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Standard User christopherpovey
(regular) Tue 18-Jan-11 17:27:04
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Question About SNR Margin...


[link to this post]
 
Before I signed up to BT Broadband in November I did the speed test on their website and got back 8Meg as my maximum. However my router was set to GMT at the time.

Upon connection to BT I changed my Vigor 2800 router to auto and it connected as ADSL2+ at 10Meg. I knew this was subject to testing over 10 day period so I waited. Anyway I am now connected to the exchange at approx. 15Meg. However my router is reporting SNR Margin of 1.5 and Loop Att of 24.

I have read that a SNR Margin value of less than 6db would result in drop outs. However my router shows that the current connection has been alive for 151 hours! So this clearly is not happening.

Are there any other values I can look at to see if the SNR Margin is an issue? Is there anything I can do about it?

Thanks.

Christopher Povey
Standard User MHC
(legend) Tue 18-Jan-11 18:15:32
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Re: Question About SNR Margin...


[re: christopherpovey] [link to this post]
 
Not true.

The BT Business 2Wire 2700HGV will sync at 3 dB and then with background noise variations that can vary and it will hold sync down to 0dB and sometimes below (I have seen -0.7dB).

Get RouterStats Liute and if you can get it running with teh Vigor do a plot for 24 hours and you will see how SNR varies - if you want, start with a resync and 8:00 AM and go from there.

http://i2.photobucket.com/albums/y31/Polchraine/TBB/... Shows 0.5 dB and

http://i2.photobucket.com/albums/y31/Polchraine/TBB/... the variation from 4.2 dB down to 0.5dB





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M H C


taurus excreta cerebrum vincit
Standard User RobertoS
(sensei) Tue 18-Jan-11 18:27:18
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Re: Question About SNR Margin...


[re: christopherpovey] [link to this post]
 
smile
Don't worry. Yet tongue!

The value of 6dB is a margin, as you realise, that is established at the time you connect, to allow for the fact that the actual noise varies 24/7. So (in simplified terms) it means that actual noise can rise by 6dB without the connection being lost.

Assuming yours was 6dB at connection time, (which isn't in fact certain), then the noise has gone up by 4.5dB so the margin has fallen by 1.5dB. Which is fine!

What you have read is that if the sync-time margin is less than 6dB that can result in dropouts. Which in your case, with the above figures, would have happened if it hadn't been 6dB then. 6dB is sufficient to keep nearly all lines connected because very few vary over 24 hours by that much.

I have a fuller and better explanation on this page.

The way the latest BT DLM works it seems on good lines it can set the sync-time margin to 3dB. I suspect that is what yours is at, and noise has risen by 1.5dB.

As long as you aren't getting dropouts, and the error rates are not very high, then relax and enjoy the speed smile.

My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost. Internet connection - O2 Standard.


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Standard User XRaySpeX
(knowledge is power) Tue 18-Jan-11 19:42:07
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Re: Question About SNR Margin...


[re: christopherpovey] [link to this post]
 
In reply to a post by christopherpovey:
Before I signed up to BT Broadband in November I did the speed test on their website and got back 8Meg as my maximum. However my router was set to GMT at the time.
Actually you didn't do a speedtest as such, but a "Check what speed I could get if I went with BT" which is solely an estimate based only on some fallible data that BT holds on your line. It does not test your actual speed at the time and so your router settings do not come into it.

Most ISPs such speed/availability checks tend to highly underestimate your line in order to cover their ... eh ... risk.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU BB => 2010: Orange 16 Meg LLU BB
Standard User christopherpovey
(regular) Tue 18-Jan-11 21:48:10
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Re: Question About SNR Margin...


[re: MHC] [link to this post]
 
Thanks for the responses.

I see now! smile

Actually my router is currently sitting at SNR Margin of 6db, but the connection has reset recently as it shows an up time of only 4 hours now! The Upload and Download speed are as before.

Christopher Povey
Standard User christopherpovey
(regular) Sat 22-Jan-11 10:33:51
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Re: Question About SNR Margin...


[re: christopherpovey] [link to this post]
 
I was surfing last night when it dropped out. Fired up the router software to see it handshaking. It reconnected at 7,102,900 down, with a SNR Margin of 16.0! Power cycled the router this morning and its the same. Not happy! frown

Christopher Povey
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