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Serious drop in upstream sync & SNR after rain

pacem
Grafter
Posts: 175
Registered: 07-09-2007

Serious drop in upstream sync & SNR after rain

I have been recording the up and downstream SNR and sync speeds on my router every minute for a couple of months now, and have written a little php script to plot them. The hourly updated graph is available here: http://ccgi.pacem.plus.com/router.php but you'll need SVG support in your browser. FF is fine but IE users may need to download a simple plug-in from http://www.adobe.com/svg/viewer/install/

and when it rains I have problems.

After a sustained rainy period my upstream sync has dropped from 448Kbs to 192kbs, at the same time my upstream SNR has dropped from a healthy 16dB to a paultry 7dB. See Friday on this chart:
http://ccgi.pacem.plus.com/router.php?days=7&day=25&month=2

My line is very stable, as can be shown by the monthly chart finishing on the same day; just one adjustment in downstream speed for the whole month (note the virtical line is automatically added to show any changes in sync - it is not a drop):
http://ccgi.pacem.plus.com/router.php?weeks=4&day=25&month=2

Moving on to today (wednesday 28th Feb) we can see that the rain continued and the sync problem continued. Also worth noting is that the downstream sync and SNR are not affected. I suspect that this means there is a fault on the line near the exchange.
http://ccgi.pacem.plus.com/router.php?days=7&day=28&month=2

The last time this happened was what caused me to write this program. Unfortunately at that time I didn't have any rainfall data but I assure you it was wet:
http://ccgi.pacem.plus.com/router.php?days=7&day=17&month=1

Everytime I asked for help PN were very dismissive, but now I have all the evidence. (Yes I've tried connecting directly to the master socket and any resyncs tonnight will be caused by that. I'll also note here that I don't show the attenuation because it never fluctuates by more than 0.5dB at 59.5dB and 30dB down & up respectively it is all recorded for those that are interested: e.g. the drop on Friday 23rd Feb is in http://ccgi.pacem.plus.com/output-054)

Can anyone shed any more light on this before I get PN to send an engineer who will no doubt turn up after severy dry days and suggest that the fault must have been my wiring...

Paul.<><
3 REPLIES
Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

Serious drop in upstream sync & SNR after rain

Hi,

I'll be 90% certain that the copper cable is damaged somewhere, probably somewhere underground and the duct is getting flooded causing a loop on the line or a crossed line. The problem is trying to find exactly where that it. I've just run a woosh test on the line and it's showing an upstream rate of 192kbps with an SNR of 23dB. I'll try the full one shot test and see if that comes up with anything else.
Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

Serious drop in upstream sync & SNR after rain

No obvious faults showing up on the test but the recommendation from BT is

Quote
All tests OK. Ensure user has all equipment properly connected and that wiring is OK. If all correct, retest, if same result, ask EU to power off modem and retest. If problem still persists, report fault to BT


So I suggest checking what they suggest and then raise fault and put all the information in and we can get it raised.
pacem
Grafter
Posts: 175
Registered: 07-09-2007

Serious drop in upstream sync & SNR after rain

Grr typical. Restarting the router forced a resync and now my upstream sync and SNR are back to normal. I've experienced this many times before. Restarting when the fault occurs doesn't make a difference but after a day or so restarting shows a steady improvement over time. Leaving the router to itself takes slightly longer before things recover.

The woosh test result is interesting because it tells me that my router doesn't update it's upstream stats very frequently. It was synced at 192kbs but thought its SNR was still 7, when infact it was 23dB, that would explain why forcing a resync moved them back to 448Kbs and 16dB. (a 7dB drop would hold with a 2-&-a-bit times speed increase)

Now what do I do?
Is there any point having the line looked at when things are working? I suspect the window for catching a fault is relatively small.

I was hoping to get this problem fixed before tackling the problem of my SNR being too high which is holding back my sync speed; I used to get 2 - 2.5Mbs

Anyway, thanks dtomlinson for the very quick resonse. If only I wasn't on holiday over that weekend.


Paul.<><