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Can plusnet lock your SNR?

mattstead
Grafter
Posts: 41
Registered: 17-12-2010

Can plusnet lock your SNR?

My default SNR seems to be at the usual 6db (or at least it tries to be),  This seems suprising considering how far I am from the exchange....one of the many BT engineers who have been out said he expected me to be running at 12db. So is it possible for plusnet to set my target SNR at a higher amount? I only ask this as my SNR is still all over the place (after about 8 visits, a new cable to the road, and a lift and shift at the exchange), and I was thinking that if my SNR started higher then when it drops dramatically it is less likely to drop to an unacceptable level.
I know that raising the SNR will reduce my speed, but due to the instability my IP profile has been at 135K for the 3 months since joining plusnet, so the added stability might get my speed up...if it's possible to lock the SNR.?
16 REPLIES
Community Veteran
Posts: 6,735
Thanks: 12
Registered: 02-02-2008

Re: Can plusnet lock your SNR?

Almost any ISP can set a target SNR which is used at sync time.
The default on most is 6dB but it can be higher, e.g. 9 or 12dB.
DLM can also change it, not sure how that would interact though.
Obviouslt the actual SNR changes during a "session" as conditions change.
mattstead
Grafter
Posts: 41
Registered: 17-12-2010

Re: Can plusnet lock your SNR?

Thats's promising then..I expect the SNR to change throughout a session, I just hope that if it starts from a much higher level then it might just be stable.
knowdice
Grafter
Posts: 328
Registered: 25-04-2008

Re: Can plusnet lock your SNR?

Higher SNR will be more stable especially on a long line, this will of course be at the expense of speed.
i.e. a 6dB higher SNR will half your sync speed  Embarrassed
itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: Can plusnet lock your SNR?

Quote from: knowdice
i.e. a 6dB higher SNR will half your sync speed  Embarrassed

Why do you know it will half the speed? You are not getting confused with power when -3dB drop the power by half.
knowdice
Grafter
Posts: 328
Registered: 25-04-2008

Re: Can plusnet lock your SNR?

3dB for power.
6dB for voltage ratio.
itsme
Grafter
Posts: 5,924
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Registered: 07-04-2007

Re: Can plusnet lock your SNR?

Yes but it does not apply to broadband speed.
knowdice
Grafter
Posts: 328
Registered: 25-04-2008

Re: Can plusnet lock your SNR?

Pretty sure it does.
Moderator
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Re: Can plusnet lock your SNR?

Quote from: http
Each line needs a specific amount of SNR to run at a given speed. Very roughly its often said that 1dB of SNR equates to 450kbps of speed, but other factors such as attenuation and output power need be bourne in mind and some lines may only see around 1Mb per 3dB.

Customer and Forum Moderator.

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itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: Can plusnet lock your SNR?

You are aware that what being discussed here is a SNR margin. Not the actual SNR.
knowdice
Grafter
Posts: 328
Registered: 25-04-2008

Re: Can plusnet lock your SNR?

What I'm saying is whilst there are a lot of factors that determine the actual speed your router actually syncs at.
If for example you are on a long line and with a target SNR of 6dB and you get say 2mbs download sync, if you change the target SNR to 12dB then the sync speed will drop to 1mbs.
dick:quote
Community Veteran
Posts: 6,735
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Registered: 02-02-2008

Re: Can plusnet lock your SNR?

Quote from: knowdice
If for example you are on a long line and with a target SNR of 6dB and you get say 2mbs download sync, if you change the target SNR to 12dB then the sync speed will drop to 1mbs.

That's not inconsistent with the Kitz observation.  Wink
On shorter lines at higher speeds you will definitely NOT get a halving of connection speed by such a change.
Best thing is to try it and see what the effects are.  Cool
Community Veteran
Posts: 5,636
Thanks: 752
Fixes: 1
Registered: 23-09-2010

Re: Can plusnet lock your SNR?

You could also just reconnect when your snr is low, which would basically have the same end result.
wisty
Pro
Posts: 456
Thanks: 59
Fixes: 4
Registered: 30-07-2007

Re: Can plusnet lock your SNR?

If you use a Netgear 834 with the DGTeam firmware you can ask the router to negotiate a higher (or lower) SNR, and the change survives a router restart.
gyre
Grafter
Posts: 271
Registered: 19-11-2007

Re: Can plusnet lock your SNR?

I've had some wierd effects with the DLM and changing target SNR margins with the broadcom chipset in the past.
Starts off as expected, but then it seems on the next resync to need a bit more reduction and then a bit more just to keep the same margin.
I could start off at 80% to get to the target SNR margin I wanted, but then a few resyncs later I'm on 40% to get the same effect.  Almost as if the BT DLM mechanism is fighting me.
-- gyre --