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Standard User WilliamGrimsley
(committed) Sun 26-Feb-17 21:04:56
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What Are G-LEFTRS?


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Hi guys,

Just noticed a huge spike of noise on my line, no downstream CRC's occured but loads of G-LEFTRS did. Are these G.INP CRC's?

Thanks,

William
Standard User BatBoy
(sensei) Sun 26-Feb-17 21:22:13
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Re: What Are G-LEFTRS?


[re: WilliamGrimsley] [link to this post]
 
LEFTRS = A counter of second-long periods where one or more LEFTR defects were logged. In this sense, it works just like the ES counter does, as a time-based monitor for the number of CRC errors

What does it mean? With CRC's being a thing of the past (anything which used to get a CRC error will now get re-transmitted), I think LEFTRS will be used as the equivalent of ES.
Standard User WilliamGrimsley
(committed) Sun 26-Feb-17 21:27:36
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Re: What Are G-LEFTRS?


[re: BatBoy] [link to this post]
 
I did read that, but I'm still confused. Does that mean now we use G-LEFTRS' and CRC's to work out the ES count? Surely modems should take those into account when collecting ES'?


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Standard User BatBoy
(sensei) Sun 26-Feb-17 21:37:21
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Re: What Are G-LEFTRS?


[re: WilliamGrimsley] [link to this post]
 
With CRC's being a thing of the past (anything which used to get a CRC error will now get re-transmitted)
Standard User WilliamGrimsley
(committed) Sun 26-Feb-17 21:50:43
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Re: What Are G-LEFTRS?


[re: BatBoy] [link to this post]
 
That means they were CRC's but are now being re-transmitted.
Standard User WilliamGrimsley
(committed) Sun 26-Feb-17 22:14:39
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Re: What Are G-LEFTRS?


[re: WilliamGrimsley] [link to this post]
 
I think I get it now, CRC's come from interleaving and G-LEFTRS come from G.INP.

Edited by WilliamGrimsley (Sun 26-Feb-17 22:14:58)

Standard User WWWombat
(knowledge is power) Sun 26-Feb-17 22:52:33
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Re: What Are G-LEFTRS?


[re: WilliamGrimsley] [link to this post]
 
In reply to a post by WilliamGrimsley:
I think I get it now, CRC's come from interleaving and G-LEFTRS come from G.INP.


Nope.

Noise Protection is a layered affair, with multiple ways to try to fix, or otherwise cope with, errors in the underlying bitstream.

The first layer comes from FEC. Interleaving just makes FEC more effective.

Bitstream errors that can't be fixed by FEC are then dealt with by retransmission instead (or, colloquially, G.INP). If the retransmission also fails, then it can be re-retransmitted. More than once, possibly.

If retransmission of a block fails too many times, the modem gives up trying to send it. The missing block then becomes a CRC error.

There are counters that tell you how the various layers are performing in raw numbers: RS, RScorr, Rsuncorr, rtx-tx, rtx-corr, rtx-uncorr, LEFTR, and CRC all show this kind of information.

There are counters that show how often errors are happening, to calculate the "mean time between errors" information. These are FECS, LEFTRS, ES and SES.

So...

- CRCs come from bitstream errors that were severe enough to not be fixed by FEC, and happened every time the data was retransmitted N times, until G.INP gave up.

- LEFTRS come from second-long periods when retransmission was being used *so much* that ordinary throughput was reduced.

Both are a sign of prolonged bursts of noise, but they measure the impact on the line in different ways.
Standard User RobertoS
(elder) Sun 26-Feb-17 23:19:48
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Re: What Are G-LEFTRS?


[re: WilliamGrimsley] [link to this post]
 
CRCs occur on Fast Path as well. Cyclic Redundancy Check. It just says there has been an error in the block. How the modem handles it is a different question.

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Standard User WilliamGrimsley
(committed) Sun 26-Feb-17 23:19:59
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Re: What Are G-LEFTRS?


[re: WWWombat] [link to this post]
 
Understood.

So, do CRC's make a higher impact than G-LEFTRS or vice versa? I presume having decreased throughput is worse?
Standard User WilliamGrimsley
(committed) Sun 26-Feb-17 23:23:59
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Re: What Are G-LEFTRS?


[re: RobertoS] [link to this post]
 
Yes, I know. Sorry, I meant they occurred from failed non-G.INP retransmission.

I presume that when a CRC error occurs from both failed FEC and G.INP retransmission, the noise it occurred from is stronger?

For example, noise that generates 1 CRC with G.INP enabled would likely have been several without G.INP.

Edited by WilliamGrimsley (Sun 26-Feb-17 23:26:40)

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