Synch Speed reduced after fault resolution

[#1]

Just thought I'd get my oar in here.
I had a speed problem at the end of March, when my download speed fell from over 6000 kbps to under 3000 kbps;  I changed my phone from BT to PN at the same time.  I raised a ticket with PN on the problem but no amount of changing routers, filters or anything else cured the problem; I live only 400 yards from my exchange and all telephone lines have been renewed in the last few years.  I lost connection completely this morning, (don't know why), rebooted my router and decided to check my stats, results here:-
                           Downstream          Upstream    
 SNR Margin  :       13.5                      23.0  db
 Line Attenuation  : 15.0                        8.5  db
 Data Rate              8128                      448  kbps
Having read through the thread, is it possible that BT have messed about with my SNR and attenuation.??  I realise most people would love to have the speeds I'm getting, but it is a bit strange why my speed has dropped by 50% since end of March.   Any comments ?

[#2]

Attenuation no, SNR probably.
If you raise a ticket to us, we can ask BT to lower your SNR for you.

[#3]

@ onlyme:
Don't touch anything!
Your router is syncing at the top-end, with a nice snr!
I suspect your problem will either be IP Profile or RWIN/MTU related.
For your first trick, run the BT speedtester: http://speedtester.bt.com and post the results here.
Secondly, run the Plusnet speedtester at http://www.mybroadbandspeed.co.uk and post the results here.
The combination of those two should allow us to find out why your throughput is low
B.

[#4]

Thanks, James.  Ticket raised No. 24979393.  I live in hope!

[#5]

Quote from: godsell4

The consensus seem to be 10 resyncs in 1 hour will get your profile raised quickly. My experiences suggest BT also monitor some kind of weekly or monthly average too and may increase the margin upwards ... I have never seen the margin automagically reduced. SW.

Now I'm confused. I thought that too many resyncs in what ever time interval automatically got your target SNR changed to the next level (but at 15dB can't get any worse, can it?). I also thought that if you can get your sync speed up by re-syncing (but not too frequently) that will help your profile go back up, but more importantly you need to leave your router on and synced continuously for the fastest result.
@onlyme, @james
The stats show the download data rate 8128, can't get much better than that?
The target SNR might be 15db but what difference will that make James if he's got 8128? If his throughput is only 3M something clearly wrong especially if he hasn't got a stuck profile?
I've just read Barry's post and couldn't agree with him more with my current knowledge. Barry can you fill any of my other queries in this thread? Thanks.

[#6]

@ Barry
Did that this morning, results here:-
BT Speedtester
Test1 comprises of Best Effort Test:  -provides background information.
    IP profile for your line is - 7150 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  8128 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 6306 kbps
If you wish to discuss these results please contact your ISP.
Plusnet Tester
Date Download Speed Upload Speed 
Today 13:06 3208 kbps (401kB/s) 388 kbps (48.5kB/s) Share
Does this help?

[#7]

@onlyme
A high throughput on the BT speedtested coupled with a low throughput on the Plusnet speedtester indicates an MTU/RWIN problem.
Following the RWIN Tweaking guide would be a good start and should enable you to up the throughput considerably.
Note - if this problem recently occurred without you changing anything your end, it may have been some BT maintenance that altered a configuration setting between you and Plusnet.
@Anotherone
The number and type of resyncs that would cause a profile drop is a bit of a black art.  In my experience, anything more than 5 resyncs in an hour would be interpreted by the DSLAM as a problem and the SNR margin will be increased accordingly.  I can't say I've ever seen the SNR margin reduce after an extended period of stability, only by PN requesting it from BT.
It's worth noting that the IP Profile and the SNR margin aren't directly linked.  A one-off resync at a low speed may cause an IP profile of 135k, but won't necessarily increase your SNR margin if the fault is rectified quickly, and without further resyncs.  The DSLAM should notice a one-off low resync and apply 'blip logic' to increase your profile back to normal very quickly (well, faster than the 3-day norm).  I *have* seen this in action where a profile was re-increased within a few hours of a problematic low sync event.
B.

