S/N Margin

[#1]

I was moved over to ADSL2+ a few weeks ago and on the whole am pleased with it. My upload speed has more than doubled and the download is up a little. There is one problem though which is rather annoying. During the day everything is fine but by late afternoon and evening the download S/N Margin starts to reduce and eventually drops to almost zero. Once it gets below about 2.5 - 3 dB, page loading starts to slow down and eventually as the evening progresses stops altogether. Rebooting the router usually sorts it out although the S/N still remains around only 3dB or just over. By 8 the next morning the S/N is up to around 5.5 - 6dB and everything is then fine until later in the day when the whole process is repeated. It seems to me that the target S/N is a little on the low side but nothing I do seems to make any difference. I have tried rebooting at different times of the day and even leaving the router off all night on one occasion but all to no avail. Any suggestions would be welcome.

[#2]

Do you get the same results when connected directly to your test socket (if you don't try it you will never know if your internal wiring is to blame.)
In my case on ADSL2+ the downstream SNRM drops from about 7.8 during the day to sometimes around 4.5 and doesn't cause any problems. Yours is obviously dropping more than that which is probably causing the disconnections. If you have tried the test socket and get the same results you could try re-synching just after the dropping SNR causes a disconnection and then leave the router switched on continuously in the hope that you will "force" a higher range of SNR which will accomodate the lows at the expense of some speed  (you shouldn't really have to do that though and it's possible you do have a fault which needs investigating.)

[#3]

Quote from: custos

I was moved over to ADSL2+ a few weeks ago and on the whole am pleased with it. My upload speed has more than doubled and the download is up a little. There is one problem though which is rather annoying. During the day everything is fine but by late afternoon and evening the download S/N Margin starts to reduce and eventually drops to almost zero. Once it gets below about 2.5 - 3 dB, page loading starts to slow down and eventually as the evening progresses stops altogether. Rebooting the router usually sorts it out although the S/N still remains around only 3dB or just over. By 8 the next morning the S/N is up to around 5.5 - 6dB and everything is then fine until later in the day when the whole process is repeated. It seems to me that the target S/N is a little on the low side but nothing I do seems to make any difference. I have tried rebooting at different times of the day and even leaving the router off all night on one occasion but all to no avail. Any suggestions would be welcome.

I have this, however i have via telnet forced my router to sync with a higher snr level although doing so lowers the downstream connection speed. I have gone from 6mb to 5mb but my snr at present is 7db where it would normally be down at around the 2db mark this time of night. During the day my snr will be over 9db and i have a rock solid connection now so it appears.

[#4]

My SNR dropped below 1.5dB about 7.30 this evening and I lost connection to the Internet. After a router re-boot I now have a lower downstream connection speed but at least the SNR is back up to 6.5dB. If it stays like it is now all will be well but in the past, (usually in the early hours) it has reset back to a higher connection speed (without my intervention) and subsequently a lower SNR again. I assumed to start with that this was part of the 'training' process although it still seems to happen.
To answer JayG, yes I have tried connecting to the test socket - that makes no difference.
I will see what happens during the next 24 hours and report back.
Cheers all....

[#5]

By the way 'WelshPaul' I have signed the petition - my father was a GWR driver!

[#6]

After my switch to ADSL2+ a few months ago, I had the same problem - higher speeds (around 9600Mb/s) and 6db during the day, deteriorating SNR after dark, which in my case led to a resynch at anything down to 7000. Then in the morning it would re-synch at a higher speed again. This went on for over a couple of months. In the last week or so though, the DLM does seem to have got the message and my connection has been stable at around 7300Mb/s for over 9 days.
Quite why it took so long to stabilise I don't know, but I do get the impression that the DLM isn't so eager to ratchet up the SNR target as it was under ADSL.

[#7]

Yes Trevor, your experience does seem very similar to mine. After the re-boot last evening it is up to 9dB this morning with a reduced connection speed of 6,872. As long as it stays like that all should be OK even with the usual 3-4dB drop this evening. It is shame not to to be able to get the higher speed but I would rather have the stability. My problem was/is? that it was not at all obvious was what was happening as most of the time it just slowed page loading and streaming to a crawl. If this really is a normal part of the 'training' process it must cause a lot of frustration, especially to the non technical user.
dick:quote

[#8]

Quote from: custos

After the re-boot last evening it is up to 9dB this morning with a reduced connection speed of 6,872.

If you really want a bit more speed, wait until your SNM drops to 7dB and then reboot your router. Assuming your Target SNM is 6dB this should give you a small speed increase. Just don't try this more than once a day otherwise you're likely to trigger DLM to take 'undesirable' actions. 

[#9]

With ADSL2+ you may also have the option to request a fixed margin, this trial refers: http://community.plus.net/forum/index.php/topic,86875.0.html

[#10]

I had exactly the same problem after about six weeks of ADSL2+.
I had great download speeds (> 7MB), but once evening came the SNR dropped to zero (or even into the minus range) and the only way I could get a usable connection was by rebooting the router. Sometimes I had to do this four or five times an evening.
I raised a problem ticket. I'm not quite sure how it was sorted out in the end (I think they had to do something to my base SNR). I've only had two disconnections in the last eight weeks (one of them manual), and am currently synching at 5.4MB with an SNR of 1-2 db. Not ideal, but better than before.

[#11]

HERE WE GO AGAIN! I have had 5 days with a stable connection of 6,872 kbps and between 5-9 dB SNR. giving a respectable download speed of around 6 kbps. Then last evening, for no reason that I could deduce I lost connection for a few minutes and the router re-synced at a much higher speed resulting in a very much lower SNR.. The last 24 hours has seen a very unstable connection with frequent time-outs while browsing and the need to re-boot the router to restore a usable connection. However the connection speed is always too high and the SNR at times is down to 1 or even 0 and never much above 3. At the time of writing this post the downstream SNR is 0 dB and I will probably have to re-boot in order to send it!. The actual dowload speed is also well below what I was getting with a lower connection speed.

[#12]

It sounds as if DLM has decided your line was stable at your previous target noise margin, so it tried its luck with a 3dB noise margin.
Once it realises it's not stable (either though high error rates or too many loss of sync), it should automatically put it back to 6dB or higher, with an associated drop in sync speed and hopefully better stability.
If that doesn't happen you may be able to get Plusnet to override DLM with a fixed line profile, which will set your target noise margin to say 6dB or 9dB, but I believe it is usually only done as part of the faults process. If DLM doesn't undo its changes automatically, I think it's reasonable to raise a fault with Plusnet.

[#13]

Thanks CX23882. At the moment I can't get it to re-sync at a lower speed and the SNR is hovering around 0. One thing I am not sure is how the SNR reported by the router compares with the one used by BT. How do they measure it? Anyway, I will leave it alone for now and see how it goes.....

[#14]

The SNR shown immediately after reconnecting (from a resync) will be similar to your target margin.

[#15]

I have just had to re-boot again to make this post but the connection speed is still too high and the SNR is only 0-1 dB.