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Target SNR changes

SteveA
Community Veteran
Posts: 1,785
Thanks: 98
Fixes: 3
Registered: ‎17-06-2007

Target SNR changes

We had two power cuts this afternoon.

Line came back up with no problems but I'm now seeing something odd on my router:

 

snr1.PNG

My current rates are above the max (the download by a significant margin) and my SNR margin on the download seems extremely low - I thought the target was 3, or has it been moved down again? As you can see there seem to be no errors on the download.

 

The speedtest cli (running from a wired PC) reports

Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by toob Ltd (London) [2.56 km]: 14.812 ms
Testing download speed................................................................................
Download: 46.83 Mbit/s
Testing upload speed......................................................................................................
Upload: 8.39 Mbit/s

 

So is my router just confused?

 

BT Wholesale shows:

 

snr2.PNG

 

Feel free to move this to the routers section if this isn't the right place for it.

3 REPLIES 3
Baldrick1
Seasoned Hero
Posts: 5,992
Thanks: 2,649
Fixes: 177
Registered: ‎30-06-2016

Re: Target SNR changes

@SteveA 

It’s probably the way the power has come back on. Try switching the hub off using the switch on the back, not the mains. Leave it a couple of minutes then switch it back on.

SteveA
Community Veteran
Posts: 1,785
Thanks: 98
Fixes: 3
Registered: ‎17-06-2007

Re: Target SNR changes

Actually I think the router is partially telling the truth.

 

BTWholesale now shows.

snr3.PNG

Which matches what the router is telling me. So the current connect speeds on the router match what BT are seeing - but the router is still showing slower max speeds.

RealAleMadrid
Seasoned Champion
Posts: 1,382
Thanks: 616
Fixes: 30
Registered: ‎07-07-2009

Re: Target SNR changes

@SteveA  This is typical behaviour after a power cut, the modem/router comes back on with a target SNRM of 3dB and if it syncs up before other modems on the cabinet it can be at a higher speed than expected, then all the other lines get going and create crosstalk so reducing the observed SNRM below the target value. The sync speed is perfectly correct as the BT test shows. Whether the speed stays high depends on the modem continuing to hold sync at the reduced margin. My line with a Huawei HG612 3B modem can only sync at the full 79.99 Mbps after an area power cut with an SNRM of around 1.7dB but it holds on well with next to no errors, currently at over 36 days and counting.😊

Edit. I think this behaviour totally confuses the modem calculating the max attainable rate, it's pretty meaningless anyway nothing to do with actual speeds.