topic Re: Understanding High Signal Attenuation in Broadband

Understanding High Signal Attenuation

itlity — Mon, 17 Jul 2023 13:56:51 GMT

Just installed a Hub 2, and wondering whether some of the info it shows may "explain" the dropping of our broadband download speed.

2 to 3 months ago our line went down to 1Mbps and the Openreach engineer -though not-doing-anything- made our line to go back to 12Mbps for a few weeks. We are about 1.2 km away from the street cabinet, just outside a small village in the country side.

I noticed in the Hub info below there is a max download speed at 14Mbps whilst the actual download speed is at 7.9Mbps.

SNR is not good but not that bad, but signal attenuation seems quite high for the distance to the street cabinet: am I reading that right?

Re: Understanding High Signal Attenuation

Anonymous — Mon, 17 Jul 2023 15:42:51 GMT

@itlity

For reference, I am 50 metres from "our" cabinet. My router stats say:

Line attenuation: 2.1 / 4.5

Signal attenuation: 2.1 / 4.7

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 15:51:38 GMT

@itlity A question - are you on an ADSL or FTTC connection? Those figures suggest ADSL to me, but I could be wrong. Of more concern than your attenuation figures is your DSL uptime of only 37 hours - this points to an OR network issue, irrespective of connection type. I will post below my 'help us to help you' script, and await your response before saying much more.

For Community members to be able to help, information from these two sites, as screenshots, posted as pictures within the topic, not as attachments:-

BT Broadband(obscuring your phone number) and BTW Performance Tester - Over a wired (Ethernet) connection if at all possible, please report the 'ADDITIONAL DIAGNOSTICS', and sight of the broadband connection status from your Hub (with the 'Username' obscured) would be a good starting point.

For the Hub One -

Navigate from the Home Screen to Troubleshooting > Helpdesk

For the Hub Two -

Navigate from the Home Screen to Advanced Settings > Technical Log > Information

It may also be a good idea to report the results of a Quiet Line Test - dial 17070 option 2 from a (preferably corded) phone. After the confirmation of your phone number, there should be total silence apart from the regular 'Quiet Line Test' announcement. Any other noise - report a PHONE fault first.

If you are unsure about any of the above, please just ask - I am happy to help.

Re: Understanding High Signal Attenuation

itlity — Mon, 17 Jul 2023 16:06:40 GMT

Thanks for the reply, and script!

I am indeed on an ADSL broadband.

Up time is short as I installed the hub 2 on Saturday morning and router restarted by itself at about 00.30am on Sunday.

Will provide the tests results tomorrow.

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 16:16:53 GMT

Cheers for confirming your connection - the u/s speed threw me as it is a bit high, given your attenuation figures and the capabilities of ADSL.

Re: Understanding High Signal Attenuation

Dan_the_Van — Mon, 17 Jul 2023 17:08:37 GMT

@jab1

The Hub Two Technical Log extract shows VLAN 101 isn't that FTTC ?

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 17:12:44 GMT

@Dan_the_Van Good point, but I'd rather wait until we have a bit more to go on before saying much more - one piece of a jigsaw is not very useful.

Re: Understanding High Signal Attenuation

bmc — Mon, 17 Jul 2023 17:17:42 GMT

@itlity

To provide a bit more detail you could run your phone number in the following.

https://www.broadbandchecker.btwholesale.com/#/ADSL

Post a screen shot of the results, including the narrative. Remember to obscure your details.

Brian

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 17:19:14 GMT

@bmc Already covered in my 'help us to help you' script, posted above.

Re: Understanding High Signal Attenuation

Dan_the_Van — Mon, 17 Jul 2023 17:19:15 GMT

@bmc

That has already been requested

@jab1

Over the years in support I've seen many a diagnosis go wrong because of an assumption, just helping to ensure this doesn't happen here.

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 17:21:53 GMT

Fair enough, @Dan_the_Van - hopefully the details I have requested will make a full jigsaw. 😉

Re: Understanding High Signal Attenuation

bmc — Mon, 17 Jul 2023 17:24:18 GMT

@jab1

Sorry - mis-read your post and didn't realise you were speaker about the Checker.

Brian

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 17:31:13 GMT

@bmc My 'help sheet' is always the same - it would be a macro if I could remember how to create them.

Re: Understanding High Signal Attenuation

RealAleMadrid — Mon, 17 Jul 2023 19:06:07 GMT

@jab1 if the stats show VLAN 101 it must be FTTC, however the OP who seems to think it is ADSL will not be responding until tomorrow.🤔

Re: Understanding High Signal Attenuation

jab1 — Mon, 17 Jul 2023 19:17:53 GMT

@RealAleMadrid Agreed - after Dan's query earlier I refreshed my memory. When I get all my ducks in a row (all the requested data) then I'll have another think, but my current thinking is the OP is in a very rural location, with a looong copper wire, but still with problems , looking at the 'current' and 'attainable' d/l figures - and a couple of other stats on that grab.

Re: Understanding High Signal Attenuation

Anonymous — Tue, 18 Jul 2023 07:55:42 GMT

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

Re: Understanding High Signal Attenuation

jab1 — Tue, 18 Jul 2023 08:02:11 GMT

@Anonymous 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.

Re: Understanding High Signal Attenuation

Anonymous — Tue, 18 Jul 2023 08:13:25 GMT

@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?

Re: Understanding High Signal Attenuation

jab1 — Tue, 18 Jul 2023 08:30:05 GMT

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?

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

Re: Understanding High Signal Attenuation

MisterW — Tue, 18 Jul 2023 08:42:04 GMT

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.