Oddly low noise margin & high synch speed on router power-up

I normally synch to the exchange at 21Mb with a 15dB line attenuation & 6dB noise margin.

I've had a few powercuts recently and noticed that when power comes back, the synch speed is about 24Mb with a noise margin of 6dB, which then immediately drops to 0dB (or less!). I then manually reboot it and it reconnects at the usual 21Mb speed & 6dB noise margin, which it stays at.

What could cause the router to be synching at 0dB & an extra high speed upon restoration of power? I'm sure it didn't used to do that. The only difference with recent powercuts is that the power's come back on for about 30 seconds before going off again. I guess the 30 seconds could give the router a chance to start negotiating with the exchange again which confuses it when the power properly comes back on?

Edited by deleted (Sat 09-Nov-13 15:45:45)

Lack of cross talk from others who have not restarted at that point maybe

Hi

See the same thing here. I have a UPS so my broadband stays running in the event of a power cut. The last time we had a power-cut affecting the area I was able to drop my connection and reconnect from 14Meg up to 18Meg with the same 6db margin!

Once the power comes back, as modems start to reconnect introducing cross talk again the margin drops causing a resync and it comes up at normal speeds again.

Regards

Phil