[#8]

Thanks for the info. Barry, and what you've posted @onlyme, that's extremely helpful, filled in a couple of gaps in my knowledge  and experience, quite understand the black art, should help others as well. The RWIN tweaks are something I need to look at for myself soon (it's not a priority issue with me at the mo!).
One thing not mentioned here (or in many other threads - on this forum, must look elsewhere) is to always check that there are no obvious noise problems on the phone line, listen to a quiet line, any noise - report it to your line rental provider. If the noise is intermittent - make sure that you report it WHEN the line is noisey so that the Fault Team can hear it and ENSURE they record it as intermittent, otherwise if an Openreach Engineer turns up and can't replicate the problem you could end up with a hefty bill!! (In the past I've rung BT in the early hours to achieve correct reporting!).
There are occasions when I need to move the router from one part of the house to another (until I can put in some cat5/6 cabling or afford to go wireless!). Is there a minimum time interval to re-connecting (or dis & re-sync) that won't get interpreted as a fault?
Regards,
Chris.

[#9]

@Barry
Did the RWIN tweak and run DrTCP.  Set my RWIN to 18616 as recommended and run the speedtest again, still 3200 kbps.  I'll try again tomorrow and let you know.  The only change made is that I changed phone supplier from BT to PN at the end of March, this was when my speed went down (coincidence ?).
@Anotherone
Hope you did not mind me butting in.  I bet you would like to have my (reduced) speed of 3200 kbps; hope you get your problem resolved.

[#10]

Mine is lower than that at the moment

[#11]

@onlyme
I would recommend that you try an MTU of 1458 and an RWIN of 113440.  If you use a router to connect to the internet, you should also set the MTU to 1458 there.
It is VERY IMPORTANT that after changing your MTU and RWIN using DrTCP that you reboot your computer entirely.  These changes aren't picked up immediately.
B.

[#12]

Might also be worth checking there are no known (admitted by BT ::)) exchange problems?
http://usertools.plus.net/exchanges/

[#13]

Thanks for the comments guys, I'm tempted to reboot my router 10 times in an hour to raise my IP profile quickly but worried my SNR will raise again. My profile is still stuck at 135 kbps as expected.  It's so frurstrating waiting for the IP Profile to update, it's like having a Ferrari in the garage that can only be driven at 5 MPH. My SNR is now 13.5, but I'm still convinced that BT raised my SNR last Friday when they did the manual line test at the exchange. I'm going to wait from my IP profile to get back to something acceptable first then raise a ticket to get the SNR reduced. I also turned interleaving off again yesterday so when that kicks in I should get another 500k on my synch. All this hassle for the sake of a £5 modem cable 
Link Information
   

Uptime: 0 days, 3:40:16

Modulation: G.DMT Annex A [POTS Overlay Mode]

Bandwidth (Up/Down) [kbps/kbps]: 448 / 6,656

Data Transferred (Sent/Received) [KB/MB]: 956.00 / 2.30

Output Power (Up/Down) [dBm]: 12.0 / 19.0

Line Attenuation (Up/Down) [dB]: 11.0 / 20.0

SN Margin (Up/Down) [dB]: 26.0 / 13.5

Vendor ID (Local/Remote): ALCB / ALCB

Loss of Framing (Local/Remote): 0 / 0

Loss of Signal (Local/Remote): 0 / 0

Loss of Power (Local/Remote): 0 / 0

Loss of Link (Remote): 0

Error Seconds (Local/Remote): 0 / 2

FEC Errors (Up/Down): 0 / 0

CRC Errors (Up/Down): 2 / 0

HEC Errors (Up/Down): 0 / 0

[#14]

But note Barry's comments in post #21 about re-syncs per hour.

[#15]

Quote from: tywyn

I'm tempted to reboot my router 10 times in an hour to raise my IP profile quickly but worried my SNR will raise again.

STOP STOP STOP.
Somehow we have got ourselves confused with the 'IP profile' and 'SNR target'.
The best thing to do is leave the router alone and let the BT system sort itself out over the next few days by itself.
SW.