Faulty ADSL Filter - How to increase speed + reduce target SN margin

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oliverbartels:
Having identified a faulty ADSL filter as the cause of my low SNR on my line especially at night I am now trying to get my line to connect at higher speeds.

My line attenuation is 59db although I am only 2km from the exchange! BT states I should get about 3.5Mbps. For the first 3 months of my ADSLMax experience I was connected at 1600kbps because my target signal to noise margin was set to 15db due to deterioration at night.

Since I have removed the faulty filter I have connected at about 3100kbps day and night although my SN margin is still 15db.

Can I get my sync SN margin setting changed from 15 back to 9db?

To complicate matters, for the last 2 days my connection speed has dropped to 130.0 kbps on the BT speedtest! Raising a Broadband fault ticket tells me there is no problem with the speed I am connecting at! (the upload speed was 340kbps!)

So, do I just need to get them to 'reset BRAS' or do I have to ask for the SN Margin thing to be reduced seperately?

Cheers, Oli

username: Bartels

kitz:
Your SNR Margin is something that is negiotiated between your router and the DLM on the dslam at the exchange.  This effects the maximum speed which you can sync at.

Now that you have higher sync speeds and if your SNRMargin is more stable, then you can perhaps ask if your Target SNR can be reduced.

Some routers allow you to set this figure youself.

I believe that over time, the DLM should re-evaluate your target SNR but this may take some time, as Ive yet to see anything which states how frequently such things are evaluated.

Resetting the bRAS profile isnt really what is needed here..  your quickest route would either be to change it yourself if your router allows you to do this.. or raising a ticket to PN explaining that you have found the cause of a problem which has caused you to sync at lower speeds than you could have.. and could they please ask if BT could reduce your target SNR.

How maxdsl works.
http://www.kitz.co.uk/adsl/maxdsl2.htm

An explanation of SNR and SNR Margin
http://www.kitz.co.uk/adsl/linestats.htm

Oldjim:
I wish you luck.
My default snr was  increased from 12db to 15db when Plusnet applied interleaving (it was already on but this was part of a check on the Interleave icon) and the senior representatives on this forum advised that there was no means of getting BT to change it.

dusty_bin:
Indeed :(

I've been trying to get PlusNet to reduce my target SNR from 12 dB to 6 dB, but stay interleaved - although I've also said I'd be prepared to accept 9 dB as I can definitely show that that figure is OK, whereas at 6 dB it continues to operate, but I can't show it would definitely sync up without problem at the lower margin.

PN have confirmed my target SNR margin is 12 dB but, given enough patience (and lots of resyncs) I can get the line to sync to 9 dB during the morning and then it will continue to operate roughly in the range 6 to 9.5 dB with a line rate of typically 6720 Kb/s (the figures 5.5 to 9.0 dB in the ticket were at 6848 Kb/s). If I reboot, power cycle, or the line is dropped, it will end up at typically in the range 5152 to 5888 Kb/s (mainly depending on the time of day, I suppose).  My Maximum Stable Rate is 4544 (28/04/2006).

I added a report about 4 pages long to my ticket [20042338] giving plots showing that the line was operating fine as described above and also comparing the results on the extension with that at the master socket - showing there is now very little difference between the two after disconnecting the ring-wire.

Dave Tomlinson, who is usually very helpful, reponded by saying:
"Unfortunately it isn't possible to manually decrease the target SNR. We have requested this on a couple of occassions for other customers but BT were unable to do this for them. They say that so long as the line remains stable the the Dynamic Line Management systems will pick this up in time and automatically reduce the target SNR should the system believe the line will be stable at a lower SNR. They don't give any timescales for what period the line will remain stable though."
It doesn't sound like he is totally convinced by the BTw claim...

so I went back along the lines of:
"I thought the note I put together would have given enough explanation/justification, but here is a shorter version:
1. During training, there was a fault on the line. Training was completed on 28th April, but the fault wasn't cleared until 3rd May. So target SNR, MSR, and fault rate would not have been set correctly.
2. It has been identified that the line performance has been improved further by disconnecting the ring-wire from the extension going to the DTE (if that is the correct term for a 'modem/router').
3. Regular monitoring of the statistics on this line clearly show that operates in a stable fashion in the range 5.5 dB to 9 dB and it has done this for many days. It also shows that it can sync up at 9 dB. Obviously, because of the limitations of the 12 dB SNR margin, I haven't been able to see whether or not it will sync up OK at 6 dB.
4. With the current set-up it is possible to operate the line close to 6.9 Mb/s, but any interruption makes it drop to 5.8 Mb/s or less because of the excessive target SNR. It also means the line cannot take advantage of the 'blip-logic' as it takes several attempt to get it back up to it's normal rate."

I also pointed out an example where someone who had left PN for A&A had been able to get their target SNR reduced.

The respnse I got from another agent was simply:
"Unfortunately, as previously advised by my colleague, this is not something that we are able to do.
We have tried on previous occasions for other customers, to no avail."

So it seems that they are just reluctant because of BTw's typical position on this, and are not prepared to raise the issue with BTw using the justification I've provided for them.

The only drops in speed I have had since the end of July have been due to:
- a power outage
- the authenication problem at PN, so I rebooted my router.
- a problem with data transfer watch incorrectly cutting me of so I rebooted the router.
- last weeks connectivity problem - again I rebooted my router
- a few BT speed tests
each time the initial line-rate got clobbered because of the 12 dB target, and unless I'm very quick, another 3 day wait to get the achievable speed back up.

I haven't had any drops due to the line quality itself and I've got pretty much all the data from my SAR130 at 10 minute intervals, so it's not as there is nothing to back-up the request.

I really think they should be prepared to that this up with the BT client manager as it seems other ISPs can get these changes through the system - so Plus Net should insist on the same.


watcher:
I am in a similar position to yourself.  When ADSLmax was introduced on my line, I had no end of line problems...noise...pops...128K downloads etc.  BT spent 3months+ and 7 engineer call outs dealing with the issue.  Ultimately, it was *MY* suggestion that the internal wiring in the loft, which *BT* put in at the time the house was built, might be the cause of the problem.  The pair into and out of the loft was changed, as was the interconnection box in the loft and Hey presto, the line has now been stable for a month.

But of course all that time when BTs faulty line was giving me issues, interleaving was turned on and default SNRM was set to 15.  Now that the line is cleared, I have no need for either.  So of course I was overjoyed to hear that plusnet was bringing in a portal feature to switch off interleaving at the start of August.  Unfortunately, as it transpires, this "feature" does not apply to 99% of plusnet users that have interleaving...but thats another story, see the appropriate thread.

The general opinion is the the DB can not be decreased, so because of BT's faulty line, I have a ADSL connection that is performing way under its capabilities.  I've got a speedtouch modem, and so can use the excellent DMT tool to get the SNR down to 10Db, which helps. Note that my line has been performing well now for a month, and I have seen no change in SNRM, which calls into question the notion that the SNRM will reduce automatically on a stable line.

But why is it that BT do NOT have in place a procedure to re-tune a line which has been faulty and is now repaired...it is an amazing omission.., and one that any basic engineer would see needs correcting.

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