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Author Topic: New connection to FTTC and dropping SNR  (Read 908 times)


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New connection to FTTC and dropping SNR
« on: December 06, 2016, 04:53:00 PM »


No actual problem just an observation on how cross talk and the hack they call VDSL means it will generally decline in speed and/or quality, it's xDSL law. 

Old home, started as number 2 on the FTTC cabinet at 10db SNR full 80/20 with 16db Attenuation, after 2 years SNR was averaging after a gradual decline around 8.2 db when I moved out.  This wasn't too bad really given I was on a street with a further 100 homes running up from where I lived and further down the street towards the cabinet around another potential 60 properties, so lots of pairs in the bundle.

Moved to a new property where the FTTC cabinet has been there for 2 years, with only some Virgin coverage and poor ADSL speeds, so I expect a high take up already and most people who want FTTC have it.

Had FTTC installed just over a month ago at new house, line length shorter than previous property (BT chap said 310 metres, last property was around 350 metres, and new property attenuation showing as 14db, this is on same modem). Sync'd up at 80/20 with 11db SNR, so plenty spare or so I thought, so quite happy.

After keeping an eye on things, a month later there has been several reductions and now on ~8 db (it was 8.5db a couple of days ago), still on 80/20 and no interleaving, but surprised I've not lasted a month without seeing reductions which I assume to be due to cross talk and new subscribers.  The only other thought I had was perhaps tones have been moved around on my line in order to reduce cross talk to others given I had a decent margin, this appeared to happen on the first night with a resync at 4am and small reduction in margin was seen after that.  Transmit power has been reduce as well, but only from 13.3db to 13db so not sure if that can account for all the lost margin.

I've had a play around with wiring and tried a HG612 just to rule out equipment, but can't better anything, so the reduction is definitely external to me.

I'm now monitoring stats (user name Phil2016), I can't see anything untoward on there.

So I hope the gradual decline stops as otherwise I'm going to start losing speed soon. Roll on vectoring, however given I've moved from an ECI cab to yet another ECI cab, that isn't going to happen anytime soon.  :(