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Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

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Dabbler
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Registered: ‎25-02-2020

Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

I've noticed over a period of months that my VDSL link speed as reduced, with a corresponding increase in the noise margin, presumably because DSL thinks my line is unstable.  Here's my current router stats:

 

DSL Link          Downstream Upstream
Connection Speed  25.00 Mbps 8.03 Mbps
Line Attenuation  26.60 dB   26.20 dB
Noise Margin      12.90 dB   5.90 dB

 

 

When checking back through my router logs, I can see the occasional link drop, usually only once every 2-3 days, but it varies, and almost always overnight when I'm not even using my broadband.

 

My link used to sync at ~39Mbps with a noise margin of ~6dB, but that was many months ago now and I don't have any output to hand.  The link resets have also been happening for a long time (months), and while they themselves are not causing me any problems, the drop in bandwidth is. 

It's worth noting that I actually have a second (business) fibre broadband link coming into my property from another provider, and this has been completely stable.  (The link up time is >47 days, which is almost certainly when the router was last rebooted.)

I also replaced my Plunet Hub One router with a Netgear Nighthawk D7800 in effort to try and resolve the link issues and improve my wifi, but this has not helped with the link problems.  (The wifi is much better.)  Both the original Plusnet router and the Netgear router were/are plugged in to the (NTE5 filtered) master socket.

The fact that my 2nd line doesn't experience these issues, and that the issues remain even after replacing the router leads me to think that this problem is most likely to be external, perhaps back at the cabinet or the exchange.

I believe it's now possible for Plusnet to perform a DLM reset, which might help me in the short term, but I'm guessing DLM will once again attempt to "improve" my link stability by increasing the target noise margin.  It's not actually improving the link stability, it's just reducing my bandwidth.  Can the noise margin be fixed at 6dB?

Any advice would be appreciated.

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Dabbler
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Registered: ‎25-02-2020

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

Update:  My line is still syncing at exactly 25 Mbps downstream, with a noise margin of ~13dB, and has been like this for a few weeks now.  Here's the latest router stats:

 

DSL Link Downstream Upstream
Connection Speed 25.00 Mbps 8.02 Mbps
Line Attenuation 26.30 dB 26.00 dB
Noise Margin 13.20 dB 5.90 dB

 

Reading other posts here, I get the impressed my line had been banded, and I'm never going to get back to the ~39Mbps I used to have many months ago without someone taking some action.

Would someone from Plusnet be good enough to take a look at my line and remove any banding?  I'm gussing it would also be worthwhile running a line check to see if we can get to the root cause of the infrequent line drops, which I'm assuming have triggered DSL to reduce the line rate and resulted in my line being banded?

 

Thanks, Alex

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Plusnet Help Team
Plusnet Help Team
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Registered: ‎23-12-2019

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

Hi @arooney

 

I am sorry to hear of the problems with your broadband. I have tried to call today but was unable to get in touch, sorry I missed you.

 

The purpose of DLM is to pick up on a fault on the line and cap the speeds in order to stabilise the line. However, I have tested your line today and have been unable to find a fault that would be causing any problems.

 

In addition, to this, I can see that the sync speeds are above the minimum guaranteed for your line. I have detailed my test results on your account which you can view here. I have raised this to our suppliers who will complete automated testing on the line, but we may need to arrange for an engineer to visit to fully investigate this for you.

 

If you could respond to the ticket online, I'd be happy to progress with this for you. 

If this post resolved your issue please click the 'This fixed my problem' button
 Katie C
 Plusnet Help Team
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Champion
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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

The constant sync speed of 25Mbps and high snr margin looks very much like a banded line to me, I would have thought @KatieC would have spotted this. The line needs a DLM reset first, which PlusNet can request. I would not bother with an engineer visit at this stage, The banding should show up on the downstream speed profile reported on a GEA test.

The fact that the line is syncing above the minimum estimate for the line is meaningless and irrelevant. 

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Plusnet Help Team
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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

Hi @RealAleMadrid

 

Thank you for your reply!

 

I can confirm that the connection isn't banded, the current profile in the GEA test is above the sync rate for the line, this was already checked before I requested the engineer visit.

 

If the SNR has increased this is normally caused by an issue on the line, this is the reason why I've requested for an engineer to investigate. If it is the case that the DLM has to be reset then this is something that the engineer can arrange. Unfortunately this isn't something that we're able to request remotely in this situation.

 

I raised the fault with our suppliers so that we can progress with a resolution. However, as there was no fault found when testing, they automatically request for an appointment to be booked with the end user. This isn’t something we can get around, as if the appointment isn’t booked an engineer won’t attend. This doesn’t mean that there isn’t a fault, it’s just that our testing isn’t picking anything up.

 

Please let us know if you have any further questions!

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 Katie C
 Plusnet Help Team
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Dabbler
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Registered: ‎25-02-2020

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

Hi KatieC,

Thank you for checking the line and opening up the case for me, that is appreciated.

