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[burakkucat]

That didn’t last long. The so-called ‘repair’ failed on Sat afternoon.

    Line two or line four?

[Weaver]

Oh sorry, line 2. The moaning OR engineer will be back to the scene.

[Alex Atkin UK]

I wonder how many engineers book the day off when they see you reported a job?

[Weaver]

We don’t always get the same fellow, not at all. But we have been getting him quite often in the last year or so.

Here’s the pretty line 2 picture from A&A:

[Weaver]

Now as well as the line 2 second failure, last night, Sunday, Line 4 dropped to downstream 1.67 Mbps approx, so AA has booked two more OR appointments for me.

[Chrysalis]

Is it stable with a higher SNR margin?

[Weaver]

Good point Chrys. The downstream SNRM has drooped all the way down to 1.1 dB. That’s pretty useless. My modem well-being summary program goes mental, ringing bells about line 2: suffers from low downstream SNRM, ridiculous ES and CRC count right now, and early-stage but very distinct HCD. I’ve just forced a resync and I’ll see what it’s like. But after that I’m following your advice, and if need be I’ll increase the downstream target SNRM to 6 dB until Openreach turn up. Again.

[Weaver]

Engineer here today, very friendly and helpful. Booked to look at both lines 2 and 4. The lines wouldn’t play ball though. I’ve been quite exhausted and unwell over the last couple of days so I’ve missed what’s been going on with the lines. Line 2 recovered on Sunday afternoon and has been perfect ever since, and line 4 had no problems over the same period. Power was off for many hours yesterday so I wasn’t recording stats. Today I can’t see anything wrong in the slightest with line 4; line 2 shows the smallest case of HCD, but nothing wrong as a result apart from a small speed loss. When I feel a bit better this evening, I’ll review everything.

Talked to engineer at length; showed friend johnson's HCD picture for line 2 and explained that it was a symptom of future trouble. Showed line 1 SNR vs tones curve for comparison. Then showed AA clueless CQM history line 2 and the badness on Sat and Sun, but goodness ever since, apart from the power outage on Tue. Our friend told me that the extreme north of the island is already equipped with FTTP; Gleann Dàil and Dùn Tuilm are two of the remotest spots in the north. He said OR engineers themselves are doing surveys up there, presumably because there simply are no contractors. I also heard about a holiday cottage where an owner had paid £20 for FTTPoD. Is that 1 Gb&bps?

A colleague is taking a look at line 2 from the PCP at the Claymore restaurant on the main road, using some additional software and or hardware, AJAX he might have said but he too was unsure about the name. This should hopefully provide some more insight.

[burakkucat]

I also heard about a holiday cottage where an owner had paid £20 for FTTPoD. Is that 1 Gb&bps?

Isn't there a k (kilo) multiplier missing from that sum? £20k would be more like it. 

As for the speed, it would be whichever Openreach product the ISP is selling onto the end-user.

[Weaver]

I see. I was thinking of the fact that the B&B will actually be offering supposed 1 Gbps to visitors, what, 450 Mbps being the true figure, no? Any more being a matter of luck.

After the engineer had left, I emailed AA straight away, because the speed of line 4 was down to 1.1 Mbps downstream. AA sent me a reply which I missed because I was asleep. When I woke up, a couple of hours later, I looked at that modem and saw HCD had appeared for the first time in many days, as it had gone into hiding for a while for part of last week and into weekend. AA tried to perform a remote SNR reset to restore sanity to the very high downstream SNRM, but for some reason the remote <something> failed so they had asked me to do it. Telnetted into the modem and forced a resync, which had the desired effect, the downstream SNRM being back to 3dB and the downstream sync rate is currently 2161 kbps, about 500k below what it should be because of the >6dB deep HCD. Will perhaps need to increase the d/s target SNRM I suspect, if the error rate is up, as has happened before with HCD. Will check error rates later. Usual pictures of horror available showing initial HCD depth this afternoon and the SNR-vs-time history too.

[burakkucat]

I see. I was thinking of the fact that the B&B will actually be offering supposed 1 Gbps to visitors, what, 450 Mbps being the true figure, no?

If the circuit is provisioned as the Openreach 1 Gbps product then, after taking into account the Ethernet frames and other overheads, the data throughput will be ~940 Mbps. You might like to have a look at GigabitEthernet's "FTTP questions" thread.

[Weaver]

Apologies, I was thinking that 450 Mbps is the only guaranteed throughput figure - is that vaguely right or nonsense? That 900 Mbps is an ‘if you’re lucky’ figure if few other users are around ?

[burakkucat]

Apologies, I was thinking that is it 450 Mbps is the only guaranteed throughput figure - is that vaguely right or nonsense?

I'll have to let someone else answer that question, as I have zero experience (as an end-user) of such a service.

That 900 Mbps is an ‘if you’re lucky’ figure if few other users are around ?

Basically "yes". A GPON, as built by Openreach in the UK, has a 2.488 Gbps DS (to the end users) and a 1.244 Gbps US (from the end users) upper limit. Openreach plans and deploys GPONs with a 1:32 split (but only use the first 30, keeping the final 2 in reserve).

The next pon up in the series is XGPON which, if I am remembering correctly, has a 10 Gbps DS and a 2.5 Gbps US upper limit.

Then there is XGSPON which is symmetrical XGPON, with a 10 Gbps DS and 10 Gbps US upper limit.

(Of course none of that has anything to do with the HCDs you are seeing with your ADSL2 circuit(s)!)

[Weaver]

No, but it’s very valuable! And I believe it was I who started it.

[burakkucat]

Yes, you did. 

I was just a little concerned that a passing moderator might take some action, as we have meandered way off topic.