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Target SNR shoots up after one loss of sync?

LittleReggie
Grafter
Posts: 54
Registered: 20-11-2008

Target SNR shoots up after one loss of sync?

hello.
after 90 hours of stable connection at 4320kbps and 6db snr i have managed to get my line profile back up to 3500kbps.
this morning, it appears i have had a loss of sync, and my snr has gone straight up to 12db and my router has only synced at 3424kbps. i imagine this is going to drop my profile down to 2500 with consequent loss of speed.
i am surprised that my target snr has increased so quickly after one dropped connection. i am also surprised that despite the loss of sync, my router is still showing that my WAN connection has been up for 95 hours. is this normal?
thanks,
reg.
9 REPLIES
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re:Target SNR shoots up after one loss of sync?

Hi there,
It does sound a bit strange that the target SNR has gone up after a single resync.
Do you hear any noise on your phone line when you plug a telephone into your master socket via a filter?
LittleReggie
Grafter
Posts: 54
Registered: 20-11-2008

Re: Target SNR shoots up after one loss of sync?

james,
thanks for helping (as ever).
there is no apparent noise on my phone line. i also have adsl nation microfilters on my phone and router connections. i did a quiet line test when i installed these, and the line was as clear as a bell.
however, i do live in an area where the electricity supply is a bit unreliable. it can go off unexpectedly, often several times in a short period. then it will be fine for weeks or even months. the last time this happened was about a month ago - could this have a long term effect on my target SNR, with the exchange seeing multiple disconnections of my router?
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re:Target SNR shoots up after one loss of sync?

Potentially yes.
The DLM is probably seeing it as a flapping line.  However, if it remains stable, it should automatically decrease the SNr, although this can take up to 4 weeks.
LittleReggie
Grafter
Posts: 54
Registered: 20-11-2008

Re: Target SNR shoots up after one loss of sync?

hmmm, ok.
do these error stats tell me anything useful? router been up for 100+ hours.
Connection Rate:  3424 Kbps
Line Attenuation: 49 dB
Noise Margin:    11 dB
Interleave CRC:  88
Interleave FEC:  15604
Interleave HEC:  0
Fast path CRC:    0
Fast path FEC:    0
Fast path HEC:    0
Superframes:      2548132
wisty
Pro
Posts: 453
Thanks: 57
Fixes: 4
Registered: 30-07-2007

Re: Target SNR shoots up after one loss of sync?

Has the target SNR actually risen to 12dB or is that simply what your router is now reporting as the current value. The routers reported SNR only matches the target  just after a resync. At other times it will vary depending on the level of the ambient electromagnetic noise.
It's possible that your loss of sync occurred in the middle of the night when noise levels rise and the SNR drops as a consequence. My SNR regularly drifts down to 2 or 3dB at night. If it dropped too low and you got a resync event, the router and exchange would have negotiated a speed that gave a 6dB SNR at the time (when noise levels were high). When the noise levels dropped as daylight came, the SNR would naturally rise again and go higher than 6dB given the lower sync speed.
The only way to check is to reboot/reset the connection when noise levels are lower. If it re-syncs at a higher speed and 6dB then the target is still 6dB and the resync occured during a noisy period. If it still resyncs at the lower speed and 12dB then the DLM has altered the target.
LittleReggie
Grafter
Posts: 54
Registered: 20-11-2008

Re: Target SNR shoots up after one loss of sync?

yep. i know exactly what you mean.
the resync occurred at about 6.30am. i looked at the router at about 8.15am and it was showing 13db. from experience, i dont think the router could have synced at anything lower than 12db.
it is now (7.20pm) showing about 8db. this is the sort of fluctuation i would normally see, but it would usually be reading 2-3db at its lowest point at this time. i have seen it go down to 1db before, but the netgear normally holds the connection at this snr, and even lower.
regards.
Community Veteran
Posts: 26,529
Thanks: 766
Fixes: 9
Registered: 10-04-2007

Re: Target SNR shoots up after one loss of sync?

Quote from: LittleReggie
however, i do live in an area where the electricity supply is a bit unreliable. it can go off unexpectedly, often several times in a short period.

Have you thought of investing in a UPS?
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)
LittleReggie
Grafter
Posts: 54
Registered: 20-11-2008

Re: Target SNR shoots up after one loss of sync?

Quote from: jelv
Have you thought of investing in a UPS?

it had crossed my mind, and i havent completely dismissed the idea. but i cant help thinking that would be curing the symptom rather than the cause of the problem. i should really get onto sweb (or whatever they call themselves these days) and make them aware of the problem, if they arent already. one of the downsides of living off the beaten track i suppose. Wink
reg.
wisty
Pro
Posts: 453
Thanks: 57
Fixes: 4
Registered: 30-07-2007

Re: Target SNR shoots up after one loss of sync?

Could well be the response of the router to a power glitch or two.
My worst experience with SNR being reset was caused by a power glitch. My Netgear router got itself into a twist, continually dropping the line, then reconnecting about once every two minutes. The DLM got really upset. I had to power cycle the router to stop it, and get Plusnet to reset the SNR.
My line will usually hold a stable connection day in and day out at speeds just above the 6240 figure that supports a 5500 BRAS even though the SNR fluctuates between 6dB (day) and 3dB (night). To keep it this way I use the DGTeam firmware set up to reconnect at about 60% SNR. If a drop happens at night when things are noisy, I get a reconnect at about the right speed and 3.8-4dB. If the drop happens during the day, I CAN see link speeds over 7400 with SNR of 3.8-4dB, but when it goes dark the system drops back to 6300 ish. This process preserves my 5500 BRAS across the occasional line drops.
My neighbours typically run the 4500 BRAS that results from 6dB reconnects  during the evening and which I would have without the DGTeam firmware.