Lost about 10mbps

I had a very short power cut a couple of days ago.
And now my TBB speed tests show a lose of about 10mbps.
I am with Daisy Wholesale [SSE] on a 80/20 FTTC package.
The DLM would not react to a five minuet power cut , surely.?

What stats does the modem show ?

DSL Uptime
5 days 22 hours 37 minutes 3 seconds

DSL Type
VDSL2

DSL Mode
Fast

Line Rate
�i 20 Mbps �h 71.71 Mbps

Data Transferred
�i 750.69 MBytes �h 3849.2 MBytes

Output Power
�i 6.8 dBm �h 13.5 dBm

Line Attenuation
�i 6.2, 19.9, 29.4 dB �h 10.5, 23.5, 35.5 dB

Noise Margin
�i 10.2 dB �h 6.4 dB

The modem/router does not show more.

Edited by deleted (Sun 10-Mar-19 23:15:37)

What DLM does depends on the way the power cut happened.

If it went off "bang", like you just pulling the power plug out, no I doubt if it would. But if it flickered on and off a few times, which you might not even notice, with all sorts of electromagnetic noise during all that, then the error counts on the line would have gone through the roof and caused a reaction from it.

That noise could in fact have been occurring for a while before the power actually went off. Same bad effect on DLM.

Edited by RobertoS (Sun 10-Mar-19 23:16:46)

In reply to a post by RobertoS:

What DLM does depends on the way the power cut happened.

If it went off "bang", like you just pulling the power plug out, no I doubt if it would. But if it flickered on and off a few times, which you might not even notice, with all sorts of electromagnetic noise during all that, then the error counts on the line would have gone through the roof and caused a reaction from it.

That noise could in fact have been occurring for a while before the power actually went off. Same bad effect on DLM.

You could say that it was the same as pulling the plug as the house power just went off.

Read my post again. Maybe the edit wasn't there when you started your reply .

In reply to a post by RobertoS:

Read my post again. Maybe the edit wasn't there when you started your reply .

Same reply:
You could say that it was the same as pulling the plug as the house power just went off.

[shrug]
"You can lead a horse to water, but you can't make it drink".

Edited by RobertoS (Sun 10-Mar-19 23:42:18)

In reply to a post by ironman12345:

Noise Margin
�i 10.2 dB �h 6.4 dB

Maybe your line has a 6dB noise margin target but has been slowly going below it (e.g. due to increased crosstalk), and DLM set a 70M cap to restore it to 6dB. The power cut forced a resync at which point it applied this cap.

Hi

It may just be cross talk and the power cut hasn't really caused anything, it's hard to know unless you have a before and after picture of the line.

VDSL has all sorts of tricks it applies to help reduce the impact of cross-talk and so some lines may have some speed sacrificed in order for someone else to get something a bit faster. Other customers may have come on line in the days or weeks before the power cut which caused cross-talk to your line but it was still able work okay at a reduced margin.

So if you've had a power cut in the area then it's likely most or all connections to the cabinet also dropped. This means on power back up, you have potentially a hundred or more VDSL modems all trying to sync back up at the same time and you end up with a different noise profile, it's like shuffling a back of cards. So the status quo of noise is different, and you can end up with a better or worse speed. As time goes by things may settle back to as before, they may not.

Unfortunately this is the limitation of the technology, it's quite fickle. Roll on having real fibre to the home.

Regards

Phil

I remember back to 2017 when my local area suffered power cut off with very high flicker on/off for over 40 minutes then next day DLM has capped my line at 74Meg from 80Meg and staying there for 61 days before PN force BTw to resetted DLM via remotely and the banded has been removed. When there was a power cut, GEA test come back with a massive 20 retrains on the line that caused to be banded on the line.

In reply to a post by candlerb:

In reply to a post by ironman12345:

Noise Margin
ƒi 10.2 dB ƒh 6.4 dB

Maybe your line has a 6dB noise margin target but has been slowly going below it (e.g. due to increased crosstalk), and DLM set a 70M cap to restore it to 6dB. The power cut forced a resync at which point it applied this cap.

This, but without DLM being involved. The line isn't capped.

Likely crosstalk (new lines activated on the cabinet) have slowly eaten away at the noise margin (SNRM).
The lines max attainable (maximum potential sync speed) drops when some new lines go live on the cabinet but the line remains connected at the same speed until it reconnects.

The power cut forced that resync and resulted in the line reconnecting at a lower rate.
DLM won't be involved.

