Deteriorating ADSL2+ connection and d/l speeds

Hi folks,
I switched to the 'up to 20Mb' Pro package about a month ago and initially achieved a connection speed of around 12.5Mb (9.5Mb d/l speed IIRC), but this has slowly decreased over the last month to around 9.9Mb with a 6.5Mb d/l speed currently, which is exactly the same d/l speed I was getting on my old 'up to 8Mb' Premier package.

I've tried both of my routers (Netgear DG834G and PN-supplied Thomson 585v7) and both give similar results.

Both BT and PN gave an estimated ADSL2+ speed of 14MB for my line and when I posted my stats here a while ago, some of you guys thought I might possibly get even higher than that.

My router stats are currently :

ADSL Link Downstream Upstream
Connection Speed 9891 kbps 448 kbps
Line Attenuation 26 db 6.5 db
Noise Margin 6 db 21 db

I'm pretty sure that something is not right and that my line should support greater download speeds than this. I've raised a ticket with PN but in the meantime, does anyone know what might be going wrong, if anything ?

With your attenuation, a downstream noise margin of only 6dB when connected at that speed indicates excessive line noise. Have you tried plugging your router into the test socket to eliminate your internal wiring as the source of the problem?

Do you get a much higher sync speed if you do that?

Thanks for the reply.

I did as you suggested and got a slightly higher sync speed, so proceeded to experiment to try and find the best combination of socket and router to give me the highest sync speed.

Meanwhile, I received a reply to my question from PlusNet which stated that the reason I've experienced a decrease in speed is because my connection keeps dropping out. It then went on to say that BT's Dynamic Line Management (DLM) will reduce my speed automatically to try get a more stable connection and that the only way to get back to normal is to stay connected for at least 72 hours without any drop outs.

I tend to turn my router off overnight or during the day when it's not required, so I asked if this would cause problems. PN then replied, saying that the DLM is unable to see the difference between the router disconnecting due to a potential fault and me simply unplugging/disconnecting/powering off !

So - in order to maintain a high sync and d/l speed on ADSL2+, it would appear that you have to leave your router on 24/7. Is anyone else aware of this ? This is news to me - turning my router off never gave me problems on ADSL.

I therefore decided to leave my Thomson router connected to the master socket last night and leave it powered on permanently in an effort to increase my d/l speed. (13.4Mb sync speed at this stage)

I checked the router stats this morning, only to discover that my router had disconnected/reconnected at some point overnight and my sync speed has halved to 6.6Mb, with a 5.3Mb d/l speed !

This is now slower than I used to sync at on my old 8Mb Premier account

Has my experimenting lead to a further decrease in speed ? I now don't know what to do for the best - is ADSL2+ really this unstable ? I never had any issues on ADSL, on which I had a rock steady, reliable connection (8Mb sync and 6.5Mb d/l speed)

PlusNet's interpretation seems way off target.

When BT's DLM sees what it considers to be instability it increases the SNR Margin target. The increased SNRM is what effectively lowers the maximum possible DSL synchronisation speed in this scenario.

From your line stats the SNRM is still 6dB as opposed to say 15 or 18dB which would be apparent on a line where the DLM has been doing its evilness.

Hi geetee,

Do you want to drop me a PM with your Plusnet username? I don't mind running some checks from this side to see if I can spot any obvious causes for this issue.

Adam.

Hi,

I think you need to ask mikej for his username not me. I'm not with Plusnet for a start

Just goes to show how kind Plusnet staff are - they even offer to help customers of other ISPs

In reply to a post by mikej:

Thanks for the reply.

I did as you suggested and got a slightly higher sync speed, so proceeded to experiment to try and find the best combination of socket and router to give me the highest sync speed.

Meanwhile, I received a reply to my question from PlusNet which stated that the reason I've experienced a decrease in speed is because my connection keeps dropping out. It then went on to say that BT's Dynamic Line Management (DLM) will reduce my speed automatically to try get a more stable connection and that the only way to get back to normal is to stay connected for at least 72 hours without any drop outs.

