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Author Topic: FEC and CRC errors  (Read 13230 times)

kitz

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Re: FEC and CRC errors
« Reply #15 on: August 11, 2013, 03:41:32 PM »

Are HEC and bit errors for upload downloded from DSLAM? I've seen that number of HEC and bit errors for upload doesn't erase after router's reboot.

This is a weird one, and something that Ive never seem to have been able to get to the bottom of.   To this day I dont think anyone knows for sure one way or other.

Going back about 5 yrs I was trying to find a way to reset these errors.  (Theres a few threads on here about it). 
On the ST585v6 it used to save the upload error figures and somewhere retained in memory.  There is/was no way to do a reset.  For a while it was assumed to be a firmware issue...   and later it was assumed that these figures were being stored on the DSLAM as there were a couple of broadcom based routers that were reproducing these figures.  Then it was seen to be a profile related issue that could be reproduced..  ie a change of line profile via the router could reset them, but go back to the old profile and they would be back again.

However a complete change of router would often reset these figures to 0  ???



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Edit to add link to one of the threads on this topic
 
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konrado5

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Re: FEC and CRC errors
« Reply #16 on: August 11, 2013, 04:23:49 PM »

I've had much bit and HEC errors for upload on the first run of the TP-Link TD-W8950ND. My router showed 0 errors when my ISP rebooted DSLAM port.
Quote from: kitz
However a complete change of router would often reset these figures to 0
Perhaps some routers doesn't show bit errors from time of run DSLAM.

I have another problem. There is changing snr margin of the upload. At the one synchronization I've 5.0-5.5 dB snr margin and output power 12.4 dB and at that moment I've resynchronizate and I've much higher snr margin 6.6-6.8 dB and lower output power 5.9 dB. Is it problem with snr margin measure for upload? My router and DSLAM don't know what are conditions on line? It's strange that the results of snr margin measue depend on concrete synchronization and not only of speed and time.



« Last Edit: August 11, 2013, 05:19:20 PM by konrado5 »
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kitz

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Re: FEC and CRC errors
« Reply #17 on: August 12, 2013, 12:10:01 PM »

>> Perhaps some routers doesn't show bit errors from time of run DSLAM.

Not all show 'bit errors', but they will usually show HEC/CRC/FEC type errors.


>>> There is changing snr margin of the upload

Sorry not quite sure if I understand what you are getting at here?


However, if you mean changing at sync time... Thats not unusual as you are capable of reaching the max 1.2Mbps on adsl2+.
 
When the line rate reaches the maximum DSLAM configured speed then adjustments can be made to the power output.  This is done on purpose to avoid crosstalk affecting longer lines.  If your power output is reduced, then naturally it will affect your SNRm.  This is called Power Cutback and its a deliberate feature of adsl.

So in your case if you are able to sync at the maximum configured speed at a default target SNRm of 6dB or above, then the MSAN will apply power cutback (hence you see 5.9 dBm for power).  Dont worry though.. because if line conditions get bad, then it should easily be able to up the juice again.
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konrado5

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Re: FEC and CRC errors
« Reply #18 on: August 12, 2013, 12:43:16 PM »

I have snr margin 5.3 dB per 1261 kbps and power output 12.4 dBm. I'm restarting router and I have higher snr margin 6.8 dB per 1277 kbps and power output 11.9 dBm. I wonder what is cause of these differences of snr margin measure. I think that lower power output cause lower snr margin. Can't devices correctly measue snr margin? Is it possible to increase snr margin by new synchronization?

I can reset HEC error statistics for upload but I can't reset bit errors for upload. However if I reboot the router it shows many HEC errors for upload to the time while I reset these statistics.
My router doesn't show any bit errors for downlad unless I do ADSL BER test.
« Last Edit: August 12, 2013, 12:48:32 PM by konrado5 »
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kitz

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Re: FEC and CRC errors
« Reply #19 on: August 13, 2013, 06:17:38 PM »

Quote
I didn't get reply

http://forum.kitz.co.uk/index.php/topic,12783.15.html

Possibly because Ive not been here all day & had other things to do...  I havent even had chance yet to sort out my own line fault.
Please be aware that every one here volunteers their time, theres a good bunch of people on here who will always answer if they can.

PMing me 3 times every time you dont get a response wont get you a quicker reply

Now excuse me..  Im going to get some food as Ive not eaten all day.
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kitz

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Re: FEC and CRC errors
« Reply #20 on: August 13, 2013, 08:37:00 PM »

I did see your post this morning.  I just didnt have time to type a reply before I had to go out, because I knew it wasnt a 2 minute reply. :/


>>> I wonder what is cause of these differences of snr margin measure.


SNRm fluctuations are normal, I've passed the links a few times before for SNR, SNR Margin & Target SNR.  If you have a read here it may help you to understand what is going on.

>>> I think that lower power output cause lower snr margin.

As mentioned above,  power output will have an effect on your SNRm & Increasing the power output will increase SNR figures, so yes you are correct in that lower output power will cause lower SNR.   However bear in mind that SNRm fluctuates normally without changes in power.   The Power cut back is there to prevent SNRm getting to high and your signal getting too strong and drowning out neighbouring signals.   

There are certain power cut back profiles, however no-one knows what the power cut back parameters actually are.  They are an adsl standard that has to be there, but are industry standard masks and profiles which may vary from country to country and line length.

>>> Can't devices correctly measue snr margin?

Devices do a pretty good job at measuring the Signal to Noise RAtio, so yes the SNR Margin should be fairly accurate.


>>> Is it possible to increase snr margin by new synchronization?

Yes and No

On the face of it, it may appear to change as your router reports it..  but the reality is, that because its linked to your REAL SNR which definitely isnt affected by new syncs, all youve done is adjust other parameters so that the SNRm gets as near as possible to the Target SNR.

Resync is one of the times when you may see a change in power output though, as this is one of the times when a check is made to ensure your signal isnt too strong.
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konrado5

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Re: FEC and CRC errors
« Reply #21 on: August 13, 2013, 10:49:33 PM »

Sorry, English is not my first language and you didn't understand me. I have situation:
upload 1257 kbps snr margin 5.3 dB power output 12.4 dB and I disconnect.  20 seconds later: upload 1277 kbps snr margin 6.8 dB power ouput 11.9 dB therefore higher snr margin despire raised synchronization and lowered power output. I think that DSLAM can't correctly measure snr margin. Snr margin for upload is stable but new synchronization=new snr margin measurements. I'm afraid that sometimes DSLAM gives too much output power because snr margin for upload is bad measured (lower than in reality).
« Last Edit: August 13, 2013, 11:21:19 PM by konrado5 »
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