Work at cabinet affected connection - what next?

Our cabinet was activated for FTTC in November. After the FritzBox correctly identifying a loop inside the house (what a great feature), I was happily running with 0 uncorrectable errors, attainable showing 97697kbit/s down and 33940kbit/s up. I had full 80/20 sync with 8dB SNR.

This remained for 32 days, completely stable, until a couple of Fridays ago at 7am. Suddenly, I am now stuck with 68556kbit/second down with an SNR of 4, and a plethora of uncorrectable errors. The connection is dropping every few days.

Granted, 68mbit is not "slow", and it's within my estimate on the DSLChecker (61-80) so Zen are reluctant to contact Openreach about it since they'll probably say there's no fault, but this is annoying to say the least.

They're working at the cabinet a lot at the minute, presumably others slowly switching to FTTC, and I know crosstalk can drop speeds, but I assume it's not normal to drop 20mbit/sec of speed in one day?
Since Zen are reluctant to contact Openreach they suggested just asking someone next time I see them at the cabinet, but is there a better way?

If you were 1 of the very 1st on the cabinet then it's a perfectly normal drop.

Shows you the sort of speeds you would still be getting if OpenReach had bothered with Vectoring.

8dB SNRM on an 80Mb sync and an attainable of 97Mb doesn't sound right though.
The target SNRM when the service goes live is 6dB.
With an 8dB SNRM that means there's 2dB "spare" which is worth an extra 7-8MB on a good line. Certainly not worth 17Mb.

My guess is that would have been when the line 1st went live, before G.INP was applied.
The line starts with Interleaving and the attainable is exaggerated when interleaved.
If that was the case then ignore that 97Mb attainable.

edit: clarified a point above.

Edited by j0hn83 (Mon 21-Jan-19 11:55:41)

Fair enough when it comes to the attainable values.. I know they're not perfect.

But essentially you're saying going from 79999kbit/sec for 32 days with 0 errors and 8dB SNR (reported by the router anyway) down to 68556kbit/sec with 4dB SNR in 1 hour on a random Friday is "normal"?

Here's the full stats:
Full stats

I've seen more than 20Mb drop from a single crosstalker.

I'm saying a drop of that level when you were the first on the cabinet is not unknown.

Wether an engineer enabled a crosstalker at the cabinet at 7am is another thing.
It's entirely possible though that their service was enabled the day before but the modem wasn't connected/synced till 7am.

I'm not saying this is what happened to you, but yes it's very possible, and is the main cause of sudden speed drops. These drops are usually higher for early adopters.

All the stats from the modem would help.
edit: just noticed the stats.

Edited by j0hn83 (Mon 21-Jan-19 12:13:54)

In reply to a post by j0hn83:

I've seen more than 20Mb drop from a single crosstalker.

Wow. I had no idea it would be that insane. Sigh. It's less the speed, (although I want the speed!), it's the stability that came with it. 80mbps with 0 uncorrectable errors for 32 days sync time, was wonderful.

Also I just checked back on my graph screenshots, you were right, it was 6dB not 8. I misremembered.

attainable suggests a 3dB SNRM target.
Only ever seen DLM lower SNRM in 1dB increments.

You're absolutely positive there was no other resyncs between the line going live and the Friday morning?

I can't believe that.
G.INP is applied 2 days later, this causes a resync.

Over the next few days if the line is stable it will lower the target SNRM in 1dB increments, which causes resyncs.

There must have been at least 1 resync to enable G.INP.

The SNRM dropping doesn't happen with every line, but G.INP doesn't appear from nowhere and needs a resync.

It's also possible lines have been getting gradually added over this time, with would have nibbled away at the SNRM and attainable but wouldn't show as a decrease in sync until a resync was initiated.

edit: auto correct mistake.

Edited by j0hn83 (Mon 21-Jan-19 12:23:22)

Sorry to clarify, the line went live, it was okay for a few weeks but somewhat unstable until I found the internal extensions connected that I mentioned in my first post. I can't recall the exact numbers for the first week or so, it was at that point I spotted the message in the Fritzbox about the extra 8 meters causing a speed drop, disconnected the internal extensions by going in to the test socket (where I have been since) and it shot up to the numbers in my original post. It's at that stage it was online for 32 days.

Ah, that sounds a more logical sequence of events.

The 3dB drop in SNRM your line has seen would increase your sync by around 10Mb.
So if it wasn't at 3dB you would be getting 60Mb, not 70Mb.

This shows the extent of crosstalk, it's worse than it 1st appears.

If you resync at the moment you should get another few Mb and sync around 70-71Mb.

.

Edited by deleted (Thu 24-Jan-19 04:51:58)

.

Edited by deleted (Thu 24-Jan-19 04:51:36)