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Drop in SNR and Sync Speed

DangerMouseUK
Dabbler
Posts: 18
Registered: 27-01-2015

Drop in SNR and Sync Speed

Hi Guys

 

My line was syncing at the max 79995kbps on the download with an SNR of around 10dbm.

For no reason I could figure out its now hovering around the 75000kbps with an SNR of around 5dbm.

Is there any reason a line can suddenly just change like that.

I asked on Live Chat and they said they couldn't see anything wrong apart from some dropouts today which I explained was me upgrading my routers firmware and changing some settings so beyond that they couldn't really help as the line was within tolerance.


Was wondering if anyone else had any suggestions ?


Thanks

DM

 

From Control Panel:

Estimated line speed:80Mb (This may vary between 68.9Mb and 80Mb) - Checked on 2016-12-16 23:24:06Current line speed:73 Mb

 

6 REPLIES
DangerMouseUK
Dabbler
Posts: 18
Registered: 27-01-2015

Re: Drop in SNR and Sync Speed

Also is there any way to know whether G.INP is on my Exchange ? Or is that G.Fast trial areas only ?

danludlow
Rising Star
Posts: 393
Thanks: 23
Fixes: 1
Registered: 03-12-2014

Re: Drop in SNR and Sync Speed

As I've just replied on another post, I'm getting very similar to what you are experiencing. Also puzzled, and now wondering if there are external changes afoot?

This morning I dropped from the usual 10Db SNR margin down to 3Db, it is currently approaching 6Db having increased throughout the morning. No improvement nor loss of speed noticed as a result. Oookla has been giving odd results at odds with other tests, My service profile has increased 2Mbs on the BTW Performance test.

DangerMouseUK
Dabbler
Posts: 18
Registered: 27-01-2015

Re: Drop in SNR and Sync Speed

Yeah really strange, not sure whats happened on my cabinet.

Community Gaffer
Community Gaffer
Posts: 17,644
Thanks: 636
Fixes: 162
Registered: 05-04-2007

Re: Drop in SNR and Sync Speed

May well be the Openreach 3db trial on FTTC: http://www.ispreview.co.uk/index.php/2016/11/speed-boost-bt-openreach-prep-3db-snr-fttc-broadband-li...

If this post resolved your issue please click the 'This fixed my problem' button
 Chris Parr
 Plusnet Staff
snadge
Rising Star
Posts: 75
Thanks: 9
Fixes: 2
Registered: 10-12-2016

Re: Drop in SNR and Sync Speed

something else to consider (as well as the possibilty of being on BT's 3db trial) is that SNR db can change in real-time if there is noise increases on the line (SNRM going down in real-time without re-sync is a sign of noise increase on the line)

 

also the lower max speed can happen when more people in your post code sign up to fibre, this is because FTTC suffers from crosstalk from neighbouring cables, this is why BT are trialling VECTORING technology which cancels it out, when i signed up 3 months ago the MAX speed was 70Mb... its now 65Mb (im on a 40Mb package so Im ok for now)

jafreer
Rising Star
Posts: 823
Thanks: 48
Registered: 13-10-2012

Re: Drop in SNR and Sync Speed

As you point out Snadge, SNRM is a dynamic value that changes with line conditions. When your modem syncs to the cabinet, it targets a SNRM of 6 dB but that is simply based on the current state of the line. If your line conditions fluctuate then your current SNRM can vary. If it falls low enough, the connection could drop, and when it re-establishes, it will again target 6 dB, meaning you will lose a chunk of speed in the process. If you use some software like RouterStats, you can monitor and graph SNRM to see how much it fluctuates, and also correlate any connection drops with SNRM.

It is a useful diagnostic tool to start trying to figure out what might be going on with your connection.