Very low SNR Margin
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- Re: Very low SNR Margin
Very low SNR Margin
23-10-2012 2:09 PM
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Since my line got upgraded from 8 Mbps after BT upgrades in my exchange (about August 2012), I have had an issue where after a few days, the SNR margin drops to a very low value then the line resyncs back to a lower spped but higher SNRM value.
Currently I have 10941 kbps at 43 db attenuation and 0.9 db SNRM. The RCO is showing as 11784 kbps.
When the line drops, it comes back at about 9148 kbps / 43 db / 4.8 db SNRM, where it remains for a week or two before jumping back to nearly 11000 kbps
The router is a Netgear DG834PN plugged into the main socket with an ADSL faceplate fitted, no other equipment is plugged into the line.
Any ideas if it is a problem with my router, my line or the Openreach Exchange?
Thanks.
Re: Very low SNR Margin
23-10-2012 2:24 PM
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I've looking at the connection logs (as below) the connection looks quite stable at the moment but I can see that the line rate has reduced to 9653kbps presumably due to the previous resynchs.
It's not appropriate for me to go out on a limb but it's less likely IMHO to be the router as you'd more likely be seeing a continual issue. Does your line have a test socket you could connect to whilst we do another test?
Re: Very low SNR Margin
23-10-2012 2:36 PM
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I have removed the faceplate and plugged the router into the master socket. The attachment lists the stats at my end after I reconnected.
Re: Very low SNR Margin
23-10-2012 4:27 PM
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PS as the synch rate is still lower than the IP profile by a considerable degree I'm going to submit an SNR reset now for you.
Re: Very low SNR Margin
23-10-2012 4:49 PM
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I've just seen the line drop and return at 9872 kbps at 7 db SNRM, which is now reducing to 5.4 db
I'll leave it for an hour then put the faceplate back, leave it another hour and plug the phone in, then leave it a further hour and add the call reminder back.
Re: Very low SNR Margin
24-10-2012 9:43 AM
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Reconnected everything last night, and the speed & noise values seem to have remained pretty stable. I'll keep an eye on it for a few weeks, but the jump in speed when I connected to the master socket suggests the filter built-in to the baseplate may be faulty? I'll look into getting a replacement.
Thanks.
Re: Very low SNR Margin
24-10-2012 10:17 AM
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Re: Very low SNR Margin
24-10-2012 3:52 PM
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Actually the situation is more complicated than that as the DLM persists in choosing a D/S SNRM of 3dB which drops to 1dB or even less at night with resulting huge error counts and sometimes disconnections, so I run it tweaked (via Routerstats) to 5dB, although it always resyncs at 7dB before slowly dropping back to the target figure over about a week.
This is not something I feel I should have to do but I'm used to it now and the slightly reduced connection speed and throughput is a small price to pay for very good reliability.
Re: Very low SNR Margin
24-10-2012 7:44 PM
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BT's 21CN DLM is a strange beast...
Re: Very low SNR Margin
08-11-2012 11:40 AM
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I replaced the ADSL faceplate with a new one (from PC Supplies Ltd, via Amazon) and some tones above 328 returned, so maybe the filter built into this one is better than the previous one (that BT supplied and fitted) ?
I use routerstats and can see the SNR change over time, but haven't been able to tie the changes to anything in my household. Waiting to see what happens when the neighbourhood switch on their Christmas lights 😞
Re: Very low SNR Margin
08-11-2012 12:09 PM
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Quote from: ammonyte Hi,
Since my line got upgraded from 8 Mbps after BT upgrades in my exchange (about August 2012), I have had an issue where after a few days, the SNR margin drops to a very low value then the line resyncs back to a lower spped but higher SNRM value.
Currently I have 10941 kbps at 43 db attenuation and 0.9 db SNRM. The RCO is showing as 11784 kbps.
When the line drops, it comes back at about 9148 kbps / 43 db / 4.8 db SNRM, where it remains for a week or two before jumping back to nearly 11000 kbps
The router is a Netgear DG834PN plugged into the main socket with an ADSL faceplate fitted, no other equipment is plugged into the line.
Any ideas if it is a problem with my router, my line or the Openreach Exchange?
Thanks.
I have had a selection of Netgear routers and thomson routers on the same line and all the Netgear routers have displayed this sort of behaviour in that they hang on to the connection like grim death even though the noise margin has reduced to a point where data transfer has slowed down to a crawl. The thomson routers on the other hand take longer to re sync hang onto the connection quite well but if the noise margin falls they release the connection and re sync usually at speeds which are little different from those it was using prior to this time. Overall the most stable connections I had on a line that had a 63db attenuation and a sync that was about 2000kbps came through the thomson routers whilst the fastest connections came from the netgear though the higher speeds were rarely ever held for more than a short time. In the end I put netgear equipment on one side.
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