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Author Topic: FEC "signature" Any clues?  (Read 3310 times)

pdes

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FEC "signature" Any clues?
« on: November 17, 2015, 02:46:34 PM »

Team,

My stats are at "pdes" on Mydslwebstats.  Could someone offer an opinion as to whether the bursts of FECs have a recognizable signature?  They always seem to be around the 12000 mark but start and stop very abruptly. While I am experiencing the errors, as you might imagine, my SNR drops then returns to (almost) the original level when the FECs stop.  They seem to be worse in the afternoon.  I have done all the usual tests by turning off appliances, walking round with a de-tuned radio (much to my wife's amusement), watching the power consumption meter in the house to see whether it coincides with something turning on and re-wiring to the incoming socket but have not discovered anything.  Openreach have looked at the circuit a few times by say that all looks and sounds OK.

I would really appreciate an opinion.

Thanks

David
 
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burakkucat

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Re: FEC "signature" Any clues?
« Reply #1 on: November 17, 2015, 05:21:59 PM »

Having taking a quick look at your circuit's statistics, it appears that there is only respite between 0000 - 1000 hours (approximately).

As to what could be causing that interference, it is difficult to say.  :-\  In what sort of environment does the cable, between you and the cabinet, reside? Does it pass by a pub -- one that is open from ten in the morning to midnight, for example?
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pdes

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Re: FEC "signature" Any clues?
« Reply #2 on: November 17, 2015, 05:56:43 PM »

Having taking a quick look at your circuit's statistics, it appears that there is only respite between 0000 - 1000 hours (approximately).

As to what could be causing that interference, it is difficult to say.  :-\  In what sort of environment does the cable, between you and the cabinet, reside? Does it pass by a pub -- one that is open from ten in the morning to midnight, for example?

Thanks for looking. The cable leaves my house and travels 50M underground. Then up a pole and along the road on dropwire for maybe 500M. Then I lose it so assume it us U/G to the cabinet but TBH, I am not sure of the exact run. Funnily enough, I think it crosses the road just before it gets to the local pub!
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pdes

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Re: FEC "signature" Any clues?
« Reply #3 on: December 01, 2015, 11:34:00 AM »

I just took a look at the FEC traces of others but see no patterns like mine.  Everyone else (I looked at around 15) seems to have fairly even patterns with the occassional spike, whereas I seem to have a defined pattern of sudden bursts that last a while then drop just as suddenly.  Could this be some form of cross talk or is indicative of something electrical being switched on and off?.  This is always between 10:00 and around 23:00.  I expect the response wil be that FECs are a good sign but I would dearly love to track down the source as each time there is a burst, my SNR drops.  Do you think Openreach would look at this and take it seriously or am I whistling in the wind?  :-\
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burakkucat

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Re: FEC "signature" Any clues?
« Reply #4 on: December 01, 2015, 06:20:35 PM »

. . . is indicative of something electrical being switched on and off?.  This is always between 10:00 and around 23:00.

As I mentioned, above, it appears that your circuit is afflicted by some form of electrical switching disturbance.

Quote
I expect the response wil be that FECs are a good sign but I would dearly love to track down the source as each time there is a burst, my SNR drops.  Do you think Openreach would look at this and take it seriously or am I whistling in the wind?  :-\

It might be best to regard FECs as "CRCs that never happened". Clearly one does not wish to have CRC errors appearing on a circuit and, by extension, likewise for FECs. However if there has to be a choice and "one type must be present" we would all choose to tolerate FECs rather than CRCs.

I would not expect any assistance to be offered by Openreach in tracing the source of that disturbance.  :no:
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pdes

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Re: FEC "signature" Any clues?
« Reply #5 on: December 02, 2015, 10:42:50 AM »

Appreciate the response.  I suppose I should consider myself relatively lucky as my CRCs are very low especially as I have an Attn of 33.4.  Unfortunately, I only ever get a sync of around 8.5mb at best and I was hoping that to be able to eradicate the FECs may enable a higher speed.  Hey-ho, the joys of living in the sticks! :(
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jelv

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Re: FEC "signature" Any clues?
« Reply #6 on: December 02, 2015, 11:16:56 AM »

Do you have a phone attached to the line?
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pdes

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Re: FEC "signature" Any clues?
« Reply #7 on: December 02, 2015, 11:22:52 AM »

Yes, but wiring is split at the (new) faceplate.  Router is connected directly to the FP
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jelv

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Re: FEC "signature" Any clues?
« Reply #8 on: December 02, 2015, 11:49:55 AM »

That's OK. There's many now who don't have a phone plugged in and so wouldn't realise someone was calling their number (maybe nuisance calls) and hence that the errors were associated with an incoming call. I presume you've checked that errors don't coincide with using the phone?
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pdes

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Re: FEC "signature" Any clues?
« Reply #9 on: December 02, 2015, 12:00:05 PM »

Yep, these are very defined errors every day.  They follow a pattern that starts at around 10:00 in the morning and end around midnight.  Each "spike" is roughly the same shape and volume.  Looks to me like a motor starting, running then shutting down but that's just a wild guess.
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WWWombat

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Re: FEC "signature" Any clues?
« Reply #10 on: December 05, 2015, 11:06:23 AM »

This doesn't help identify the cause, but it gives you more comparison data...

There's an interesting user that you might like to compare yourself to over on this thread:
http://forum.kitz.co.uk/index.php/topic,16512.0.html ("G.INP in full flow").

There, you can see a line that becomes afflicted by FECs from around 10pm through to 3pm, day-in, day-out - but only for the last 10 days or so.

Whatever is causing those FEC's can be tracked further into the other FTTC error-recovery mechanisms: particularly by looking at the G-INP graphs titled "G-retransmit tx", "G-retransmit corr", "G-retransmit UnCorr". Those graphs give an indication of where G.INP is doing its job, and re-transmission is coming into play (retransmission, of course, is another form of "CRC that didn't happen" ... and the "UnCorr"s are the retransmission failures that *do* become CRCs).

Ultimately, the G-LEFTRS graph is the one that identifies when the retransmission mechanism is being called into action too much, with a detrimental impact to throughput. That maxes out at 60 per minute - which "tenbyboy2"'s line does a lot. Your line gets an occasional "1" per minute, so isn't too bad.
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pdes

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Re: FEC "signature" Any clues?
« Reply #11 on: December 05, 2015, 11:14:17 AM »

Many thanks for this. It's so frustrating having access to all that information and not fully understand it but your comments lead me to believe that I do not need to worry unduly.  Although my SNR bounces around, I do not notice service degredation or suffer from re-syncs.  Just wish I could squeeze out a few more Mb!  I guess when I retire in a few weeks, I can spend time boning-up.

Cheers
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WWWombat

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Re: FEC "signature" Any clues?
« Reply #12 on: December 05, 2015, 01:16:52 PM »

When you look at the SNR and FEC graphs side-by-side, you can see two distinct impacts on SNR
- A diurnal rise and fall, around 1dB in amplitude, being lowest from 6pm to 6am.
- The on/off switches of SNR of around 1dB too, which occur anytime between 10am and midnight.

The former doesn't seem to get any corresponding FEC's, but the latter does.

Hence your overall SNR can be 5dB with few FECs (around 1am), but can also be 5dB with lots of FECs (around 1pm).

Definitely odd...
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