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Linespeed slippage

irritablegit
Rising Star
Posts: 63
Thanks: 7
Fixes: 1
Registered: 28-03-2009

Linespeed slippage

From May 2011
I was on "Plusnet Extra Fibre"  ....  "Estimated speed 34 Mbps"
Used Netgear router WNR1000v2 which came from Plusnet
Used BT Openreach modem which was installed (the 2nd replacement) in Aug 2011
The hardware above is currently the same
The only change is since Nov 2012 I've been on "Plusnet Extra Fibre"  ....  "Estimated speed 70 Mbps"
The stats below come from Speedtest.com 
but the Plusnet Linespeed comes from https://portal.plus.net/my.html?action=data_transfer_speed
Date               Ping Download Upload Day Time PN Linespeed
2012 11 23 27 68.88 14.03 Fri 10:00
2012 11 25 26 69.69 12.1       Sun 09:22
2013 01 10 38 69.19 11.02 Thu 07:47
2014 04 14 32 62.06 10.64 Mon 11:25
2014 04 23 37 61.63 11.85 Wed 18:12
2014 04 25 36 61.79 15.13 Fri 07:56
2015 12 01 14 60.55 17.13 Tue 19:00
2016 02 28 13 55.29 17.26 Sun 10:15           58 Mb
It can be seen that the Download speed is roughly in line with the PN Line speed
Clearly the PN Line speed in the past was much higher, although I haven't got the actual figures.
So why has it been sliding down ? 
I can see I'm much better off than a lot of people, but when I'm told 70Mbps - and I used to get about 70 - can anyone advise
a) why it's been sliding ?
b) how to stop it sliding and get it back up to where it's supposed to be ?

7 REPLIES
dnpark38
Rising Star
Posts: 432
Thanks: 16
Registered: 24-02-2015

Re: Linespeed slippage

There is a unit in the BT/OR cabinet called DLM and if anything happen such as a power cut to your router or interference on your line to your house the DLM cuts the speed to protect the line.
Others might well give you a more technical answer.
Sad part is the DLM doesn't up the speed again when the problem goes away, it needs the intervention of PlusNet to up your maximum speed again.
http://www.thinkbroadband.com/speedtest/button/1476198475230638155-mini.png
Community Veteran
Posts: 5,059
Thanks: 426
Fixes: 16
Registered: 10-06-2010

Re: Linespeed slippage

Considering it's over the years, it's probably due to increased crosstalk as more people switch to FTTC. The signals in one line radiate out slightly, which acts as interference on other lines nearby (especially in big cables containing many individual lines), so as more people switch to FTTC, there's more interference, so everyone's speed tends to drop.
There's not much that can be done about crosstalk, although in future vectoring technology might be used, which can mostly eliminate the problem
irritablegit
Rising Star
Posts: 63
Thanks: 7
Fixes: 1
Registered: 28-03-2009

Re: Linespeed slippage

Could I have an official reply from Plusnet please ?
Is it true that DLM only moves the linespeed down ?  And it never comes up again without manual intervention ?
Either way, I'd like it back up where it was because that is what I'm paying for.
I look forward to hearing from you shortly ...
jordanc1230
Rising Star
Posts: 83
Thanks: 21
Fixes: 1
Registered: 05-09-2014

Re: Linespeed slippage

DLM is meant to increase the speed as the line begins to improve automatically. Also it is a common problem that as more people sign up to FTTC in your area your speed drops, most likely as ejs says due to crosstalk.
dnpark38
Rising Star
Posts: 432
Thanks: 16
Registered: 24-02-2015

Re: Linespeed slippage

Yes I too thought it would move speed back up, but that's not the case I'm afraid, I had this confirmed by an OR engineer on Friday.
mav:quote
http://www.thinkbroadband.com/speedtest/button/1476198475230638155-mini.png
Plusnet Staff
Plusnet Staff
Posts: 2,143
Thanks: 371
Fixes: 116
Registered: 22-08-2015

Re: Linespeed slippage

Hello there. Our line speed (or, rather connection profile) changes in response to fluctuations with the sync speed and bandings. The DLM will apply certain speed bandings as it sees fit in order to maintain a stable connection. If DLM applied a low banding, our connection profile would match this.
If there is a fault and it is resolved, the DLM will automatically move the banding up to the correct level, however it can take a few days for these changes to come into effect. Once this has happened, manual intervention is required to up our connection profile.
Here's a handy article on DLM for FTTC:
http://community.plus.net/library/browsing/fttc-dlm-what-it-is-how-it-works/
In regards to the original issue at hand (and solely from the information provided here), I would advise contacting us via webchat to manually increase the connection profile. You would need to either reboot the router or drop the PPP connection through the router interface to accept this new change in speed. If the issue is not resolved, I'd recommend troubleshooting the fault at http://faults.plus.net and then potentially raising this to our faults team to investigate further if necessary.
Hope this helps
From when I joined the Plusnet Help Team in May 2017 my main Community account is @Gandalf.
If this post resolved your issue please click the 'This fixed my problem' button
 Anoush Mortazavi
 Plusnet Staff
dragon2611
Grafter
Posts: 283
Registered: 20-10-2013

Re: Linespeed slippage

Quote from: ejs
Considering it's over the years, it's probably due to increased crosstalk as more people switch to FTTC. The signals in one line radiate out slightly, which acts as interference on other lines nearby (especially in big cables containing many individual lines), so as more people switch to FTTC, there's more interference, so everyone's speed tends to drop.
There's not much that can be done about crosstalk, although in future vectoring technology might be used, which can mostly eliminate the problem

VDSL2 (FTTC) enabling my 2nd line knocked about 4 - 5Mbit/s off the existing line,
The Second line was syncing a fair bit slower, but looks like DLM finally enabled G.INP on it so now they're both about the same.