High noise margin but slow sync speed

[#1]

hi
Until a few months ago, my connection was quite good, with download speeds around 4Mbps or more. However, over the last month or so it has slowed down.
Now, I get consistent sync speeds of around 3000k. The router stats show the following
     
      ADSL Link     Downstream     Upstream    
      Connection Speed       3072 kbps       443 kbps  
      Line Attenuation       32.0 db       15.4 db  
      Noise Margin       27.3 db       27.7 db
With such a high noise margin shouldn't the router sync faster?
My Plusnet profile shows:
Estimated line speed:
5Mb (Accurate to within +/- 1Mbit) - Checked on 2010-12-30 17:13:36
Current line speed:
7 Mb
However, the BT Speedchecker gives the following
Download speed achieved during the test was - 2371 Kbps
For your connection, the acceptable range of speedsis 1200-4000 Kbps.
Additional Information:
Your DSL Connection Rate :3072 Kbps(DOWN-STREAM), 443 Kbps(UP-STREAM)
IP Profile for your line is - 2500 Kbps
The throughput of Best Efforts (BE) classes achieved during the test is - 11.41:21.52:67.11 (SBE:NBE:PBE)
From this, it seems that the IP Profile is right for the sync speed, but I'm not sure where to go from here. Maybe the router has a problem?
Ian S

[#2]

HI IanS,
Definitely the SNR causing the slower speed. Have a look here for some tips on troubleshooting the connection.
Jojo

[#3]

Hi
Thanks for the reply. I've checked most of these, but I'll go back through them again. But I thought that the router should try sync at a faster speed, giving a typical margin of between 6-10 dBs. Isn't that the case?
Ian

[#4]

HI Ian,
The DLM will set a target noise margin in 3dB increments and once that is set the sync rate will be dependent on that. If you can figure out what may have caused this then it's possible for us to reset it back to 6dB but if the problem has not been resolved, doing this can cause more good than harm.
Jojo

[#5]

From a cursory glance, that looks banded to me?
B.

[#6]

It's 20CN Barry

[#7]

I know it goes in 3dB increments, I always though it only went up to 15dB as a targret SNR margin though?

[#8]

ahh, in that case it's probably resyncing during bursts of noise on the line.
Although 15dB is the highest *target* SNR, if the line is very noisy when it resyncs, then subsequently quietens, the reported SNR will increase (as the signal is now so much higher than the noise)
Try to resync the router and see what the SNR Margin is directly after a resync.  Also dial 17070 an choose option 2 and see if there is any noise evident on the line.
Does sound like a fault will need to be raised
B.

[#9]

Hi again
Well, I tried a fferent microfilter, connected to the master socket, different modem cable, all no difference. Still get sync speed of 3072k, whether it's immediately after connecting, or any later time. I don't have another router, so can't change that (I'm using a Netgear DG834PN with latest firmware). Tried the BT quiet line test, nothing obviously wrong (useful tip that, I wasn't aware of it).I don't know what else to try. Basically nothing has changed here with my hardware to cause the problem.Any more suggestions? Should I use the online tool to report a broadband fault?
Ian

[#10]

Lower SNR - Higher Sync Speed.

[#11]

Hi Ian,
If you put it in the test socket and have changed microfilters I can try to reset it.
Jojo

[#12]

Hi
(Finally able to access the internet again after last night's outage!)
Yes, if you please can try resetting it, I would greatly appreciate it.
Ian

[#13]

Hi Ian,
Are you in the test socket?
Jojo

[#14]

Hi
Right now, no, beacause I have to move the PC, disconnect phones etc. But I was yesterday, when I made all the checks suggested in the troubleshooter. Didn't make any difference to the sync speed. Today I have been monitoring the sync speed and noise margins all day with RouterStats, it started at 3072k at 7.30am, and has stayed at that all the time. No resyncing. Downstream noise margin has been 27db all the time too.
Ian

[#15]

HI Ian,
I understand what you're saying but if I reset it while you are not in the test socket then we may achieve nothing. If you can put it in the test socket then I can reset it.
Jojo