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Author Topic: FEC and CRC errors  (Read 13231 times)

konrado5

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FEC and CRC errors
« on: August 10, 2013, 01:27:40 PM »

I have ADSL2+ Internet. My router is TP-Link TD-W8950ND. I'd like to check CRC and FEC errors but my router shows only HEC, OCD, LCD, super frame errors. I see CRC errors on ATM tab: AAL5 VCC statitstics but I think these errors are not the ADSL CRC errors shown on other routers. Where could I check CRC and FEC errors?
My router screenshots:
http://img89.imageshack.us/img89/92/rv4m.png
http://img823.imageshack.us/img823/3029/z62a.png
« Last Edit: August 10, 2013, 01:30:27 PM by konrado5 »
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roseway

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Re: FEC and CRC errors
« Reply #1 on: August 10, 2013, 02:43:53 PM »

It appears to be a Broadcom-based router, so

FEC = RS Correctable Errors
CRC = Superframe Errors

Your connection isn't interleaved, so you won't see any FEC errors.

If you want to monitor the connection, I think DSLstats should work with this model if you select the TD-W8960N from the router list.
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  Eric

konrado5

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Re: FEC and CRC errors
« Reply #2 on: August 10, 2013, 04:29:00 PM »

My router haven't Telnet.
What is norm for CRC and HEC errors/12 hours?
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roseway

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Re: FEC and CRC errors
« Reply #3 on: August 10, 2013, 06:35:41 PM »

Apparently you can enable telnet: http://portforward.com/english/routers/port_forwarding/TP-Link/TD-W8950ND/TELNET.htm

There's no norm for CRC and HEC errors. The levels depend on numerous factors. Possibly a more useful indicator is the ES (Errored Seconds) figure. Roughly how many ES do you get in an hour?
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  Eric

konrado5

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Re: FEC and CRC errors
« Reply #4 on: August 10, 2013, 06:56:32 PM »

I have roughly 50-100 ES on 12 hours per 5.0-6.0 snr margin, 250 per 4.4 Db snr margin.
For upstream: about 20 ES on  12 hours but above 100 HEC errors. Sometimes on one second appear 100 HEC errors for upstream.

I can forward port for telnet but I can't enable telnet of the router.
« Last Edit: August 10, 2013, 07:02:24 PM by konrado5 »
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roseway

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Re: FEC and CRC errors
« Reply #5 on: August 10, 2013, 07:34:41 PM »

Quote
I can forward port for telnet but I can't enable telnet of the router.

Port forwarding the telnet port (23) makes the router's telnet server accessible. You should be able to telnet into the router then.

Your levels of ES are quite unremarkable. By comparison, I currently average about 11 ES per hour down and 4 ES per hour up. Occasional short bursts of HECs are also not unusual.

If you can get a monitoring program working to plot the SNR margin it will enable us to see if there's anything which needs attention on your connection. If you can't enable telnet, I understand that Routerstats-Lite works with your router.
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  Eric

konrado5

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Re: FEC and CRC errors
« Reply #6 on: August 11, 2013, 12:04:24 PM »

Port forwarding the telnet port (23) makes the router's telnet server accessible. You should be able to telnet into the router then.
Port forwarding makes the my computer's telnet port accessible from Internet.
Quote from: roseway
Your levels of ES are quite unremarkable. By comparison, I currently average about 11 ES per hour down and 4 ES per hour up. Occasional short bursts of HECs are also not unusual.
What is ideal level of ES on snr margin 6 dB? What is ideal level of ES on snr margin 4 dB?
Quote from: roseway
If you can get a monitoring program working to plot the SNR margin it will enable us to see if there's anything which needs attention on your connection. If you can't enable telnet, I understand that Routerstats-Lite works with your router.
Routerstats-lite works but I use mainly Linux.

I've haven synchronization's break during synchronization. What was it? The problem have disappeared when I have disconnected phone cable connecting master phone socket with second phone socket.
Jul 11 10:40:36 user crit kernel: ADSL G.994 training
Jul 11 10:40:44 user crit kernel: ADSL G.992 started
Jul 11 10:40:48 user crit kernel: ADSL G.992 channel analysis
Jul 11 10:40:54 user crit kernel: ADSL G.992 message exchange
Jul 11 10:40:55 user crit kernel: ADSL link down
Jul 11 10:40:56 user crit kernel: ADSL G.994 training
Jul 11 10:41:04 user crit kernel: ADSL G.992 started
Jul 11 10:41:08 user crit kernel: ADSL G.992 channel analysis
Jul 11 10:41:14 user crit kernel: ADSL G.992 message exchange
Jul 11 10:41:14 user crit kernel: ADSL link up, interleaved, us=1237, ds=17844
 
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roseway

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Re: FEC and CRC errors
« Reply #7 on: August 11, 2013, 01:08:00 PM »

Quote
Port forwarding makes the my computer's telnet port accessible from Internet.

