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High FEC/CRC Errors

Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

High FEC/CRC Errors

Hi,
Out of curiosity would the high FEC/CRC errors make a huge difference on my broadband ?
How could I resolve these ?
I'm using a Thomson TG585 v7
Software Release: 7.4.4.7

Uptime: 0 days, 11:38:12  (I restarted the router almost 12 hours ago as I noticed I was on ADSL2 - G.992.3 only and not ADSL2+, a reboot put me back onto G.992.5)
DSL Type: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 444 / 5,335
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 13.0 / 0.0
Line Attenuation (Up/Down) [dB]: 18.5 / 39.0
SN Margin (Up/Down) [dB]: 26.0 / 6.5
Vendor ID (Local/Remote): TMMB / IFTN
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 1 / 0
FEC Errors (Up/Down): 4,294,967,264 / 56,439
CRC Errors (Up/Down): 4,294,967,264 / 99
HEC Errors (Up/Down): 0 / 63

Thanks for any help.
14 REPLIES
ramidoodle
Grafter
Posts: 265
Registered: ‎28-09-2008

Re: High FEC/CRC Errors

Forward Error Correction and Cyclic Redundancy Check are more likely to increase in ADSL2+ than ADSL1 or Max due to implementation of Impulse Noise Protection which uses Reed Solomon algorithm.
ADSL2+ has different levels for interleaving ( INP 0, 1, 2, 4 and 8 ). This means that ADSL2+ Routers are depending heavily on their processors to detect and correct errors instead of retransmitting the data again. This doesn't usually affect your connection throughput but might cause a latency due to the calculations involved at both ends.
Community Veteran
Posts: 3,789
Registered: ‎08-06-2007

Re: High FEC/CRC Errors

Also, those upstream readings are artificially high (a common problem with the TG585) - they're actually representing a negative number.
B.
MrC
Grafter
Posts: 523
Thanks: 2
Registered: ‎17-07-2008

Re: High FEC/CRC Errors

Looks like a firmware bug as 2**32 = 4,294,967,296 = your figures + 32 . Basically the figures are bogus. If the router persistently reports this after reboots then another version of firmware might be the only cure.
Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Quote from: RamiDoodle
This means that ADSL2+ Routers are depending heavily on their processors to detect and correct errors instead of retransmitting the data again. This doesn't usually affect your connection throughput but might cause a latency due to the calculations involved at both ends.

Thanks for the reply RamiDoodle, since the Thomson is depending heavily on the processor to detect and correct errors could this cause the Thomson to overheat and possibly cause the router to reboot on it's own ?
Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Quote from: Barry
Also, those upstream readings are artificially high (a common problem with the TG585) - they're actually representing a negative number.
B.

Thanks for the reply Barry, I was just about to reply concerning the common problem with the TG585 but MrC replied and answered my next question.  Smiley
Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Quote from: MrC
Looks like a firmware bug as 2**32 = 4,294,967,296 = your figures + 32 . Basically the figures are bogus. If the router persistently reports this after reboots then another version of firmware might be the only cure.


Thanks for the reply also MrC, I did notice these errors were no where near as bad before but that's when I also noticed I was on G.992.3 instead of G.992.5 hence my reboot, so these errors only show up when connected to G.992.5 or was that just coincidence ?
MrC
Grafter
Posts: 523
Thanks: 2
Registered: ‎17-07-2008

