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CRC errors

glloyd
Rising Star
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Registered: 06-04-2007

CRC errors

Why am I getting CRC errors when several line test say there are no faults on the line? This has only started happening a couple of months ago.

 

 

12 REPLIES
198kHz
Seasoned Pro
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Registered: 30-07-2008

Re: CRC errors

Virtually all xDSL lines will have some errors - it's all a question of degree. As a rough rule of thumb, the longer the line, the more the errors, though it will depend also on the general quality of the line.

 

Other influencing factors will be crosstalk, proximity to industrial premises and power lines etc, street lights, AM radio interference and so on.

 

How many errors do you average in a day, or a week? Are you experiencing regular re-syncs or dropouts?

Not young enough to know everything
glloyd
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Re: CRC errors

It's random spikes of CRC errors that cause the problems, there is no pattern apart as there are none between midnight and 8.00am.

 

MrSilver
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Re: CRC errors

What problems are you getting? 

CRC errors are just its detected a error on the line and gets resent, if you get too many errors DLM in Openreach will slow the line down a little to reduce the number or errors to make it more stable.

What is it you see as the problem at the PC end or is it more just seeing CRC errors?

glloyd
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Re: CRC errors

My SNR keeps being increased although the router (Fritzbox) is showing few errors. I was actually watching the CRC count when all of a sudden the line was dropped and SNR increased to 12db. It was never that high when we had a line fault. My speed had dropped from 15meg to below 12meg

Superuser
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Re: CRC errors

CRC will be proportional to the volume of traffic on the line, which is possibly why you see a reduction during the hours stated.

However the SNRM shift rather indicates an issue somewhere.  The reported hours could also be linked to other factors ... like Christmas lights being switched off.  Suggest that you explore the usual slow speed investigations (link below) and describe your internal wiring.  Full router stats will be helpful please.

Please perform a quiet line test - dial 17070 select option 2 using a corded phone plugged into the test socket behind the face plate of the master socket. It should be silent. A noisy phone line (or no dial tone) will have a marked adverse impact on the performance of broadband.

If the line is noisy or there is no dial tone, then a PHONE LINE fault needs to be raised with your phone provider. If this is PlusNet, you can report a fault on line using the button below.

Community Veteran
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Re: CRC errors


Townman wrote:

CRC will be proportional to the volume of traffic on the line

No, it isn't.

glloyd
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Re: CRC errors

I've had CRC's ticking up like crazy when there is hardly any traffic.

MrSilver
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Re: CRC errors

Its kind of hard to have no traffic on a DSL link. Even if every devices is turned off the router is sending PPP data down the link, if a PC is on its sending a whole bunch of time checks, anti-virtus checks etc.

 

CRC though is specifically looking at errors in the data that is being sent, if you could get to completely no data at all then you should see  no CRC. If you fill your link that is unstable with 80mb traffic you will see a lot more CRC than just sending 1mb traffic, so there is definitely a relationship between sending traffic on a bad link with the nbumber of CRC errors you will get.

Community Veteran
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Re: CRC errors

The CRC errors are detected at a completely different level to any user Internet traffic. I think technically, a CRC is calculated per ADSL superframe. And if you've got access to stats which include a counter of ADSL superframes, you'll observe that the superframe count increases at a constant rate.

For ADSL, there's also a constant stream of ATM cells, if there's no data to be put into them, empty cells will be sent.

And of course, if you actually have a problem causing a high rate of CRC errors at the DSL level, then you won't be able to transfer data at a high rate.

Superuser
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Re: CRC errors

@ejs,

Not really wanting to pick nits here - though the rate of super frames might be constant, the fuller they are (more bits) then surely that incr ashes the possibility of the frame being 'hit' and therefore requiring recovery?

On that Basis I suggest that there is proportionality, but not necessarily a linear one!

Community Veteran
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Re: CRC errors

The superframes will be of a fixed size. They will be filled with empty cells up to the fixed size. The CRC covers the whole superframe regardless of its contents. The ADSL link is constantly sending and receiving bits at a fixed rate in each direction, only the content of the bits change.

Superuser
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Re: CRC errors

@ejs,

Thank you for the enlightenment - in other words its a bit like running trains, if there are no passengers the train service still runs (empty) as schedule!

 

Have a goo 2017