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Standard User lozzd
(regular) Mon 21-Jan-19 10:48:28
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Work at cabinet affected connection - what next?


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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?
Standard User j0hn83
(experienced) Mon 21-Jan-19 11:54:04
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
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)

Standard User lozzd
(regular) Mon 21-Jan-19 12:06:07
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Re: Work at cabinet affected connection - what next?


[re: j0hn83] [link to this post]
 
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


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Standard User j0hn83
(experienced) Mon 21-Jan-19 12:13:05
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
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)

Standard User lozzd
(regular) Mon 21-Jan-19 12:18:39
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Re: Work at cabinet affected connection - what next?


[re: j0hn83] [link to this post]
 
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.
Standard User j0hn83
(experienced) Mon 21-Jan-19 12:22:21
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
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)

Standard User lozzd
(regular) Mon 21-Jan-19 12:27:02
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Re: Work at cabinet affected connection - what next?


[re: j0hn83] [link to this post]
 
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.
Standard User j0hn83
(experienced) Mon 21-Jan-19 12:31:35
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
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.
Standard User bigbadpirate
(member) Wed 23-Jan-19 21:32:31
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
.

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

Standard User bigbadpirate
(member) Wed 23-Jan-19 21:33:20
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
.

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

Standard User bigbadpirate
(member) Wed 23-Jan-19 21:40:44
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
.

Edited by bigbadpirate (Thu 24-Jan-19 04:52:26)

Standard User Zarjaz
(eat-sleep-adslguide) Sat 26-Jan-19 18:29:52
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
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?

Really ? I find that highly unlikely, Zenís support staff suggested you ask an Openreach engineer next time you see one at the cab ?

It isnít a useful course of action at all, the Openreach staff will have no records to hand of your service, and they also have their own work to be getting on with. What work is going on at the cabinet ? Why must this be the cause ? Have you checked you have clear dialling tone on your line ?

Standard User PhilipD
(experienced) Sun 27-Jan-19 10:19:55
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
Hi

Errors are not a problem as VDSL is designed to work with errors, that's how they stuff so much data through decades old analogue telephone wires.

If you are first on the cabinet then all you will see from now on is a degrading service, that's just how it is, as cross-talk affects everyone to a greater or lesser degree, the difference for you is you have a baseline when it was just you on the service and no cross-talk, most people don't have this so have no idea just how bad a technology VDSL is with cross-talk.

I would just accept the fact as otherwise you will go mad constantly checking the line and trying to fix something you can't.

I was number 2 on the cab at my old address, saw 15db SNR continually drop over the weeks after it went it live to end at about 7db but I was close enough to just hold on to a maximum 80/20. At the new address where VDSL has been live for years and we joined up, I haven't seen any decline as everyone was already there.

Regards

Phil
Standard User lozzd
(regular) Wed 30-Jan-19 10:05:43
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Re: Work at cabinet affected connection - what next?


[re: PhilipD] [link to this post]
 
I guess in a way, if the speed is just going to drop, so be it. But the quantity of speed that was lost in a 5 minute period seems more than just a bit of crosstalk from new customers.

Actually, I don't even midn that much about the speed, it's more that the connection is far less stable now. Dropping every couple of days to resync versus 31 days uptime is irritating.
Standard User PhilipD
(experienced) Wed 30-Jan-19 10:24:39
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
Hi

Telephone cable was never designed for data, it wasn't even that good for voice and audio quality. This has resulted in cross-talk being a big issue as telephone cable was never designed to work with these sorts of frequencies. In many ways it is wrong it's been allowed to happen with telephone cable re-purposed this way as it doesn't perform that well, can be unreliable and difficult to fix, wastes a lot of energy, and was only ever a short term solution that just delays the inevitable when we can have real fibre as opposed to the faux-fibre we have now called VDSL.

If you are first on a cabinet with no cross-talk, then the next customer, especially if living near you so their line is close to yours for a good distance, can easily have a very high impact.

You shouldn't be seeing disconnections every couple of days, but if they are adding more and more customers your profile may be being changed by the kit. Things like power levels can be adjusted downwards to help prevent cross-talk from your line affecting other lines, and it could take a while for things to settle down. Provided normal checks like listening to the phone line for noise shows up nothing, all you can do is wait to see if things settle down.

Regards

Phil
Standard User lozzd
(regular) Fri 07-Jun-19 10:54:27
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Re: Work at cabinet affected connection - what next?


[re: j0hn83] [link to this post]
 
Just in case you wanted a cool graph of just how bad crosstalk is - my area had a scheduled power outage this week and so 100% of people on my cab disconnected (presumably) - except me, for 30 minutes, because of the UPS. Check out the attainable go from 71mbit/sec to 107mbit!
It's a small cabinet too.

Screenshot of graph
Standard User alexatkin
(regular) Sat 29-Jun-19 09:36:05
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Re: Work at cabinet affected connection - what next?


[re: lozzd] [link to this post]
 
In reply to a post by lozzd:
Just in case you wanted a cool graph of just how bad crosstalk is - my area had a scheduled power outage this week and so 100% of people on my cab disconnected (presumably) - except me, for 30 minutes, because of the UPS. Check out the attainable go from 71mbit/sec to 107mbit!
It's a small cabinet too.

Screenshot of graph


I used to be on Digital Region, synced at 100/30 with an attainable of 130Mbit.

Now on the same line I'm stuck at 66.8/20. Granted Openreach use different band plans which did seem to reduce the attainable from day one, but it still shows how shocking crosstalk can be.

I also got a second line which shaved 1-2Mbit off my first line and that's likely from crosstalk only over the drop wire from the pole. If your line is right next to another VDSL pair all the way back to the cabinet, things are likely to be much worse.

Edited by alexatkin (Sat 29-Jun-19 09:37:36)

Standard User tommy45
(knowledge is power) Sat 29-Jun-19 16:01:39
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Re: Work at cabinet affected connection - what next?


[re: PhilipD] [link to this post]
 
In reply to a post by PhilipD:
Hi

Errors are not a problem as VDSL is designed to work with errors, that's how they stuff so much data through decades old analogue telephone wires.

If you are first on the cabinet then all you will see from now on is a degrading service, that's just how it is, as cross-talk affects everyone to a greater or lesser degree, the difference for you is you have a baseline when it was just you on the service and no cross-talk, most people don't have this so have no idea just how bad a technology VDSL is with cross-talk.

I would just accept the fact as otherwise you will go mad constantly checking the line and trying to fix something you can't.

I was number 2 on the cab at my old address, saw 15db SNR continually drop over the weeks after it went it live to end at about 7db but I was close enough to just hold on to a maximum 80/20. At the new address where VDSL has been live for years and we joined up, I haven't seen any decline as everyone was already there.

Regards

Phil
It maybe but BT enforce something called DLM and that sets what threshold of error rate is acceptable
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