Re: High FEC/CRC Errors

Quote from: Avalanche
Thanks for the reply also MrC, I did notice these errors were no where near as bad before but that's when I also noticed I was on G.992.3 instead of G.992.5 hence my reboot, so these errors only show up when connected to G.992.5 or was that just coincidence ?
It could be relevant as the firmware may take different code paths when handling and reporting ADSL2+ errors.
If you are feeling adventurous then there are quite a few later firmwares reported for this modem/router on http://download.modem-help.co.uk/mfcs-A/Alcatel/Modems/TG585/v7/Firmware/ and one of these may display more trustworthy error counts. However if your TG585v7 is currently working OK or you're not happy playing around with flashing and reconfiguring then it may be best to just leave it be or perhaps beg/borrow/steal a different make of modem/router Smiley
If you have an issue with connections persistently negotiating at ADSL2 then it might be worth (if you haven't already tried it) plugging your router directly into the test socket on your main BT socket to bypass your home wiring. If you then consistently get ADSL2+ negotiated you know your home wiring may need looking at. If you still get ADSL2 negotiated then it's down to the characteristics of your BT line and not so easy to improve (unless you've got audible noise on the line).
Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Thanks for the reply once again MrC, I'm ok with firmware upgrades so thanks for the link, I'll wait a little longer though before I do that as I wanna keep an eye on my connection, admittedly that was the first time I've seen it negotiating at ADSL2 hence my query with the FEC/CRC errors.
Cheers for the replies once again everyone.
Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Seems my broadband keeps reverting back to ADSL2 rather than ADSL2+, looks like my line cannot handle the higher/different frequencies needed for ADSL2+, I'm unable to get hold of another router for testing purposes but what are the chances of this being a router issue rather than a line issue ?
50/50 or more like 20/80 ?
VileReynard
All Star
Posts: 11,182
Thanks: 305
Fixes: 11
Registered: ‎01-09-2007

Re: High FEC/CRC Errors

Down CRC / HEC errors seem to be the most important - yours are OK.
Try rebooting your router in the daytime - it might just get you into ADSL2+ territory.
Doesn't mean a significantly better speed though.
If you had a different router, you could probably force your noise margin (via software) down a bit to get a small improvement (500kbps).
Is your router plugged into the BT master socket?

Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Thanks for your reply 'A Fox is Evil'.........
Quote from: A
Down CRC / HEC errors seem to be the most important - yours are OK.
Try rebooting your router in the daytime - it might just get you into ADSL2+ territory.
Doesn't mean a significantly better speed though.

I've done this a few times over a few days and although I get ADSL2+ at the time when I check later on in the evening it shows uptime to have disconnected and it's back to ADSL2.

Quote from: A

If you had a different router, you could probably force your noise margin (via software) down a bit to get a small improvement (500kbps).
Is your router plugged into the BT master socket?

I have 2 other spare routers, problem is they are what I upgraded from previously and therefore don't have ADSL2 also the property I live at now does not have a test socket available.

MrC
Grafter
Posts: 523
Thanks: 2
Registered: ‎17-07-2008

Re: High FEC/CRC Errors

Quote from: Avalanche
Seems my broadband keeps reverting back to ADSL2 rather than ADSL2+, looks like my line cannot handle the higher/different frequencies needed for ADSL2+, I'm unable to get hold of another router for testing purposes but what are the chances of this being a router issue rather than a line issue ?
50/50 or more like 20/80 ?

Hard to tell. Plugging your attenuation into http://www.kitz.co.uk/adsl/max_speed_calc.php gives potential sync rates quite a bit higher than what you are seeing, even for ADSL1. As the Thomsons are generally pretty good at negotiating decent sync rates I'd be tempted to point the finger at your wiring, either internal or external. Can you beg/borrow/steal another router to prove this?
What sync, SNR margin and error rates did you get on ADSL1?
VileReynard
All Star
Posts: 11,182
Thanks: 305
Fixes: 11
Registered: ‎01-09-2007

Re: High FEC/CRC Errors

OP has
Quote
Line Attenuation (Up/Down) [dB]:  18.5 / 39.0

Have a look at https://portal.plus.net/support/broadband/speed_guide/broadband_terminology.shtml#dataRate
If you are not close to one of the "break points" - e.g.
Quote
from 5120Kbps  	up to 4.5Mbps
from 5696Kbps  up to 5Mbps

then you may get an increased sync rate - but no increase in actual speed!!!

Avalanche
Grafter
Posts: 34
Registered: ‎23-11-2009

Re: High FEC/CRC Errors

Quote from: MrC
Can you beg/borrow/steal another router to prove this?
What sync, SNR margin and error rates did you get on ADSL1?

I'll try and get hold of another router this week to see what difference it makes. It's hard to say what I got on ADSL1 as I moved premises and when broadband got activated at the new address I had then received my new Thomson router from PlusNet, I'll post back when I test with another router.
Thanks for the replies once again guys.