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Gateways and FEC errors

Haybasha
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Posts: 157
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Registered: 07-05-2014

Gateways and FEC errors

Can anyone tell me why I see tens of thousands of FEC errors per second at random times during the day and evening on certain gateways but not on others?
I use a ZyXEL SBG3300-N with DSLStats and have reported this to PlusNet in the past, including graphs but as yet they have not been able to see this issue live for themselves.
Not sure if anyone else has the same issue and sorry can't be more specific but I'll start logging the gateways that are giving me problems.
16 REPLIES
sjrinfroyle
Grafter
Posts: 895
Registered: 08-05-2011

Re: Gateways and FEC errors

FECs are corrected errors, so the fact they are there is fine really, it just shows you have quite a noisy line but the interleaving is doing its job to minimise the uncorrected errors (CRCs, ES and SES).
They aren't linked to the gateway you're connected to at all (in fact they're not even related to the Internet connection, it's literally just the connection between you and the exchange/cabinet), so I think it is a strange coincidence that you appear to get more FECs when connected to certain gateways.
Is there anything else happening when you get these FECs? I think it might be interference.
Haybasha
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Posts: 157
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Registered: 07-05-2014

Re: Gateways and FEC errors

No other issues at all that I have noted but I see the FEC's increase from a steady 8 to 20 per second to in some cases over 35,000 per second on certain gateways.
If it is interference surely it can't local to me otherwise I'd see it regardless of gateway?
It seems to happen for an hour or two at a time then suddenly drops back down again, usually in the evenings.
I've just hopped gateway again so let's see if last nights huge increase happens again this evening.
Here's an example from last month when I reported it to Plusnet:
sjrinfroyle
Grafter
Posts: 895
Registered: 08-05-2011

Re: Gateways and FEC errors

I'm sorry but the two are not linked.
If you had no connection to Plusnet and just left the modem in sync with the DSLAM, you'd still get FECs.
Community Veteran
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Registered: 21-01-2013

Re: Gateways and FEC errors

Does the increase in FEC coincide with when your downloading / watching streaming  content ?
As AlecR has said FEC's are corrected errors they are not a significant problem.
At the bottom of your graph it shows "ES/hour: 2.54" this is a much more meaningful measure and that figure of only 2.54 errored seconds per hour is exceptionally good.
As an example my ES/hour averages over 50.
IMO your FEC graph is nothing to worry about.
sjrinfroyle
Grafter
Posts: 895
Registered: 08-05-2011

Re: Gateways and FEC errors

Quote from: npr
Does the increase in FEC coincide with when your downloading / watching streaming  content ?

But like I say throughput on the line wouldn't affect the errors generated. They are generated between your line and the cabinet, and occur whether you're connected to Plusnet's network or not.
But apart from that, what it means is that there's probably some interference on your line at some times of day, which would generate lots of errors but FEC error correction is doing its job and is preventing most of those. It means DLM isn't going to slow your line down or really modify it at all as the other errors are very low indeed.
I'd like to see your QLN and Hlog graphs please, OP Smiley
Haybasha
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Posts: 157
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Registered: 07-05-2014

Re: Gateways and FEC errors

Quote from: npr
Does the increase in FEC coincide with when your downloading / watching streaming  content ?
As AlecR has said FEC's are corrected errors they are not a significant problem.
At the bottom of your graph it shows "ES/hour: 2.54" this is a much more meaningful measure and that figure of only 2.54 errored seconds per hour is exceptionally good.
As an example my ES/hour averages over 50.
IMO your FEC graph is nothing to worry about.


Appreciate your comments, just driving me mad as to why it only happens on some gateways  Huh
No it's doesn't seem to coincide with anything I do online, it can happen when I've just got my PC sitting idle and nothing is going on.
Haybasha
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Registered: 07-05-2014

Re: Gateways and FEC errors

Quote from: AlecR
Quote from: npr
Does the increase in FEC coincide with when your downloading / watching streaming  content ?

