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Technical News & Discussion => Broadband, Internet & General Computer News & Discussion => Topic started by: klipp on Sep 09, 2010, 21:45:25

Title: What are RX CRC errors?
Post by: klipp on Sep 09, 2010, 21:45:25
...and more to the point are they bad news?

(http://i53.tinypic.com/24evmti.jpg)
Title: Re: What are RX CRC errors?
Post by: Steve on Sep 09, 2010, 21:57:43
Received cyclical redundancy check

I'm not up on the maths or the network technolgy to give a complete explanation but its a method of verifying the integrity of a piece of data. In simplistic terms is the piece of data that's arrived (at the router in your case) the same as the data that I am expecting. Does it matter? Well no if it is only a small percentage of the data received. If the CRC are a high percentage, I have read greater than 1% then throughput will be reduced as that piece of data which is wrong has to be re requested.


I hope that's clearer than mud ;D
Title: Re: What are RX CRC errors?
Post by: klipp on Sep 09, 2010, 22:04:47
Thanks Steve for your explanation.  So what you're saying is, of the 150 million RX cells I've received, 176 had an issue of some kind?
Title: Re: What are RX CRC errors?
Post by: Steve on Sep 09, 2010, 22:07:03
Yes and it's very small percentage.
Title: Re: What are RX CRC errors?
Post by: klipp on Sep 09, 2010, 22:12:48
Okies, I'll ignore it then.  I should stop looking for problems really LOL.  I was checking if my SNR had been lowered yet (it has!!  ;D), when I spotted the RX CRC errors and it got me wondering.  Thanks Steve.
Title: Re: What are RX CRC errors?
Post by: DorsetBoy on Sep 10, 2010, 06:34:12
I see a problem in your image straight away , you are running on Adsl2 mode G.992.3  where your connection will surely be ADSL2+ which is G.992.5 .

You can either manually set G992.5 mode or go to Multimode which should select ADSL2+ for you.
Title: Re: What are RX CRC errors?
Post by: Steve on Sep 10, 2010, 06:57:51
Perhaps that's why it's 'stable'?  ;)
Title: Re: What are RX CRC errors?
Post by: Steve on Sep 10, 2010, 09:42:33
Not sure whether I'd advise correcting the adsl mode "If it aint broke don't fix it springs to mind" especially after your line troubles recently.
Title: Re: What are RX CRC errors?
Post by: DorsetBoy on Sep 10, 2010, 09:48:49
On the other hand the router will never negotiate the line correctly if it is set in the wrong mode..........
Title: Re: What are RX CRC errors?
Post by: Steve on Sep 10, 2010, 09:53:32
I not disagreeing Dorset but I've seen a few posts on the net where people on long lines have gained stability on ADSL2+ by using ADSL2 mode. I suppose the answer is to try the correct mode knowing there is something perhaps to fall back on.
Title: Re: What are RX CRC errors?
Post by: DorsetBoy on Sep 10, 2010, 10:24:51
You are right Steve, in fact on the Sky forum a staff member suggested using GDMT on long lines where ADSL2+ was a pain due to noise/instability, he said to use the Max settings to get a lower stable synch.

It's just that people often say their speed/synch are not what they should be or were, often it is just the mode setting being wrong, ADSL2 and 2+ are quite different in throughput.
Title: Re: What are RX CRC errors?
Post by: klipp on Sep 10, 2010, 12:35:21
Hi,

Yes I'd noticed already that I have ADSL2 rather than ADSL2+.  This is what multimode decides I should be using.  I tried manually overriding it by selecting ADSL2+ but I kept losing sync and also my Line Attenuation jumped from 53db to 57db.  After putting it back onto multimode again my Line Attenuation dropped back to 53db but my SNR rose to 15db which is why my downstream rate is kinda low.  It looks like my SNR has finally dropped back down now and things seem to be stable again.  I might try a restart later on to see if I get a better sync rate.
Title: Re: What are RX CRC errors?
Post by: Rik on Sep 10, 2010, 12:36:50
Do it tomorrow morning, klipp, later is bad for speed. :)
Title: Re: What are RX CRC errors?
Post by: klipp on Sep 10, 2010, 12:42:36
Well Rik, my SNR increases to 4db~5db during the day right now, but from kinda 10pm onwards it drops to 2db~3db.  Would it be better (stability wise) to try a resync at the higher or lower SNR value?  Or wouldn't it make any difference?
Title: Re: What are RX CRC errors?
Post by: Rik on Sep 10, 2010, 12:51:50
If you want stability, resync on the lowest NM. If you want speed, do it on the highest (usually morning).