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Author Topic: Signal attenuation Vs. Line attenuation  (Read 9917 times)

kezzaman

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Signal attenuation Vs. Line attenuation
« on: June 09, 2012, 02:56:11 PM »

Hello,

Should i be concerned that my signal attenuation isnt equal to my line attenuation?  :-\
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roseway

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Re: Signal attenuation Vs. Line attenuation
« Reply #1 on: June 09, 2012, 03:31:23 PM »

As I understand it, line attenuation is a characteristic of the line, measured under specified conditions, but signal attenuation is the actual attenuation measured by the router, under the conditions existing at the time of measurement. So the former should be fixed, but the latter can vary as signal conditions change.
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  Eric

kezzaman

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Re: Signal attenuation Vs. Line attenuation
« Reply #2 on: June 09, 2012, 03:53:27 PM »

As I understand it, line attenuation is a characteristic of the line, measured under specified conditions, but signal attenuation is the actual attenuation measured by the router, under the conditions existing at the time of measurement. So the former should be fixed, but the latter can vary as signal conditions change.

I dont understand ur answer  ???
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roseway

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Re: Signal attenuation Vs. Line attenuation
« Reply #3 on: June 09, 2012, 04:32:55 PM »

Sorry, I can't think of a simpler way of putting it. Perhaps someone else can do better. But the answer to the question you asked at the top is no, you needn't be concerned.
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  Eric

4candles

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Re: Signal attenuation Vs. Line attenuation
« Reply #4 on: June 09, 2012, 04:54:52 PM »

Hello,

Should i be concerned that my signal attenuation isnt equal to my line attenuation?  :-\

I assume by 'signal attenuation' you mean the attenuation figure in your router stats.

What is the source of your 'line attenuation', and what are the two figures?
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kezzaman

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Re: Signal attenuation Vs. Line attenuation
« Reply #5 on: June 09, 2012, 05:26:59 PM »

Hello,

Should i be concerned that my signal attenuation isnt equal to my line attenuation?  :-\

I assume by 'signal attenuation' you mean the attenuation figure in your router stats.

What is the source of your 'line attenuation', and what are the two figures?

My line attenuation which is the attenuation on my router stats is 6.5, my signal attenuation which im getting from a telnet command is 7.6. This is on my upstream.

My downstream values are equal 14.5 14.5.
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4candles

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Re: Signal attenuation Vs. Line attenuation
« Reply #6 on: June 09, 2012, 05:41:31 PM »

Ah, thanks for the clarification.

In ye olden tymes, pre BB, line attenuation, although not normally measured or recorded on subscriber exchange lines, would be from 0 to about 3dB, at 800Hz or 1600Hz.

Obviously though, you're referring to broadband, and I'd agree with Roseway - nothing to be concerned about. Just a little quirk of the router.
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Black Sheep

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Re: Signal attenuation Vs. Line attenuation
« Reply #7 on: June 09, 2012, 05:56:06 PM »

As I understand it, line attenuation is a characteristic of the line, measured under specified conditions, but signal attenuation is the actual attenuation measured by the router, under the conditions existing at the time of measurement. So the former should be fixed, but the latter can vary as signal conditions change.

Eric (Roseway) is 100% correct. The individual buckets/bins at each 4.3Khz intervals, will have varying degrees of Insertion Loss/SNR, dependant on conditions at that time. thus, giving varying 'Signal Attenuation' readings.

Line attenuation is taken at just one reading (300Khz), rather than over the whole array of bins/buckets that 'Signal attenuation' is taken from. IE- 256 Bins for ADSL1 ..... 512 Bins for ADSL2+ etc etc.

As already mooted, there is no need for concern whatsoever that the 2 readings are different.  :)
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snadge

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Re: Signal attenuation Vs. Line attenuation
« Reply #8 on: June 12, 2012, 01:00:57 AM »

As I understand it, line attenuation is a characteristic of the line, measured under specified conditions, but signal attenuation is the actual attenuation measured by the router, under the conditions existing at the time of measurement. So the former should be fixed, but the latter can vary as signal conditions change.

Eric (Roseway) is 100% correct. The individual buckets/bins at each 4.3Khz intervals, will have varying degrees of Insertion Loss/SNR, dependant on conditions at that time. thus, giving varying 'Signal Attenuation' readings.

Line attenuation is taken at just one reading (300Khz), rather than over the whole array of bins/buckets that 'Signal attenuation' is taken from. IE- 256 Bins for ADSL1 ..... 512 Bins for ADSL2+ etc etc.

