then revert to 6dB anyway. As I commented before, your uptime is high and very few errors suggesting a stable line.