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SNR up and down irregularly

andrewwhyman
Hooked
Posts: 5
Registered: 16-01-2017

SNR up and down irregularly

Hi all

I've just moved to Plusnet from BT and I thought I'd post this here since BT were completely unwilling to help with anything other than "is it working? OK then what's the problem?". Clearly they've never heard of being proactive!

Below are my line stats, that I have recorded myself using information available from the BT Home Hub over the past several years. The below shows the last month, though this issue began several months ago.

 

As you can see the downstream SNR has been jumping up and down all of the time, and it's not regular. It happens for long periods but it begins and ends at random times. Upstream remains stable.

 

fttc.PNG

 

Whilst my line IS currently stable, clearly there is an issue somewhere, and I believe it could be affecting my maximum speed. I used to get the full 80Mbps, but this has been dropping over time and I've lost almost 10Mbps now.

Here is a graph of the full length of time, since February 2014.

fttc2.PNG

The blue line represents my sync speed and as you can see it has been dropping, except for a short period where it went up to 80Mbps again but then quickly dropped (no explanation).

 

Any ideas what might cause this to happen? I'm concerned that it's going to become a bigger issue and knock the line out.

I'm happy to share privately to Plusnet staff the URL to the graphs for further diagnostic if required.

Thanks

Andy

4 REPLIES
andrewwhyman
Hooked
Posts: 5
Registered: 16-01-2017

Re: SNR up and down irregularly

Bump. Can anyone from staff or anyone who has any idea comment?

Community Veteran
Posts: 5,080
Thanks: 440
Fixes: 16
Registered: 10-06-2010

Re: SNR up and down irregularly

The SNRM going up or down by a few dB could be due to crosstalk, from someone who switches their modem off when they won't be using it for a while. When theirs is on, your SNRM would be lower, when theirs is off, your SNRM would be higher. This is completely normal and not an indication that there is anything wrong.

As more people switch to FTTC on your cabinet, the noise from crosstalk will generally increase, which tends to cause a gradual loss of speed over many months (although the impact on your connection from any one other line can vary substantially, depending on things such as exactly how close together the respective wires are in the cable).

RealAleMadrid
Seasoned Pro
Posts: 684
Thanks: 253
Fixes: 11
Registered: 07-07-2009

Re: SNR up and down irregularly

If what you are seeing is not affecting your service i.e. speeds within estimates then PlusNet will not do anything about it and will not be interested in analysing your data, they probably can't do much as ISPs have very little control over FTTC circuits. There are a number of posts on the Kitz forum where SNRM oscillations have been observed with no logical explanation. If it gets worse and the connection keeps dropping then you should get some help. 

andrewwhyman
Hooked
Posts: 5
Registered: 16-01-2017

Re: SNR up and down irregularly

That's a great explanation and makes complete sense, thanks. All I wanted to know was the reasons behind it and whether it was a developing fault or not. I'm a bit of a data buff so seeing unexplained data bugs me.

Thanks for taking the time to reply unlike BT :-) Already more than happy enough with my Plusnet service (apart from the shaky transfer but that ended up just fine).

Cheers

Andy