High SNR margin after very brief powercut

davidw87 — Thu, 22 Apr 2021 22:41:55 GMT

I have BT Fibre (FTTC) using a TP-Link router. The service went live, on a line which hadn't previously had a broadband service, in early April. Everything was fine for 2 weeks and the sync with the exchange was the maximum possible with a decent SNR margin (about 6).

Last week there was a very slight powercut, enough to lose sync with the exchange and flicker lights but not reboot the router. Once resynced, the SNR margin increased to 16 and the speed lowered.

I rebooted the router the next day and it reconnected at a higher speed again with a noise margin of 6. However the following morning, another resync occurred and the SNR margin increased to 16 again. I tried rebooting but the SNR margin didn't go down that time.

It remained connected for a couple of days at the same speed and SNR margin, then resynced in the early hours of this morning, again with an SNR margin of 16 and the resulting 'low' speed.

I've checked all the usual things - quiet line test, etc. - and the router stats (see below) are good.

Does anyone know what could've caused the SNR margin to suddenly increase such a lot? Was it the very brief powercut? If so, how long will it take to reduce back down to 6?

Thanks.

Downstream
Current Rate (Kbps) 27398
Max Rate (Kbps) 59565
SNR Margin (dB) 16.9
Line Attenuation (dB) 9.5
Errors (Pkts) 0

Upstream
Current Rate (Kbps) 9999
Max Rate (Kbps) 20496
SNR Margin (dB) 13.4
Line Attenuation (dB) 19.3
Errors (Pkts) 0

Re: High SNR margin after very brief powercut

NeilO — Fri, 23 Apr 2021 09:17:12 GMT

@davidw87 welcome to the community and thank you for posting, I'm sorry to see you're experiencing problems with your broadband connection.

The disconnections then the reboots have likely caused dynamic line management (DLM) to take action on the line to try and stabilise it. It's not recommended to reboot the router too often as this can trick DLM into thinking the disconnections are worse than what they actually are.

If the line is stable and you don't reboot the router it will reduce the SNR on its own but it can take a couple of weeks.

Thanks

Neil

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High SNR margin after very brief powercut

Re: High SNR margin after very brief powercut