The line is synced at 71.71Mb with the default noise margin. There is no spare SNRM for more speed so DLM isn't limiting the line.

That's as good as it gets now. Crosstalk degrades most lines that aren't within a stone's throw of the cabinet due to the lack of Vectoring.

If it went off "bang", like you just pulling the power plug out, no I doubt if it would. But if it flickered on and off a few times, which you might not even notice, with all sorts of electromagnetic noise during all that, then the error counts on the line would have gone through the roof and caused a reaction from it.

A power cut that results in multiple resyncs is pretty obvious if you're home at the time.
Power going on and off quickly won't give enough time to establish sync.
A powered on modem takes over a minute to sync to VDSL2.
Add the modem boot time to that and in most cases it's over 2 minutes.

The OP indicates the power just went out like pulling a plug.
I'd notice my power coming back on for 2 minutes.

A 6db SNR does not always mean a line is not capped. Plenty of power saving technologies exist to reduce power consumption, often this can be playing with interleaving vs output power etc.

Lookup tools such as ASSIA DSL Expresse Power Management, which is leveraged by Sky as one example.

I'm aware these things are possible, but are not used.
The OpenReach FTTC DLM doesn't adjust power levels.

The only DLM line profiles adjustments are

Sync speed (banding).
SNRM target (6dB for ECI and 3/4/5/6dB for Huawei)
Error protection (Interleaving, retransmission or Fastpath)

The OP's line isn't being restricted by DLM, period.

In reply to a post by j0hn83:

A power cut that results in multiple resyncs is pretty obvious if you're home at the time.
Power going on and off quickly won't give enough time to establish sync.
A powered on modem takes over a minute to sync to VDSL2.
Add the modem boot time to that and in most cases it's over 2 minutes.

The OP indicates the power just went out like pulling a plug.
I'd notice my power coming back on for 2 minutes.

I know and have known all that for years, but I wasn't writing a training manual.

I hope you also know that a lot of strange things can happen on the mains supply for many seconds spread over several minutes before the power goes off "like pulling a plug".

I also know from decades of supporting customers in the field that broad brush statements such as that one the OP made can not be fully trusted. What time of day was it? What lights were on? What radios were on that didn't crackle.

Mains power easily seems to a householder to "go off like pulling out a plug". That doesn't mean the power had been stable for the previous few minutes.

If you care to study my original post I'd be very surprised if you can find anything there that isn't true and correct, and nothing that contradicts what you personally and I would realise when we have power cuts.

There has been no suggestion from the OP that there were multiple re-sync's, nor from myself.

I do not agree that purely based on an SNR of 6, you can conclude a line is not being restricted.

I have seen banding applied at speeds that yield SNR of 6db on most resyncs, to lines which previously had 3db noise margin targets. I did not conclude the lines was unaffected 100% by DLM.

You cannot say "period" - I broadly agree with your statement, I cannot say it's 100% the case.

I also disagree that power supply issues are always this black and white.

Edited by ukhardy07 (Mon 11-Mar-19 18:40:41)

In reply to a post by ukhardy07:

I have seen banding applied at speeds that yield SNR of 6db on most resyncs, to lines which previously had 3db noise margin targets. I did not conclude the lines was unaffected 100% by DLM.

I broadly agree, however.... 71.71Mb is not a banded figure, "period".

The line may well be banded at 74Mb but if it is line isn't being restricted by this as it is syncing below it.

OpenReach use fixed banding levels. The 1st banding level below 80Mb is 74Mb.
I believe the next banding figure below 74Mb OpenReach use is 68Mb, though I'd happily be educated on any inbetween those.

Modems sync exactly at the banding figures or a few Kb/s below.
Such as 80,000 or 79,999 or 79,997
The OP's device would show it as 80.0Mb or 79.99Mb

Given the above I say with confidence that the OP's line is not being held back by DLM banding.

I'm also very confident in saying this isn't a result of the SNRM being increased.
DLM moves the SNRM target in 1dB increments. It would take at least 2dB to get the OP to 80Mb.
If DLM has increased the SNRM target then the line has gone from 5dB to 6dB.
Each 1dB is worth around 3-4Mb on a good line that makes good use of the D3 band, less on shorter lines that only use the D1 and D2 bands.

The OP could request a GEA test from their ISP to confirm if the line is banded, and if it has retransmission (required for sub 6dB SNRM targets).
The DLM line profile shown in all GEA tests on all ISP's is 13 days old so this would need done 13 days after the power cut.
Plusnet are happy to share GEA test results and I would guess the likes of AAISP, Zen, Uno, IDNet would also be happy to share this with customers.
No such luck from many of the big players.