Just for reference, the current downstream connection speed I see on my router is still exactly 25.00 Mbps (as it has been for a number of weeks now):

 

DSL Link Downstream Upstream
Connection Speed 25.00 Mbps 8.00 Mbps
Line Attenuation 26.30 dB 26.00 dB
Noise Margin 12.90 dB 5.90 dB

 

This seems to exactly match the top end of the downstream rate in the profile name (from the GEA Test Detail):

Profile Name 0.128M-25M Downstream, Retransmission High - 0.128M-10M Upstream, Error Protection Off

The profile details above appear to imply that the line is limited to a maximum of 25Mbps downstream, or am I mis-interpreting this?

If you are sure that the line is not banded, then I will respond to the case and we can schedule an Engineer visit.

Regards, Alex

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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

@arooney 

I don't know what GEA test information @KatieC is looking at when she states


@KatieC wrote:

I can confirm that the connection isn't banded, the current profile in the GEA test is above the sync rate for the line, this was already checked before I requested the engineer visit.

 


The line is obviously banded, the sync rate is at the maximum profile speed of 25Mbps as I suspected in my previous post.

You say your sync speed has been at this level for some time, one thing you have to look out for on GEA test results is that the Profile data is usually about 2 weeks out of date ( it might be 13 days, I'm not certain) The time stamp on the Profile section of the test will clarify this. Perhaps this is causing some confusion but the line is definitely banded.

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Dabbler
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Registered: ‎25-02-2020

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

@RealAleMadrid - thank you for the comments, appreciate you taking an interest and trying to help resolve the issue.

 

@KatieC - could you please review the connection again for me?  I'm happy to arrange an Engineer visit, but it really does seem like this line is being artificially limited to 25Mbps.  The line used to sync at ~39 Mbps (many months ago) and has stepped down at least a couple of times in recent months.  It has been running at 25Mbps for quite a few weeks.  (I can't remember for exactly how long, but it's certainly more that 2-3 weeks, I suspect much longer.)

 

Regards, Alex

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Plusnet Help Team
Plusnet Help Team
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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

I think there has been a little confusion here. Katie's was correct in her suggestions going forward.

 

The sync test that Katie ran showed that the line sync rate (23Mbit) was below the banded rate (25Mbit), hence us sending to Openreach to remove banding is likely to fail - hence the request for the engineer visit.

 

I'm willing to give it ago, indeed, I've filled in the details already, but I don't want to delay you.

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 Tony T
 Plusnet Help Team
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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

@plusnettony 

This is another oddity of the GEA test, if the line is on retransmission high the test reports a reduced sync rate, the actual sync rate reported by the modem is 25Mbps, look at the downstream line rate figures on the GEA test I expect they will show 25Mbps.

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Dabbler
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Registered: ‎25-02-2020

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

@plusnettony if you could go ahead and remove the banding, that would be appreciated. 

 

My router is showing 25Mbps at the download rate, so I'm inclined to believe that the GEA test figures (23.8Mbps) aren't showing the whole picture here, and are somehow being adjusted.

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Plusnet Help Team
Plusnet Help Team
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Registered: ‎24-07-2014

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

I suspect the KBD / GEA tests are a little "old".

 

I've added you to the sheet and we'll see how we get on.

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 Tony T
 Plusnet Help Team
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Dabbler
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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

Hi @plusnettony,

 

Are you able to confirm whether or not the banding has been removed from my line?  

 

As of today, it appears my connection speed has reduced yet again, and my router is now syncing at 22.4 Mbps with an even larger noise margin.  Here are the current router stats:

 

 

DSL Link Downstream Upstream
Connection Speed 22.40 Mbps 8.06 Mbps
Line Attenuation 26.60 dB 26.10 dB
Noise Margin 14.30 dB 5.80 dB

 

If anything, it looks like the banding has become even more restrictive.  Note that the upstream speed remains (and has always remained) reasonable at ~8 Mbps with the expected ~6 dB noise margin.

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Plusnet Help Team
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Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

I'm not in work at present so I can't test the line (one of my colleagues will when they see this post). However, from what you've said, it looks increasingly likely that Katie's suggestion should be done next.

If this post resolved your issue please click the 'This fixed my problem' button
 Tony T
 Plusnet Help Team
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Dabbler
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Registered: ‎25-02-2020

Re: Steadily Increasing Noise Margin / Decreasing Bandwidth - DLM Reset and/or line test

Looks like something has happened overnight/this morning since my previous post.  The router is now syncing at ~33 Mbps with a more normal noise margin:

 

 

DSL Link Downstream Upstream
Connection Speed 33.16 Mbps 8.34 Mbps
Line Attenuation 26.60 dB 26.10 dB
Noise Margin 5.20 dB 5.40 dB

 

I'm guessing the banding was removed last night?  Let's see how things go over the next few days...