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[Sonac]

After the storm today and the power being knocked out for hours my modem was able to resync before everyone else. I now have a 1.9dB downstream SNR and a much faster sync speed.

If I keep my line synced like this for the next few weeks will dlm remember my line is stable at this SNR and keep it that way?

Thanks

[RealAleMadrid]

No, it might hang on and stay at that SNR value for a while but will in all probability resync at some point and go back to the usual SNR and sync speeds. It is not a normal operating condition.

[burakkucat]

No. When you next re-boot the modem/router it will re-train using the currently assigned target SNRM.

Assuming you have a VDSL2 (ITU-T G.993.2) service, are connected to a Huawei DSLAM and the DLM has assessed that your circuit can operate with a target SNRM less then 6 dB then today's events will not make any difference. There are just four possible target SNRMs: 3 dB, 4 dB, 5 dB and 6 dB.

Edit: RAM's fingers were quicker at the keyboard . . .

[Sonac]

Ah thats a shame. I usually get 2.9-3.4 SNR. I'll just keep enjoying my extra speed for a while until I get a resync.
Thanks for the response. Getting about 5mbps more than normal!

[burakkucat]

. . . I usually get 2.9-3.4 SNR.

I strongly suspect, therefore, that the DLM process has already decided that your circuit can operate with a 3 dB target SNRM.

[Sonac]

Interestingly enough over the past few hours i've been logging my stats and my SNR has dropped from 1.9dB down to a constant 1.8dB with dips to 1.7dB. With a target of 3db surely it shouldn't be drifting in the other direction? How strange.

[kitz]

>> SNR has dropped from 1.9dB down to a constant 1.8dB with dips to 1.7dB. With a target of 3db surely it shouldn't be drifting in the other direction? How strange.

Not necessarily.    The drop at ~6:30 looks like one of your disturbers has turned on or rebooted their modem. 
- If it's a standard switched on, then its obvious why yours has dropped.
- If it's a retrain, then DSM 'may' have given them a slightly different power profile which in turn could affect your line.   We've theorised before that with DSM it's possible to get in 'power battles' with a neighbouring disturber.    My immediate neighbour is one of my largest disturbers and I've noticed I can pick up different power profiles depending if they are online or not when I perform a resync.  DSM is designed to be aware of any major crosstalkers and adjust power (not just spectral shaping) accordingly.

Not sure what the dip at ~8am is..  but it could just be some type of REIN like activity.    There is obviously what looks some sort of EMI type noise which has temporarily affected your SNR. This sort of behaviour is far from unusual and can happen at any time of the day. 

   

[PhilipD]

Interestingly enough over the past few hours i've been logging my stats and my SNR has dropped from 1.9dB down to a constant 1.8dB with dips to 1.7dB. With a target of 3db surely it shouldn't be drifting in the other direction? How strange.

Just to add to Kitz's good info, your SNR margin will likely continue to drop.  The target is what is aimed for when you first sync up, after that the line will remain connected at any SNR value.  If the SNR drops too low then errors on the line increase and at some point the modem will just give up and re-sync, during the re-sync line conditions are reevaluated and the target is aimed for, and it will sync with your usual 3db margin again.  You will end back where you were before.

Regards

Phil

[Sonac]

Just to add to Kitz's good info, your SNR margin will likely continue to drop.  The target is what is aimed for when you first sync up, after that the line will remain connected at any SNR value.  If the SNR drops too low then errors on the line increase and at some point the modem will just give up and re-sync, during the re-sync line conditions are reevaluated and the target is aimed for, and it will sync with your usual 3db margin again.  You will end back where you were before.

Regards

Phil

Just as you said my SNR held on for a while but I just got a resync. Sad but it was gonna happen. I held 1.9-1.7dB for almost 24 and my line was rock solid until now. Thats quite impressive!



Thanks for the interesting info all.