SNR for VDSL

daz87uk

daz87uk

daz87uk

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Joined
30 Nov 2008
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930
Location
Newquay
Hi, I recently bought a DSL-N66u. I have been trying to tweak the settings for the modem so it stabilizes a bit better but I am find it difficult to find any information the the different vdsl modem settings that should be touched without screwing everything up basically.

I get a line sync:

Down=79968kbps
up = 19999kbps
Snr down =6.2dB
Snr up =16dB
attenuation down = 6dB
attenuation up = 1.4dB
Power down -3.7dbm
Power up -3.6dbm

over night the line has been dropping a few times, and generally Im getting a few crc errors. Not a huge amount but at least 1 every hour or two.

I have a few Settings I can adjust but Im not sure which ones are ment to be touched in accordance with DSLAM.

atm:

stability adjustment (VDSL) [Disabled]
tx Power (VDSL) [Disabled]
Rx AGC GAIN Adjustment (VDSL) [Disabled]
UPBO - Upstream Power Back Off (VDSL) [Auto]
seamless Rate Adaptation [Enabled]
Bitswap [Enabled]
Share PVC [Disabled]

I had a quick browse on the internets and found that UPBO should be on to stop interference from other lines. the router has this set to [Auto] but when I set it to Enabled the SNR down goes from 6.2 to 7.8/7.9 it fluctuates a little and SNR up is now 15.5 up to 15.8

Does this sound correct is there any other settings I should be making. :confused: I'm not sure if SNR is best lower or higher seems to be a bit conflicting information on the web

cheers.
 
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I wouldn't panic about 1 or 2 CRC errors an hour, it's not a huge issue. Are you sure it's not just DLM running on the line? Is ti stable throughout the day?
 
I think you might be right, it was over night and the last disconnection was around 10.30am. Seems ok in the day. What about snr? It's fluctuacting slightly atm it's gone up to 8.3db since Turing on the upbo

Cheers
 
ok so I've turned upbo off and now I get this...

SNR DOWN = 6dB
SNR Up = 32dB???

Line Attenuation Down 9dB
Line Attenuation Up 1.6dB

Power Down is now 9.4dbm
Power Up is now 9.6dbm


good or bad? I don't fully understand the readings so any help appreciated :p
 
High SNR is good (sort of) as you won't be able to tune it for more than 80/20 and your already there the only thing you could do with it is set the target higher so as to make the line more stable at a possible loss of sync speed.

The upload SNR will likely be really high as the newer VDSL profiles are capable of upto ~130Mbit sync (not 100% sure which BT are actually using but even 17a would give a fair amount more than 20Mbit upload potential) if your fairly near the cabinet so with them capped at 20Mbit theres a ton of margin.

Line attenuation you want as low as possible - yours look fairly decent so if your having disconnects its probably not a line issue but either DLM doing its job or some external interference causing random spikes.


EDIT: To be a bit clearer the higher SNR numbers you get the higher line speed you can potentially get - but as you let the line sync at higher rates the reported SNR will drop - high SNR numbers aren't a problem other than your not using the line to its full capabilities - when the numbers start dropping below ~6db with current tech you can start to get stability issues - 6 itself isn't a problem as that is the target SNR often used to train the line to.
 
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:eek:Well I haven't been booted since DSLAM corrected my last fiddle with setting the target higher. it dropped the line speed down to 60 then 54:eek:.

its now back up and running with most of the tweaking disabled as this seems to be the cause of me being booted...

atm I was just looking at the upbo setting as I seem to get slight variations from auto to on / off.

Line attentuation has gone from 6 to 9 down and 1.4 to 1.6 up. turning upbo off but the snr is currently 5.9 down and 31.1up. So I wasnt entirely sure if I was better off leaving it off or on or on auto...

will have to wait I guess but takes so damn long to confirm if the setting is correct...
 
ok its just in the router I have the adjustments for (adsl) and bellow it (VDSL) but your saying this will not work. as I wasnt 100% given the router says VDSL snr adjustment...

asus.JPG
 
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Last February my FTTC is maximum rate of 113136k / 38700 with snr of 15.1 / 23.2
Current now my FTTC is maximum rate of 93260k / 33562k with snr of 9.7 / 15.0

However sync rate is not affect at the moment still getting 79999k / 19999k

Question are what is the maximum rate if the downstream snr went down to around 6? Will snr carry on reduced down around 3 or will stop at 6?

P.S. I guess could be around 82000k with snr of 6 something like that.
 
currently the maxium rate is 104k and 50k up. I think at first sync it was a tad lower. I will have to wait a few days to see what the DSLAM makes of this new change as my sync is still 79968 atm and 19999 up.

I'm also not sure what difference the dbm makes as its gone from -3.7 to both bring + 9.4. I read somewhere that 0 / + was best but not 100%
 
Rroff said:
EDIT: To be a bit clearer the higher SNR numbers you get the higher line speed you can potentially get - but as you let the line sync at higher rates the reported SNR will drop - high SNR numbers aren't a problem other than your not using the line to its full capabilities - when the numbers start dropping below ~6db with current tech you can start to get stability issues - 6 itself isn't a problem as that is the target SNR often used to train the line to.
Click to expand...

thanks I thought it was something like that :)
 
cant wait for my fibre connection, goes live on the 14th oct :D and im less than 1k from my exchange :D
and i have the dsl_ac68u to :D
 
I can see two green boxes 300ft line of sight. :), they are unmarked though so not 100%. Apparently the exchange is also 700m away not that matters ofc :).
 
Deffinetly enable upbo... Down tunes upstream power and stablises the line better. Result 2mb faster upload. Plus apparently throwing max power down the line ruins everyone elses internet and upsets bt :D
 
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