I tend to turn my router off overnight or during the day when it's not required, so I asked if this would cause problems. PN then replied, saying that the DLM is unable to see the difference between the router disconnecting due to a potential fault and me simply unplugging/disconnecting/powering off !

So - in order to maintain a high sync and d/l speed on ADSL2+, it would appear that you have to leave your router on 24/7. Is anyone else aware of this ? This is news to me - turning my router off never gave me problems on ADSL.

I therefore decided to leave my Thomson router connected to the master socket last night and leave it powered on permanently in an effort to increase my d/l speed. (13.4Mb sync speed at this stage)

I checked the router stats this morning, only to discover that my router had disconnected/reconnected at some point overnight and my sync speed has halved to 6.6Mb, with a 5.3Mb d/l speed !

This is now slower than I used to sync at on my old 8Mb Premier account

Has my experimenting lead to a further decrease in speed ? I now don't know what to do for the best - is ADSL2+ really this unstable ? I never had any issues on ADSL, on which I had a rock steady, reliable connection (8Mb sync and 6.5Mb d/l speed)

Ooops.

Re trying combinations to see what gives the highest sync, you run a danger of what Plusnet and GeeTee are telling you. Making the exchange equipment think the line is unstable. The probable trigger point is 10 times in an hour.

Have a read of the BT DLM, Noise Margin and IP Profile pages on my website for lots of useful info on all this.

When you have had an overnight disconnection you will probably find from your stats that you have a very high noise margin next morning. If so, at the stage you are at with the investigation of what is going on a reconnection during daylight is needed to get a sensible connection speed back. You also need to read (please post) the line stats taken immediately after that reconnection, to see if the noise margin is still around 6dB or changed.

See "High Noise Margin" in the Troubleshooting section of my site.

Unless the connection time noise margin has been raised, as GeeTee says Plusnet are wrong about not disconnecting. Just don't do it frequently. So off overnight is fine, and also avoids the sort of thing that just happened and has made things worse still.

Even when you get a proper connection speed back by reconnecting, your actual speed will stay low probably for days , as the IP Profile will have gone down. See my reference above to the page on my site.

There are two ways of checking your IP Profile. One is the BT Performance Tester which should be the authoritative but which in its latest incarnation can give spurious results, and your Plusnet control panel which shows the value of the Plusnet copy of the BT one. The two can get out of step .

obviously got geetee's name stuck in my head there for some reason!
Mikek (get it right this time) I've just received your PM now. I'm just about to go off shift so your on my radar to be looked at tomorrow morning.

Adam.

Thanks for the info guys - I'm trying to digest it all at the moment.

My sync speed has halved yet again today to 3Mb, with a 2.4Mb d/l speed - this is getting rediculous now ! I was surfing quite happily at 10MB+ 3 weeks ago with no noticeable disconnections. BT's DLM seems way OTT to me and still seems to be punishing me 2 days after my fault finding (which involved a number of reboots).

I rebooted today and this made no difference to the sync speed - below are my router stats immediately after the reboot, which seem to show an increase in the downstream noise margin of 6 to 27.5dB. Does this show that I'm being hammered by DLM ?

Thomson stats rearranged for easier comparison with my Netgear stats from a few days ago (above) :
Bandwidth (Down/Up) [kbps/kbps]: 3,023 / 448
Line Attenuation (Down/Up) [dB]: 29.0 / 13.0
SN Margin (Down/Up) [dB]: 27.5 / 18.0

It looks like leaving my router on permanently is now making things worse, not better. I might try leaving it on during the day only as suggested above, but I can't help feeling that now BT has decided my line is only stable at 3Mb, it's going to be a slow, painful rise back to 10Mb+

Advice on how best to achieve this would be much appreciated. In the meantime, a reply to my PN question/ticket has asked me to raise a fault, so I'm going to do that in the hope that this may also help.