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Author Topic: 'Output Power' - chicken or egg?  (Read 7206 times)

b4dger

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'Output Power' - chicken or egg?
« on: August 03, 2009, 07:34:55 PM »

Hi all,
Back with the latest saga in my changing line!  ???

After going for months and months (December 2008) with good results for my line (Attenuation 51) things have taken a turn for the worse lately  :no: 

After lots of error/noise bursts my line went from syncing around 5500 > 3500.
Target SNR in Dec. was 6 - now 12db.

In the last couple of days things might be on the up!
When the line was syncing around 3500 which is low for a 12db Target SNR line of my length I noticed the router (Speedtouch 585v6) reported a lower than normal Output Power.


I turn on all my kit in the morning.
When I see 18.5 dBm Output Power(down) I know it's going to be a bumpy day!
It has been like that since a stormy day a week ago Friday.
Yesterday it returned to 19.5 dBm and sync'd at 39xx  and today it's still 19.5 and synced at 4096 :)

Chicken or Egg? So is my Output Power higher due to my line being healthier OR is my line healthier as the Output Power has risen?


Any ideas on what's been happening?

For those that haven't seen my previous posts - my wiring is all optimised and I have a swapped my trusty 585 for another from my collection just in case.

Kitz has mentioned Output Power in a couple of other interesting posts here but I'm looking for more info if anyone can help.

Thanks in advance as always.

(NB. I asked my ISP Freeola/Enta for help the other week when I saw my Target SNR being trashed but didn't really get anywhere. It was left with possible problems caused by tree branches.)




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coolsnakeman

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Re: 'Output Power' - chicken or egg?
« Reply #1 on: August 03, 2009, 07:45:12 PM »

Are you on overhead cabling cause if you get bad weather with overhead cabling in place the line tends to flap causing your speed to decrease to keep the service stable. If your cable is underground then that is that out the window lol. Usually tree branches do tend to cause an issue especially if they are hitting off your phone line causing it to flap. You could maybe speak with your local counsellor and see if they would be so kind to trim the branches down for you.
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b4dger

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Re: 'Output Power' - chicken or egg?
« Reply #2 on: August 03, 2009, 07:47:56 PM »

Hi, yes I do have overhead wiring - hence the tree comment  ;)

I'm not convinced trees are changing things - just put that in for a fuller record...


I'm really after some more info on the changing Output Power reported.
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kitz

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Re: 'Output Power' - chicken or egg?
« Reply #3 on: August 03, 2009, 08:27:54 PM »

I'm not certain on this as Ive never been able to find anything that actually defines the PSD masks and their limitations.
All I know is that theres 4 PSD (Power Spectral Density) Masks that are applied in the UK and these are dependant on line length. (Extra short, short, medium & long).

Your output power during the sync up phase will be defined (amongst other things) dependant upon this mask, and also your SNR.  
If your SNR (or it could be SNRM?) exceeds 'x'dB, the the output power will be reduced according to prevent crosstalk.
Most rate adaptive lines syncing a maximum capability will have an output power in the region of 18-19dBm.

If after sync-up, a line starts to struggle, and SNR dips too low, then the DSLAM/router can increase the power output by say up to 1dBm.  Conversely if the line improves and SNR starts to rise above the 'x'dB, then power output will be decreased.

General observation would be that if your line has >19dBm output power then its reaching its limits.
If your line has <17.5dBm then a resync may be beneficial.

>> So is my Output Power higher due to my line being healthier OR is my line healthier as the Output Power has risen?

Chicken and egg indeed.

Youre able to sync higher because the output power has increased (Signal Strength)... but in all possibility it will have increased because of some point its struggled.
If your SNR goes above that x level again, then theres a chance that ouput power will decrease.

Hard to explain but think of the output power as something that may vary depending upon your line conditions... or rather as a result of your SNR fluctuations.
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b4dger

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Re: 'Output Power' - chicken or egg?
« Reply #4 on: August 03, 2009, 08:40:52 PM »

Hi kitz,
NB. This was an earlier post of yours re. Output Power

A resync certainly wasn't helping my line - so I'm thinking Output Power is yet another one of those 'things' that your can't control and it's all up to the rules of the DSLAM.

FWIW I don't seem to see my Output Power change throughout the day - even if my noise margin should improve/reduce.  Do you see yours change? I wonder if some routers cope with this element better than others?



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kitz

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Re: 'Output Power' - chicken or egg?
« Reply #5 on: August 03, 2009, 09:23:14 PM »

I pressume you mean this

Quote
>> output power  . The most I have seen is 19.8 db  downstream

I have since seen a line running at 20dB, but only the once... most lines running at full power still seem to be around the 19.5 -19.8 mark.

By that I meant when it was running maximum/full pelt after having been 'boosted'.

My own line is normally about 18dBm..  but say after a bad period when the SNRM was dropping it went up to 19dB.

Other info from that post - Id orginally stated there was 3 PSDs, which there was,  but Ive since found out that the UK more recently added another one for very short lines.
Ive also since found out that the theoretical max output power sent from the dslam is 20.4dBm..  incidentally iirc VDSL/FTTC may be 15dB.