As already mooted, there is no need for concern whatsoever that the 2 readings are different.  :)

this seems to be confusing me even further lol.. (which isnt hard)

... on mine DMT Tool says @ 300kHz = 21db - but my Line Attenuation figure in the router is 26-27db (depending on router I use) - isn't the figure 'Line Attenuation' qouted in the router an 'average' of the Line Attenuation across all the tones? (rather than the LA at 300kHz.?) or is it something to do with ADSL2 having 512 tones as to why the LA is slightly higher?

with regards to the differences between the two, an easy way to explain for the OP (I think) is think of the Line Attenuation figure a representation of your LINE CONDITION, and the Signal Attenuation a representation of the SIGNAL CONDITION over the LINE :) - as your line doesnt change then niether should your LINE ATTENUATION , but your signal does vary and therefore so should the SIGNAL ATTENUATION figure ...sorry if I got that totally wrong, but thats my understanding of it
« Last Edit: June 12, 2012, 01:16:10 AM by snadge »
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Black Sheep

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Re: Signal attenuation Vs. Line attenuation
« Reply #9 on: June 12, 2012, 06:43:19 AM »

You are probably right when it comes to 'router reporting' of the line attenuation. But, we have a recorded account on a system called 'SEAM', that logs each and every individual cable to Cab, and the figures are taken at precise frequencies. 1.6Khz and 300Khz being the two we most relate to.

 
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c6em

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Re: Signal attenuation Vs. Line attenuation
« Reply #10 on: June 12, 2012, 08:15:13 AM »


Correct.

The router reported "line attenuation" is a mathematically derived average of all the individual attenuations at each frequency bin/tone up the scale.  It is important to note that this average is made up of those frequencies that are actually used and NOT those available to use. 
So if some frequencies/tones are not used due to noise then this will affect the attenuation figure.  This is why the same line on ADSL2+ will have a higher attenuation as the router is now using more frequencies up the range on ADSL2+ compared to the attenuation reported by the same router on ADSLmax.

The 300KHZ attenuation figure is the raw actual measured line attenuation at that sole particular frequency of 300 KHz. The DMT tool reports this figure.

My figures are:
DMT reported attenuation at 300Khz is 29dB and is always this figure at all times and back in years.

Router reported line attenuation either 35.5 or 36 depending on the time of the last reboot - which affects the tones used as if it's done in the evening there will be fewer used due to general noise so I get a reported attenuation of 35.5.  If the re-boot is done in the morning the answer is 36.0.
(On Adlsmax it was 34 from What I can recall).

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roseway

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Re: Signal attenuation Vs. Line attenuation
« Reply #11 on: June 12, 2012, 10:33:21 AM »

This still doesn't make clear the distinction between line attenuation and signal attentuation. There's an article here which attempts to explain it. In short, line attenuation is reported by the DSLAM/MSAN, and is calculated using a pre-defined set of signal parameters; signal attenuation is reported by the modem/router, and is calculated using the actual existing signal conditions.

PS This is separate from the fixed-frequency values referred to by Black Sheep. The 300 kHz value is reported by a few routers, and I gather that it's a standard measurement made by OR. This value is completely independent of signal conditions, and doesn't take into account higher frequency losses, which is why it's generally lower than the normal attenuation value reported by the router.
« Last Edit: June 12, 2012, 11:49:56 AM by roseway »
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  Eric

kezzaman

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Re: Signal attenuation Vs. Line attenuation
« Reply #12 on: June 12, 2012, 10:33:32 AM »

Disabling bitswap decreases my signal attenuation on the upstream, does anybody have an explanation for that?
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kezzaman

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Re: Signal attenuation Vs. Line attenuation
« Reply #13 on: June 12, 2012, 11:31:49 AM »

This still doesn't make clear the distinction between line attenuation and signal attentuation. There's an article here which attempts to explain it. In short, line attenuation is reported by the DSLAM/MSAN, and is calculated using a pre-defined set of signal parameters; signal attenuation is reported by the modem/router, and is calculated using the actual existing signal conditions.

Aftr reading the link you posted, do you think its possible that the MSAN on my line thinks my modem is closer than it actually is and its not "shouting" loud enough for my modem to hear it properly. Or on the other hand could my modem think the MSAN is further away than it actually is and my modem is shouting to loud and its distorting my broadband?
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guest

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Re: Signal attenuation Vs. Line attenuation
« Reply #14 on: June 12, 2012, 12:31:56 PM »

Worth bearing in mind that Be/O2 (for one) don't use a 300kHz test tone.

They (from memory) use tones 175-178 so frequency is from about 750kHz to 770kHz. Using multiple tones apparently improves reliability of results. Personally I think its just Be testing on the cheap as support don't have any way of monitoring live line conditions.
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