Noise margin increased (Sky FTTC)

Hello all. I am on the Sky 40/10 FTTC package and currently get 37 down and 9.5 up. I am also to be upgraded to Sky's faster package for free over the next few months according to the email they sent. I noticed yesterday that my noise margins for both up and down have increased (download noise margin from 9.5db to 13db, and upload from 9.9db to 10.10db). Is this likely to be noise on the line, or conversely I am likely to see a healthier increase in speed when switched over to the faster package do you think, given the possible improvement in headroom? Many thanks.

This would indicate less noise on the line, so faster speeds once upgraded. It is the "safety margin" between the signal, and noise.

Thanks AndyPandy. Good to know. I thought it might have gone up because there was more noise on the line, then once I upgraded the speed might be lower until the noise lowered again!

If there is more noise the margin will actually go down

Of course, makes sense as it's the margin I'm looking at. That's good to know then. Thanks again AndyPandy and MrSaffron.

And the inverse is true: if DLM decides to reduce your speed, the noise margin will go up.

When Sky raises the cap on your service, the noise margin will go down. DLM will likely increase your speed until the noise margin falls to 3dB (for a Huawei DSLAM anyway), unless your new cap is hit first.

Candlerb - I'm on a Huawei cabinet so seeing it drop to 3db would be good (assuming my line is capable of course). The adsl checker from BT indicates my postcode should get high sixties if it's not impacted (suspect mine might be though) and as I'm with Sky I can't use the phone number check for a more accurate assessment.

Since my cabinet went live. I started on the 23dB noise margin, since more and more people started ordering the VDSL service, the noise margin now stands at: 10.7dB

Line stats:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 35369 Kbps, Downstream rate = 95496 Kbps
Bearer: 0, Upstream rate = 19999 Kbps, Downstream rate = 79999 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 10.7 19.8
Attn(dB): 7.8 0.0
Pwr(dBm): 13.4 -8.2

But you're lucky in that you have a very short line and your attainable speed is in excess of what the line will support. I have been on my cabinet for about 6 years, but within the last few months a second smaller Huawei cabinet appeared alongside it, so maybe that has something to do with my noise margin increase?

Another cabinet with the prospect of more people with VDSL2 and thus more crosstalk would normally lead to lower noise margins

Fair point MrSaffron! Nothing has changed with setup or in the house. Maybe a neighbour has gone away for a few weeks!

In reply to a post by giggsy1977:

But you're lucky in that you have a very short line and your attainable speed is in excess of what the line will support.

Care to explain how an attainable can be higher that what a line will support?

The max attainable is the maximum that a line will support.

In reply to a post by MHC:

The max attainable is the maximum that a line will support.

Except that in these days of 6/5/4/3dB FTTC noise margin settings it isn't. Quite apart from it fluctuating continually.

I think the poster you replied to simply worded his post badly, if you look at what he was replying to.

Edited by RobertoS (Tue 13-Nov-18 10:40:19)

Thanks RobertoS - I did indeed word my response badly. MHC - what I meant to say is that max360 is on an 80/20 plan, but the line is capable of more throughout as evidenced by the max attainable rate of the line, not that speed above 80/20 would be achieved as the product doesn't permit that.

Quote
"The adsl checker from BT indicates my postcode should get high sixties if it's not impacted (suspect mine might be though) and as I'm with Sky I can't use the phone number check for a more accurate assessment."

giggsy1977 You may get a more accurate result by using the address checker.
If not, the number of a nearby neighbour on a bt / reseller line certainly will.

Thanks gymno74 - it was the address checker I used as I don't know anyone on BT unfortunately to check. I have noticed over the years that my estimated speed has gone up (a little) and I have used a neighbours address and there's is a little lower than mine. Guess it depends how the cable is routed.

Ah ok.
I thought maybe you'd used the specific postcode checker & missed the address one.

I should have known better than that.

Happy for any help or guidance on such matters so feel free!

In reply to a post by gymno74:

Ah ok.
I thought maybe you'd used the specific postcode checker & missed the address one.

The pure Postcode checker no longer gives FTTC/VDSL/FTTP data. It doesn't even show the lines.

If you enter just the postcode into the Address checker you get a list of all the addresses in that postcode, and can include several different cabinets. You can check the estimates for all products for each address. (Database errors excepted).

That is what giggsy was using .

Thanks RobertoS, i haven't used the checker for at least 2 months & wasn't aware of the change.

No problem.

The trouble with the Postcode-only checker is that although it works reasonably well for ADSLx where total line length from the exchange is the important factor, it cannot work well for FTTC as any particular postcode can be served by multiple cabinets around it. Including of course possibly one within it.

Conversely, any particular cabinet can serve addresses in several postcodes.

For FTTC the postcode checker only reported the data for the first one it found in the database. Which might be 20 metres from the premises or the diametrically opposite side of that postcode area. With premises at tat distance being 20 metres from some other cabinet, to which they were connected.

There must have been loads of complaints, so they did the easiest thing. Stopped it reporting on FTTC etc. So for "fibre", never use it.

The list in the Address checker solves that, as I said . Always did, and to some extent still does on ADSLx. Which is why the checker itself says number is best, address is next best.

For FTTC the postcode checker only reported the data for the first one it found in the database.

This i didn't know.

That's the one I used yeah! Noise margin has dropped on the download to 10db overnight. Upload remains the same though. 😕

Went back up to 13db again before I left for work. Do you think there's a line fault? Should I contact Sky? Thanks all.

Can be a dozen different things, line fault is least likely.

Can be a neighbours (crosstalker) modem being turned on and off.
My very first crosstalker turned their modem off every night between 10-11pm and this showed as a 1.2dB jump in SNRM.
It dropped again between 7-8am when they turned the modem back on.

It could also be an appliance, like a pump/heater/generator/etc either on your premises, near it, or anywhere near the line between you and the cabinet.

Running a program like DslStats with a compatible modem to graph the snrm changes can help diagnose these things but more often than not they remain a mystery.

I'm sure you're right jOhn83. I was looking for a replacement router but will wait until after my speed upgrade I think. I check the SNR quite regularly and it's been at the same level for a long time. Only gone up this last week or so, so something has changed somewhere! Thanks.