topic Re: Hmmmm here we go again... in Full Fibre

Hmmmm here we go again...

BobR1 — Wed, 29 Dec 2021 11:12:58 GMT

Downstream SNRM very high at 6.9dB it is usually 5.3 to 5.5dB so speed is being constrained.

Just checked and the modem uptime has been reduced from 40something days to just under 26hours so clearly a powercut at around 09:00 yesterday. The curious thing is it did not reset any of the other clocks in the house and I didn't even notice anything at the time, so must have been very brief.

I'll monitor for a few days to see whether things get back to normal. Failing that it will be yet another ticket raised.

Re: Hmmmm here we go again...

jab1 — Wed, 29 Dec 2021 11:34:32 GMT

@BobR1 That uptime reduction is unlikely to be a 'powercut' as such, more likely something within the BT network.

Re: Hmmmm here we go again...

Mustrum — Wed, 29 Dec 2021 11:38:37 GMT

Why raise a ticket for one drop you did not even notice?

Re: Hmmmm here we go again...

BobR1 — Wed, 29 Dec 2021 11:59:07 GMT

@Mustrum

The issue is not the drop it's the effect i.e. slower speed due to higher SNRM!

Re: Hmmmm here we go again...

Mustrum — Wed, 29 Dec 2021 12:12:07 GMT

@BobR1 I guess it is all relative, that said you did not your speeds.
But given the time of year, Christmas tree lights, new “toys” and other electrical interference, to a degree small changes should be expected.

Have you noticed any significant difference in speed?

Re: Hmmmm here we go again...

Gandalf — Wed, 29 Dec 2021 15:18:21 GMT

Thanks for your post @BobR1

I'm sorry to see you're having speed issues.

I've tested your line today and the tests aren't showing any issues or artificial restrictions on your line we can remove.

As the tests are passing and your speeds are within/above our suppliers expectations of between 35mbps to 51.1mbps, I'm afraid there's nothing we'd be able to do to investigate further as an engineer wouldn't look into this.

Unfortunately I think this would be a case of waiting for DLM (dynamic line management) at the cabinet to bring the SNRM back down automatically at some point though I can't say when that'll be.

If you're interested I've attached below a copy of the testing and diagnostics I've run:

GEA Service Test

Test Outcome	Pass
Test Outcome Code	GTC_FTTC_SERVICE_0000
Description	GEA service test completed and no fault found .
Main Fault Location	OK
Sync Status	In Sync
Downstream Speed	60.2 Mbps
Upstream Speed	10.2 Mbps
Appointment Required	N
Fault Report Advised	N
NTE Power Status	PowerOn
Voice Line Test Result	Pass
Radio Frequency Ingress	Not Detected
Repetitive Electrical Impulse Noise	Not Detected
Cross Talk	Not Detected
Estimated Line Length In Metres	778.4
Upstream Rate Assessment	Good
Downstream Rate Assessment	Very Good
Interference Pattern	Regular Interference Observed Daily
Service Impact	No Impact Observed
Interference Duration Longest Occurrence	;00:00to23:45
Interference Location	Customer Premise
Interference Observed In Days	14
Home Wiring Problem	Not Detected
Downstream Policing Discard Rate	0.0
Customer Traffic Level	Upstream and Downstream traffic detected
Technology	VDSL
Current 15Min Bin Retrains	0
Last 15Min Bin Retrains	0
DP Type	External
Profile Name	0.128M-80M Downstream 4dB, Retransmission High - 0.128M-20M Upstream, Error Protection Off
Time Stamp	2021-12-16T15:15:00

Parameters	MIN	MAX	AVG
Down Stream Line Rate	63.6 Mbps	75.7 Mbps	66.4 Mbps
Up Stream Line Rate	10.1 Mbps	10.3 Mbps	10.1 Mbps
Up Time	710.0 Sec	900.0 Sec	899.3 Sec
Retrains	0.0	2.0	0.0

Current and Last 15 Minute Bin Performance
Parameters	Last Traffic Count(Upto 15 mins)	Current Traffic Count(Upto 15 mins)
Start Time Stamp	2021-12-29T14:42:51Z	2021-12-29T14:57:51Z
Ingress Code Violation	0	0
Egress Code Violation	0	0
Errored Seconds	0	0
Severely Errored Seconds	0	0
Unavailable Seconds	0	0

RRT Diagnostics

Speed Estimates

Re: Hmmmm here we go again...

BobR1 — Thu, 30 Dec 2021 15:19:43 GMT

Hi Gandalf and thanks for those test results.

Interestingly, earlier today it wasn't much different from yesterday.

However, I just logged in on my PC a few minutes ago and I see that the modem uptime is only 1H25m. Not caused by me as I was not at home and the bband connection was not in use by anyone at my end when the modem reset. Downstream SNRM is showing 6.2dB and the, somewhat academic, max attainable is being reported as 74.265Mbps.

I'll run a BTW speedtest in a minute to see what is being reported.