I'm not familiar with your particular router, but you should be able to restrict the port forwarding to the LAN only.

Quote
What is ideal level of ES on snr margin 6 dB? What is ideal level of ES on snr margin 4 dB?

That's impossible to answer. There's no ideal level. The lower it is, the better. But if you consider that there are 3600 seconds in an hour, and (say) 20 ES in an hour, then that's only about 0.55 % of the seconds having errors, which is fairly insignificant.

Quote
Routerstats-lite works but I use mainly Linux.

Routerstats-lite works very well in Linux with Wine.

I'm afraid I can't interpret your log, but it appears that the connection was dropped and quickly restored.
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  Eric

ColinS

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Re: FEC and CRC errors
« Reply #8 on: August 11, 2013, 02:01:07 PM »

As Roseway has said, there is no target for ES per se.  An Error Second is just a second's duration in which at least one unrecoverable (generally CRC) bit error has occurred.  There are various definitions of a S(erious)ES, such as 10 or more consecutive ES, but Asbokid has also suggested a rate of 320 CRCs/s.

If you know the rate of ES, e.g. 1 ES on average every 36s, then you ought to be able to calculate (theoretically) how may bits have been transmitted at your sync rate in that time.  This might give you a lower bound on the BER.  If you also have no SES, then 320 * that figure might give you an upper bound on the BER.

I believe that a BER of 1*10^-8/s is the sort of target error rate used by DLM (i.e. less than that figure is good, more than that bad).
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konrado5

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Re: FEC and CRC errors
« Reply #9 on: August 11, 2013, 02:26:07 PM »

My ISP doesn't use DLM.
roseway: how do you know that super frame errors=CRC errors? I can't find this information in Google.
Screenshots from my router:
http://img89.imageshack.us/img89/92/rv4m.png
http://img40.imageshack.us/img40/5896/asmu.png
« Last Edit: August 11, 2013, 02:35:48 PM by konrado5 »
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ColinS

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Re: FEC and CRC errors
« Reply #10 on: August 11, 2013, 02:29:22 PM »

It's still a typical target error rate, whether or not your ISP uses DLM, and is therefore a more relevant measure of the error rate than ES values.  But feel free to make up your own.
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konrado5

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Re: FEC and CRC errors
« Reply #11 on: August 11, 2013, 02:36:14 PM »

I edited post.
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roseway

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Re: FEC and CRC errors
« Reply #12 on: August 11, 2013, 03:09:43 PM »

Quote
roseway: how do you know that super frame errors=CRC errors? I can't find this information in Google.

By inspecting the stats reported by numerous Broadcom-based routers. All of them report SFErr (superframe errors) and some also report CRCs. In the ones that also report CRCs, the value is always the same as the SFErr value.
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  Eric

konrado5

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Re: FEC and CRC errors
« Reply #13 on: August 11, 2013, 03:12:05 PM »

ADSL BER Test - Result

 The ADSL BER test completed successfully.
Test Time (sec):   360
Total Transferred Bits:   0x000000015B641800
Total Error Bits:   0x0000000000000000
Error Ratio:   0.00e+00

ADSL BER Test - Result

 The ADSL BER test completed successfully.
Test Time (sec):   360
Total Transferred Bits:   0x000000015B641800
Total Error Bits:   0x0000000000000000
Error Ratio:   0.00e+00

ADSL BER Test - Result

 The ADSL BER test completed successfully.
Test Time (sec):   360
Total Transferred Bits:   0x000000015B641800
Total Error Bits:   0x0000000000000000
Error Ratio:   0.00e+00

ADSL BER Test - Result

 The ADSL BER test completed successfully.
Test Time (sec):   360
Total Transferred Bits:   0x000000015B641800
Total Error Bits:   0x0000000000000089
Error Ratio:   2.35e-08
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konrado5

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Re: FEC and CRC errors
« Reply #14 on: August 11, 2013, 03:20:19 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.
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