But like I say throughput on the line wouldn't affect the errors generated. They are generated between your line and the cabinet, and occur whether you're connected to Plusnet's network or not.
But apart from that, what it means is that there's probably some interference on your line at some times of day, which would generate lots of errors but FEC error correction is doing its job and is preventing most of those. It means DLM isn't going to slow your line down or really modify it at all as the other errors are very low indeed.
I'd like to see your QLN and Hlog graphs please, OP Smiley

Current QLN and HLog attached.
Strange thing is it's at random times of the day and only on certain gateways. If I hop I can be free of high FEC's until PlusNet force be onto another one, just pot luck which I get, like everyone else Smiley
sjrinfroyle
Grafter
Posts: 895
Registered: 08-05-2011

Re: Gateways and FEC errors

So yes you've got some noise on your line, however with the very low error rate, interleaving appears to be doing its job, in fact doing it very well as the error seconds are so low.
In short, I don't think you've got much to worry about Smiley
Haybasha
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Posts: 157
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Registered: 07-05-2014

Re: Gateways and FEC errors

Thanks for the reply, appreciate the comments however it still doesn't explain why it's happening only at random times and on random gateways.
Noise during the day is usually pretty low, rising as expected in the evening but I still get these random bursts of FEC's at all times during the day regardless of noise.
It's all very weird and as an Engineer it's driving me nuts not knowing why  Huh
No huge bursts at all so far this evening since gateway hopping again earlier this afternoon Smiley
dick:quote
jafreer
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Re: Gateways and FEC errors

As has already been said, I think the gateway thing is a red herring. However, there are some things you can do to help trace the noise.
As a previous poster mentioned, VDSL2 only runs between your cabinet and your modem. It doesn't care what gateway you are connected to.
Not convenient, but you can progressively switch electrical items off to try and correlate it with reduction or removal of the noise.
If you use powerline adapters, stop using them and see if the noise is present.
Any switch mode power supplies (e.g. laptop power supplies, mains chargers etc), try and switch them off and monitor for noise.
You could plug the modem and router straight into the master socket and monitor for noise (if not already in the master socket).
It is going to take a bit of detective work, but ignore the gateway stuff for now, and see if you can isolate the noise to internal noise (internal to your house), or external noise.
In my case, I had powerline adapters which were injecting a lot of noise onto the line.
How often to these burst of errors come? (how many times a day on average). Is it worse or better at night? How long does a burst last for?
Best of luck.
Haybasha
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Posts: 157
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Registered: 07-05-2014

Re: Gateways and FEC errors

Thanks for the response, however as already stated this is a totally random event, I've seen it happen each day at random times over several days then not at all for a month or more.
I thought I'd post as it hadn't happened for around 5 weeks then I got a huge spike for over an hour last night, again nothing today.
As an Engineer (who actually manufactures and installs subsea umbilicals for a living) I'm more than competent at using elimination to fault find, this however does not follow any pattern at all.
As for the power line adaptors, not the problem here as I ditched mine well over 2 years ago as they induced so much noise I was losing around 3dB on the SNR with them switched on.
dick:quote
sjrinfroyle
Grafter
Posts: 895
Registered: 08-05-2011

Re: Gateways and FEC errors

It sounds like it might be a REIN issue. The sudden spikes would seem to indicate some level of interference that occurs occasionally.
I had a similar issue a year or so ago, in which my SNRM would drop 1-2dB in a matter of seconds from its target of 6dB. Eventually Openreach came out and a REIN case was created. It took a while but the issue was eventually resolved.
I'm now having other issues (hence why I'm looking to come back to Plusnet) but my connection was better since the OR fix.
I'd like to see your SNRM graph too if you don't mind? Smiley
Community Veteran
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Re: Gateways and FEC errors

is coincidence, the FEC's are unrelated to the PPP gateways.
lf2k
Grafter
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Registered: 12-05-2015

Re: Gateways and FEC errors

As Alec and others have pointed out, the FECs are only happening between your modem and the cabinet - everything else is fibre and in a VPN tunnel (or an equivalent of that).
Random noise on the line could be because of a line fault, or more likely something generating noise between you and the cabinet.
FECs aren't a problem (they're errors that have been corrected and this doesn't penalise your throughput):  ES and SES (errored seconds) are the things to look out for, since these are used by the DLM to decide whether you should be interleaved or if your connection needs to be slowed down to make it more stable.
If it helps, whenever there's any kind of thunderstorm my errors go through the roof - likewise when the neighbour mows the lawn...
Is there any pattern to your Error Seconds?