Theres not much plain english info about output power and the PSDs...  the main focus is not letting power output get too high.. and that will be defined within the PSD.

>> FWIW I don't seem to see my Output Power change throughout the day - even if my noise margin should improve/reduce.

I dont think its dynamic as with SNR, but more based on what has occurred.. Im not even sure exactly what can trigger it.
Mine varies between 18-19dBm - not on a per second basis.. but more over days/weeks.  It could perhaps more be controlled like a 'Target SNR'?  Aside from that if signal strength does get too strong (high SNRM) then it should kick in... sorry dont know much more.

There is some more info in the ANFP Specification, if any one wants to have a read and perhaps translate it into plain english and how it would affect our lines. ???
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kitz

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Re: 'Output Power' - chicken or egg?
« Reply #6 on: August 03, 2009, 09:29:46 PM »

PS...  just as I was writing the above post I got passed these links

ND1602:2005/08

ND1604:2006/09

If someone has the time to read, digest and see if it provides any more info that may be of use then please do.

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silversurfer44

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Re: 'Output Power' - chicken or egg?
« Reply #7 on: August 04, 2009, 08:20:09 AM »

Very interesting reading this thread. However I feel the output power is a very complicated piece of the puzzle. For quite a while now, months, the output power reported by my Netgear using the DGTeam firmware and Routerstats has varied hour by hour. The sweet spot seems to be 18db when I get the best sync speed. The SN target appears to be 6db but after a couple of hours the speed will drop by approx 1meg, the noise margin will go up and the output power will go down to around 16db.
Yesterday I decreased the SN target, using the Netgear advanced tool, from the usual 6db to 3db or 50%. Upon checking Routerstats I found that immediately the output power was reported as 18.3db, the modem had re-synced (without disconnection) at roughly 1meg faster than before the alteration. Checking again this morning everything is still at the same values as yesterday which is unusual for my line.
Chicken & Egg springs to mind again, does the modem control the output or does the dslam or whatever control it?
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kitz

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Re: 'Output Power' - chicken or egg?
« Reply #8 on: August 04, 2009, 09:59:54 AM »

>> does the modem control the output or does the dslam or whatever control it?

AFAIK both.

Dslam for downstream, router for upstream.
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orainsear

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Re: 'Output Power' - chicken or egg?
« Reply #9 on: August 04, 2009, 06:07:50 PM »

Am still going through all this (and I thought that the aerospace industry was bad for acronym use), but when you've seen the output power changing, have you noticed any changes in the reported attenuation?
« Last Edit: August 04, 2009, 06:11:16 PM by orainsear »
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silversurfer44

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Re: 'Output Power' - chicken or egg?
« Reply #10 on: August 04, 2009, 07:12:08 PM »

Acronyms? You ain't seen nothing yet. In this game there seems to be acronyms for acronyms ???
I did go through a spell where the downstream attenuation did fluctuate between 50db and 48db, but it has been stable at 49db for a while now. AIUI small fluctuations are nominal and to be expected.
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waltergmw

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Re: 'Output Power' - chicken or egg?
« Reply #11 on: August 04, 2009, 08:33:51 PM »

I'm not sure if the following pictures might help or complicate matters. They are all on the same long line with a mere 82 dB downstream attenuation @ 300 kHz.
There is one picture of DMT Tools showing output powers which seem to remain quite constant, possibly because the 585V7 router didn't reboot, and then four pictures of stats from a 2Wire 2700 HGV showing differing powers and a quite different bit loading shape. Perhaps Kitz might coment but I suppose the routers use different algorithms.

Kind regards,
Walter

http://www.scribd.com/doc/18107661/2Wire-DSL-Diags

http://www.scribd.com/doc/18107662/2Wire-Diagnostics

http://www.scribd.com/doc/18107664/2Wire-DSL-Stats

http://www.scribd.com/doc/18107666/2Wire-Training-and-Bit-Loading

http://www.scribd.com/doc/18107667/585V7-13-12-Pic-1
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orainsear

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Re: 'Output Power' - chicken or egg?
« Reply #12 on: August 04, 2009, 09:54:20 PM »

At risk of stating the obvious am I right in thinking that the reported downsteam power is a value that is calculated by the modem rather than the actual value set by the DSLAM?
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b4dger

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Re: 'Output Power' - chicken or egg?
« Reply #13 on: August 05, 2009, 06:15:38 PM »

At risk of stating the obvious am I right in thinking that the reported downsteam power is a value that is calculated by the modem rather than the actual value set by the DSLAM?

I'm not sure you are stating the obvious  ;)
I think it's all at the DSLAM end, but perhaps some routers can manage things better than others?

From my point of view all I see is that if my Speedtouch 585v6 reports 19.5 dBm then things are looking up!
But as I originally said - I don't know if this is because my line has improved - egg/chicken...
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coolsnakeman

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Re: 'Output Power' - chicken or egg?
« Reply #14 on: August 05, 2009, 06:46:05 PM »

I don't know very much about output power so this question might come across a little silly but is this not the same as "gain"? If that is the case then does your SP not have the tools to mess about with this at the DSLAM or send an engineer out to mess about with this cause i have heard of OR engineers increasing the "gain" at the exchange to get BB on long lines.
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