In reply to a post by RobertoS:

In reply to a post by j0hn83:

A power cut that results in multiple resyncs is pretty obvious if you're home at the time.
Power going on and off quickly won't give enough time to establish sync.
A powered on modem takes over a minute to sync to VDSL2.
Add the modem boot time to that and in most cases it's over 2 minutes.

The OP indicates the power just went out like pulling a plug.
I'd notice my power coming back on for 2 minutes.

I know and have known all that for years, but I wasn't writing a training manual.

I hope you also know that a lot of strange things can happen on the mains supply for many seconds spread over several minutes before the power goes off "like pulling a plug".

I also know from decades of supporting customers in the field that broad brush statements such as that one the OP made can not be fully trusted. What time of day was it? What lights were on? What radios were on that didn't crackle.

Mains power easily seems to a householder to "go off like pulling out a plug". That doesn't mean the power had been stable for the previous few minutes.

If you care to study my original post I'd be very surprised if you can find anything there that isn't true and correct, and nothing that contradicts what you personally and I would realise when we have power cuts.

There has been no suggestion from the OP that there were multiple re-sync's, nor from myself.

I do not know the reason , all I know is that the power to the house went off.
If I had pulled the modem/router power supply plug out , it would have been the same.
After about 5 minutes the power returned and that is when the lose happened.
So It could have been re-synced at that time.
Anyway I can use the line and it might recover in time.
Thanks for all the posts.

I broadly agree, however.... 71.71Mb is not a banded figure, "period".

Good point, this had not crossed my mind.

I'm also very confident in saying this isn't a result of the SNRM being increased.
DLM moves the SNRM target in 1dB increments. It would take at least 2dB to get the OP to 80Mb.
If DLM has increased the SNRM target then the line has gone from 5dB to 6dB.

Good point also, I stand convinced. Nothing you have said is "news" but honestly I had never really applied it in practice, so some good takeaways for future.

I'm afraid my post, which was a reply to j0hn83, can seem to read as if I didn't trust what you said. That wasn't my intention, so I apologise.

It was more of a general comment that although all of us say honestly what we experience when things happen to us or when we witness a scene, we may not be entirely accurate about the actual facts of the event. Facts that we very possibly wouldn't be aware of.

In reply to a post by RobertoS:

I'm afraid my post, which was a reply to j0hn83, can seem to read as if I didn't trust what you said. That wasn't my intention, so I apologise.

It was more of a general comment that although all of us say honestly what we experience when things happen to us or when we witness a scene, we may not be entirely accurate about the actual facts of the event. Facts that we very possibly wouldn't be aware of.

NP RobertoS , It just seemed funny to me that it was fine before the power cut.
But tech is like that.
I could not find anything wrong with a TV I was called out to , but it just would not work.

I've lost 20Mbps since my move from Sky to Plusnet yesterday.
I used to get constant 74mbps downloads over the lan. I'm now getting 54ish.

http://forums.thinkbroadband.com/plusnet/t/4614851-r...

So unlikely to be a different port on the DSLAM, most likely is that you had been on a 4 or 3db profile which has been reset back to 6 with the move.

Are you using a different CP router now ?

I�m using the same tp-link archer vr900 which comes pre-configured with multiple isp�s settings. I�ve only changed it from sky�s mer to Plusnet.

Profile change or G.INP turned off during migration, which usually happens when I move my line every 12/18 months

Leaving things alone it usually returns after a week or two

That's encouraging.
I will leave things alone and hope for the best.

You probably also changed underlying Openreach product. That automatically rested DLM back to the 6dB target noise margin and possibly heavy interleaving plus at least 8ms additional latency. As Andrew says, that will self-correct quite quickly.

Once the correction kicks in two things happen. The target SNRM will drop by 1dB steps (and auto-resync each time), and G.INP can be enabled which removes classic interleaving that costs many Mbps and sets interleaving to 8/12/16, with zero additional latency.

In reply to a post by Mitchy_mitch:

I've lost 20Mbps since my move from Sky to Plusnet yesterday.
I used to get constant 74mbps downloads over the lan. I'm now getting 54ish.

http://forums.thinkbroadband.com/plusnet/t/4614851-r...

Same thing happened to me moving from PN to IDNet. It eventually recovered under slightly odd circumstances a few months later.