Re: Hmmmm here we go again...

BobR1 — Thu, 30 Dec 2021 15:27:11 GMT

BTW speedtest reports 55.89Mbps downstream which is pretty much what I would expect normally - although I have seen it go higher when the SNRM down is around 4.o to 4.5dB. Not very often though.

Re: Hmmmm here we go again...

leew88 — Sat, 01 Jan 2022 21:23:41 GMT

The SNR values is the other way round, ie the higher the better:

The value of 'Noise margin' [dB]:
up to 6 dB — a low-quality line, there are synchronization problems;
7 dB to 10 dB — failures may occur;
11 dB to 20 dB — good line, no synchronization problems;
21 dB to 28 dB — a very good line;
29 dB and above — an excellent line.

Moderators Note: This post contains incorrect information, please disregard it.

Re: Hmmmm here we go again...

RealAleMadrid — Thu, 30 Dec 2021 16:07:25 GMT

@leew88 You are totally wrong about SNR values and I would delete that post if I were you it is not true and frankly absolute nonsense, I believe it comes from some American document and bears no relation to reality on UK broadband lines. SNRM values of 6dB and below are perfectly normal on FTTC circuits. My FTTC line which syncs at full 80/20 speeds has a lower than usual SNRM of 1.7dB and has been connected for over just under 50 days with a total of 2 CRC errors and 2 Error Seconds reported. That doesn't look like a low-quality line to me.🙄

Re: Hmmmm here we go again...

leew88 — Thu, 30 Dec 2021 16:20:07 GMT

No worries, thanks for clarifying, doesn't help that there's confusing info out there

Re: Hmmmm here we go again...

Townman — Sat, 01 Jan 2022 21:10:35 GMT

The information has to be taken in context. For a FIXED sync speed a higher SNRM is better, however in terms of getting the best out of a line's ability, SNRM and speed are inversely linked.

Lower SNRM delivers a higher speed with potentially poorer stability.

Higher SNRM delivers lower speed with higher stability.

So that advice holds water totally at the expense of speed ... Which is what most people take to be best / better.

Re: Hmmmm here we go again...

BobR1 — Mon, 03 Jan 2022 06:48:24 GMT

This is getting beyond a joke!

My DSL connection is being reset almost daily in the early hours of the morning around 02:30. I suspect there's not a lot of user traffic going through the DSLAM at that point in time and my modem is not being reset at the same time so that's not the cause. When I logged in this morning the Downstream SNRM was set at 7.8dB. I really don't think my connection needs that level. In the past it has run for extended periods of time at somewhere between5.3 and 5.5ddB.

The BTW speed test doesn't show much of an impact on the speeds it registers and the additional diagnostic says the downstream IP profile is 58.11Mbps.

Who or what sets that profile? The upstream profile is 20Mbps so why isn't the downstream profile 80Mbps? I do understand that I'm never going to get that speed but I've had better than the 55.6ishMbps that I'm currently getting.

Basically all the messing around with the downstream SNRM is leaving me with NO CONFIDENCE that I'm getting the best that's achievable from my Plusnet connection!

Re: Hmmmm here we go again...

Anoush — Mon, 03 Jan 2022 07:04:23 GMT

Drops in the early hours of a morning would suggest either maintenance or DLM induced drops at the DSLAM. As suggested earlier, the profile changes are done by DLM at the DSLAM in the cabinet automatically.

The downstream IP profile isn’t 80mbps because your sync speed your router has negotiated with the cabinet (due to various factors such as the quality of the line and the length of the line) isn’t anywhere near this.

Looking at my previous post Here the downstream IP profile is set (automatically) at between 90 to 96% of your sync speed, this is not something we control.

~~If you can post up your router stats in particular the part where it says “maximum attainable” this may provide more of an idea if there’s room for improvement.~~

[edit]

Ah I see you’ve already posted the maximum attainable

Re: Hmmmm here we go again...

BobR1 — Mon, 03 Jan 2022 07:19:01 GMT

Hello Anoush, I really don't know what's going on, the downstream SNRM is now 13.5dB following a DSL reset. This is ridiculous. Stats attached.

Re: Hmmmm here we go again...

BobR1 — Mon, 03 Jan 2022 07:26:30 GMT

Anoush, I am minded to reset my Zyxel modem/router but not sure if that would just make things even more confused. What do you think?

Re: Hmmmm here we go again...

BobR1 — Mon, 03 Jan 2022 09:09:03 GMT

OK I decided to bite the bullet and power down my Zyxel VMG8924-B10A modem/router. Will leave for at least 30 mins to cover two DLM cycles.

Powered up again 08:54 and at least the downstream SNRM has reset from the ludicrous 13.6 dB to 7.1dB. Still higher than I would expect.

Will monitor now and see what happens over next few days.

Re: Hmmmm here we go again...

TheMightyAJ — Mon, 03 Jan 2022 11:57:15 GMT

Thanks for that @BobR1. Just let us know how things go and we'll be happy to pick this one back up for review