Understanding High Signal Attenuation

[#1]

As an aside to this thread, could someone please explain what "Line Attenuation" and "Signal Attenuation" actually mean in this context, and specifically, why they are different?

Is it just co-incidence that for both the OP and I, our Upstream Line and Signal Attenuations are the same, (2.1 in my case, 15.6 in theirs), but for the Downstream they are different, (4.5 and 4.7 for me, 33.1 and 46.3 for them)?

TIA

[#2]

@Mr_Paul I, like you, would have do an online enquiry to answer the first pat of your question - sorry.

The second bit, and it is only a guess until the OP provides the data I requested, is probably due to the different distances between the properties and the Fibre cabs.

[#3]

@jab1 

Thanks for the reply.

"The second bit, and it is only a guess until the OP provides the data I requested, is probably due to the different distances between the properties and the Fibre cabs."

Yes, I'd realised that the OP being significantly further away from the cabinet than me, (they 1200 metres, me only 50 metres), was the reason they see a higher attenuation figure.

My question though, and hopefully if/when someone comes on to explain the difference between Line and Signal Attenuation this will become clear, is why (for example), I have an Upstream Line and Signal Attenuation of 2.1dB (ie the same), but my Line Attenuation is 4.5dB and the Signal Attenuation is 4.7dB.

Why are Line and Signal not the same?

In the OP's case, the difference is even more noticable: both Upstreams are 15.6, but their Downstreams are14.1 vs 33.1.

Is this in itself a clue to the problem they are having?

[#4]

Why are Line and Signal not the same?

In the OP's case, the difference is even more noticable: both Upstreams are 15.6, but their Downstreams are14.1 vs 33.1.

Is this in itself a clue to the problem they are having?

@Mr_Paul  In answer to the question above, I don't personally think so - I suspect the high d/s SNR is more relevant.

[#5]

Courtesy of Kitz https://kitz.co.uk/adsl/linestats.htm#Signal_v_Line_Attenuation

 ~ What is the difference between Line Attenuation and Signal Attenuation?

Routers that display two sets of attenuation figures are usually reporting the Signal Attenuation and Line Attenuation.   In these cases it can be taken to mean:-

• Line (or Loop) Attenuation is an average of all the tones available for use in the relevant dsl spectrum - regardless of if the tones are in use or not.
  Loop attenuation is calculated during the transceiver training phase of the initialisation process and is an estimation of the line attenuation averaged through all the upstream or downstream subcarriers.
• Signal Attenuation is monitored and reported as an ongoing process and can sometimes be affected by ongoing changes in line conditions. Calculation is performed as the difference between the power transmitted at the far end and the power received at the near end.
  Signal attenuation is based an average of the frequency bins in use during showtime and therefore it is not considered unusual if Signal attenuation is slightly lower than Line attenuation.

[#6]

EDIT - POST DELETED - as @MisterW  had a better answer

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[#7]

So my simple interpretation is that the Line Attenuation is a reference value determined when the line is initialised. Signal Attenuation reflects the present real world situation. The difference gives an indication of varying interference/cross talk that knock out broadband tones or a high impedance cable connection.

Assuming that this is correct, the questions that come to mind are what are the time scales for the two to be updated and is the difference a factor in triggering DLM action, or is that simply determined by error count? There’s obviously a lot of interesting material here for the geeks amongst us.

[#8]

@Baldrick1 I agree, but it is likely to confuse the OP. 😀 Any chance of taking it elsewhere? 😉

[#9]

Hi John,

Apologies for reverting late.

Note that I had a couple of disconnections in sequence yesterday which led to PlusNet resetting some settings -download speed went down to 3.5Mps. I guess that reset leads to some broadband tests which are not aligned with the situation I had earlier.

Now this does not change the NSR and Line Attenuation, but the download speed is better aligned with the max available speed now. That said, it was the same as when the OpenReach engineer came over last time, and then after a few weeks the download speed went back to 7.8Mbps with some times massive drops to 1.5Mps. I would expect to face the same again as I still suspect there is an issue with the overhead cable.

Anyway, first thing first: I am on an FTTC, not ADSL as I wrongly stated previously.

I ran the Quiet Line Test and had no noise on the line.

The BT Broadband Test gave me that:

The BTW Performance Test led to:

And the current Technical Log - Information webpage of the router is:

As pointed out above, it's only up for 20 hours as we had to reset the line yesterday.

[#10]

@itlity 

The results show you're on a FTTP Priority Exchange. Given the speeds shown I would expect OR to be planning FTTP unless you're way out in the sticks and it's unaffordable.

You can check the following sites

https://www.openreach.com/

https://checker.ofcom.org.uk/

Note Ofcam only shows active networks - not those in planning or build.

Brian

[#11]

We are remote, there are about 4 houses over a 2km road stretch -and not on an A or B road, so don't think it would make sense economically to have FTTP.

Having a 13Mbps connection at our place is already a great gift, to be honest.

[#12]

@itlity You will end up with FTTP - eventually. Any results to post, please?

[#13]

Test results were posted just a few minutes ago.

[#14]

Ooops, sorry, I missed them as the page dropped to the last reply, not first unread.

TBH, given the data in your reply, I can see nothing particularly out of place. I need to go out for a couple of hours, but I'll take a closer look when I get back.

[#15]

@itlity 

I presume the OR site didn't show any plans for FTTP.

If you did through the site you'll find an Enquiry page where you can submit a question. Ask if their are any plans, given you're on a FTTP Priority Exchange.

Brian