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Author Topic: Effects of different ADSL Filters  (Read 11360 times)

Pfrog

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Re: Effects of different ADSL Filters
« Reply #15 on: March 06, 2009, 10:05:25 AM »

Hi HP

Point taken about SRA but surely that is more to do with the adaptive sync speed and not how bitswapping as such is utilised?  I find it hard to understand a standard where a particularly bad burst of noise could permanently remove a great swathe of tones from ever being used - or at least until the router is rebooted? 

Pf
« Last Edit: March 06, 2009, 10:10:05 AM by Pfrog »
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jeffbb

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Re: Effects of different ADSL Filters
« Reply #16 on: March 06, 2009, 02:22:09 PM »

HI
I wonder ? is this logical ?
lets assume that successful bit swapping has taken place (no loss of synch) because of noise and in that process bins X,Y,Z were marked as unusable .Then the bits that were in bins X,Y,Z are now distributed to other bins . So even though the bins may become usable again they will NOT be used until they are required . So until some noise in other channels force bits swapping to populate bins  X,Y,Z (this may not  happen if there is enough SNR in currently populated bins ) the bins will remain empty. If on the other hand you reboot or swap routers then A brand new bin allocation is created .Populating all available bins optimising  SNR. 

Regards Jeff
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Pfrog

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Re: Effects of different ADSL Filters
« Reply #17 on: March 06, 2009, 02:55:13 PM »

Hi Jeff

Sounds perfectly feasible - you may well be right.  However to try and remove the DSL-2740b out of the equation as being the "problem", I have this morning replaced it with a Zyxel P660r-D1 (in half-bridge mode into a WRT54GL).  I am monitoring the Bit / Tone Allocation on OrbMT and will compare the screeeshots tomorrow morning after a night time of noise and will see if the higher tones reappear!  If they don't, the DSL-2740b will be restored......

Regards

Pf
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Pfrog

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Re: Effects of different ADSL Filters
« Reply #18 on: March 07, 2009, 10:20:37 AM »

Well, they always say that practical testing is better than reading / trying to understand the theory!

The Zyxel router has behaved in exactly the same way as the DLink.  The higher tones have not been reallocated this morning and the daytime trace shows the same much reduced higher tones as the DLink......  I assume that if I were to reboot the Zyxel the higher tones whould reappear. 

I have learnt something at least!
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jeffbb

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Re: Effects of different ADSL Filters
« Reply #19 on: March 07, 2009, 11:04:35 AM »

HI

So there is no problem  ;D

Yes I reckon that if you reboot then they would reappear .Not necessarily exactly the same .It would depend on how the bits are allocated .

Regards Jeff
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philip_l

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Re: Effects of different ADSL Filters
« Reply #20 on: May 20, 2009, 07:26:45 PM »

Hi

The action of tones disappearing is definately bitswapping in action, this will often effect tones towards the end of the received range as these typically are the ones hardest to hear, but chunks can disappear from anywhere due to random noise that comes and goes.

Once they are completely bitswapped they will be de-activated and not used again until a resync, where the cycle continues.  This bitswapping and disabling of the tones also results in a gradual lowering of reported SNR margin until a resync.

Regards

Phil

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