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SNR reduction resulting in sync speed increase

randpwar
Grafter
Posts: 1,308
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Registered: 01-08-2007

SNR reduction resulting in sync speed increase

I realise this sounds like a nice 'problem' to have but I'm not greatly techy and don’t tend to check these things regularly but noticed that my router sync speed has increased from 5440 to 6785. The previous rock solid 5440 rate gave me a profile of 4500 and actual speed of about 4250 for the past 3 or 4 months since I updated all my equipment. According to a table of actual throughput against sync speed my profile should increase to 5500 with an appropriate increase in throughput, assuming the router can hold this new sync rate for a week or so. Noise margin reduced from 9.3 to 6
I’m presuming that the SNR reduction is responsible for the sync rate increase but what would cause this (seemingly) sudden reduction in line noise?   
14 REPLIES
Community Veteran
Posts: 4,729
Registered: 04-04-2007

Re: SNR reduction resulting in sync speed increase

Quote from: randpwar
I’m presuming that the SNR reduction is responsible for the sync rate increase

Its the other way round, the increased sync means that the SNR has fallen.
6dB is the target for MaxADSL, all that has happen is that your new router has found the best sync speed it can get with a 6dB SNR.
randpwar
Grafter
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Registered: 01-08-2007

Re: SNR reduction resulting in sync speed increase

Thanks Chilly  Smiley
It was the time period involved that I found surprising; would it typically take 3 to 4 months to find the optimum sync speed?  Undecided
198kHz
Seasoned Pro
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Registered: 30-07-2008

Re: SNR reduction resulting in sync speed increase

I've had the same experience. Until a month or so ago, my Target SNR Margin was 9dB. I'd been making various improvements in wiring and filtering, and achieved good stability, but it was a couple of months before the DSLAM dropped the target to its present 6dB.  Smiley
Not young enough to know everything
randpwar
Grafter
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Registered: 01-08-2007

Re: SNR reduction resulting in sync speed increase

My IP Profile and PN profile have been increased accordingly to 5500 but according to the Namesco speedtester and BT speedtester (results below) this change has not been reflected in my throughput speed. Will I need to re-boot the router or should the increase in speed be automatic?
Test1 comprises of Best Effort Test:  -provides background information.
    Your DSL connection rate: 6752 kbps(DOWN-STREAM),  448 kbps(UP-STREAM)
    IP profile for your line is - 5500 kbps
    Actual IP throughput achieved during the test was - 2407 kbps
awkelly
Dabbler
Posts: 17
Registered: 06-04-2007

Re: SNR reduction resulting in sync speed increase

A quick disconnect and reconnect (without powering off you equipment) should do the trick...
randpwar
Grafter
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Registered: 01-08-2007

Re: SNR reduction resulting in sync speed increase

Thank you Adam, it worked perfectly; throughput now 5250.    Grin Cheesy Grin

Time for bed
randpwar
Grafter
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Registered: 01-08-2007

Re: SNR reduction resulting in sync speed increase

Things have slipped a little but still good. I notice that Upstream is down to 384kbps, I‘ve never known a router sync at anything other than 448? Is this a symptom of a problem?
ADSL Link                 Downstream Upstream
Connection Speed 6080 kbps 384 kbps
Line Attenuation 47.0 db 25.5 db
Noise Margin 7.1 db 6.0 db
198kHz
Seasoned Pro
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Re: SNR reduction resulting in sync speed increase

Your upstream margin seems rather low - is that a typical reading on your line?
Not young enough to know everything
randpwar
Grafter
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Registered: 01-08-2007

Re: SNR reduction resulting in sync speed increase

As far as I know the router’s always synced at 448 until recently but I have noticed that the actual upstream given via varying speedtesters always gives the figure at about 300. All appears to be okay, profile of 5000 with Namesco speedtester giving 4900, just a bit of an odd upstream speed
pierre_pierre
Grafter
Posts: 19,757
Registered: 30-07-2007

Re: SNR reduction resulting in sync speed increase

well it does say speed not snc
Connection Speed  6080 kbps  384 kbps
that is about correct if a tad high for a 448 syn  my highest is 382
randpwar
Grafter
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Re: SNR reduction resulting in sync speed increase

Thanks pierre_pierre, that's put my mind at ease. As I say, all appears well, just looked odd
198kHz
Seasoned Pro
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Re: SNR reduction resulting in sync speed increase

It may say 'Connection Speed' but router stats always give sync speed.
If the Down sync is 6080, the Up sync should be 448, unless there's a problem somewhere. That's why I questioned the Up SNR Margin - 6.0 seems very odd.
Not young enough to know everything
randpwar
Grafter
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Re: SNR reduction resulting in sync speed increase

A power cut has made the router re-sync at 7328 downstream and back to 448 up; SNR down to 3.2. I’ve no idea why it should have dropped to 384, seems the cut may have done me a favour! or maybe a reboot might have achieved the same. I think I’m right in saying that if the router holds this speed for a week or so then my profile will increase to 6000
198kHz
Seasoned Pro
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Registered: 30-07-2008

Re: SNR reduction resulting in sync speed increase

Probably somewhat less than a week - but yes your profile should be 6000 soon if that sync is maintained.
Not young enough to know everything