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Author Topic: CRCs per unit time on my line 3  (Read 2283 times)

Weaver

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CRCs per unit time on my line 3
« on: February 08, 2021, 03:08:50 AM »
My line 3 has a ZyXEL VMG 1312-B10A with Johnson firmware in it which is a bit slow and slightly sickly with the hollow SNR-vs-tones-graph malaise. It is running at a speed that is somewhat over the top in that the downstream SNR is a bit lower now than the 3dB target that it has been set to have.

Here is the Johnson graph of uncorrected CRC errors per unit time vs time. Too many CRCs per unit time?



I can’t remember what the Johnson graphs ‘unit time’ is, anyone help? I can soon force a resynch to reduce the number of uncorrected CRC errors.
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Alex Atkin UK

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Re: CRCs per unit time on my line 3
« Reply #1 on: February 08, 2021, 12:29:23 PM »
Did you ever compare the old Netgear DG834 to the modern ADSL modems?  As I recall that was the modem of choice on ADSL for a long time.
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Weaver

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Re: CRCs per unit time on my line 3
« Reply #2 on: February 09, 2021, 09:34:18 AM »
No Alex, and I can’t recall why not. That would have been very interesting.

—

So is that too many CRC events? And can anyone remember what the unit of time is?
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Alex Atkin UK

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Re: CRCs per unit time on my line 3
« Reply #3 on: February 09, 2021, 11:08:58 AM »
Isn't the CRC counter corrected packets not uncorrected?
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roseway

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Re: CRCs per unit time on my line 3
« Reply #4 on: February 09, 2021, 11:38:53 AM »
No, FECs are corrected errors, CRCs are uncorrected.
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  Eric

tubaman

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Re: CRCs per unit time on my line 3
« Reply #5 on: February 09, 2021, 12:19:27 PM »
On a VDSL circuit that number of CRCs would likely see DLM action to increase the SNR and hopefully reduce the errors, but your ADSL circuit is clearly not doing that. That volume of CRCs must be reducing throughput as the errored packets will need to be resent.
 :)
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Alex Atkin UK

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Re: CRCs per unit time on my line 3
« Reply #6 on: February 09, 2021, 12:19:43 PM »
Quote from: roseway on February 09, 2021, 11:38:53 AM
No, FECs are corrected errors, CRCs are uncorrected.

Interesting, I could have sworn we'd been saying CRC are irrelevant as they are corrected.  I obviously misunderstood something.
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4candles

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Re: CRCs per unit time on my line 3
« Reply #7 on: February 09, 2021, 12:58:12 PM »
The clue is in the name - Forward Error Correction.   ;)
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ejs

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Re: CRCs per unit time on my line 3
« Reply #8 on: February 09, 2021, 02:01:48 PM »
Apparently the time interval is 30 seconds. I think the error rate is not high enough to adversely affect throughput significantly. If you have to look at the stats and ask the question, rather than notice downloads going slowly, then the answer tends to be no.
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Alex Atkin UK

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Re: CRCs per unit time on my line 3
« Reply #9 on: February 09, 2021, 08:08:27 PM »
Quote from: 4candles on February 09, 2021, 12:58:12 PM
The clue is in the name - Forward Error Correction.   ;)

I blame AstraZeneca, clearly confusion is a side-effect.  :P
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Weaver

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Re: CRCs per unit time on my line 3
« Reply #10 on: February 15, 2021, 03:52:10 PM »
@ejs - thanks for your help.
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