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CRC Errors on VDSL Controller but no corresponding packet loss or interface error

Hello All,

I'm somewhat confused by what I am seeing on several of our Edge network routers.  They are Cisco 887VA routers with the built in DSL Modem and we have just recently started monitoring the DSL line statistics with SNMP and have noticed an odd issue. 

When I do a show controllers vdsl 0 command I am seeing crc errors in the line stats (see below), however the speed and noise margins are within acceptable limits.  These statistics were generated over the last ~24 hours.  However, I am not seeing any associated packet loss within our monitoring tools or errors on the ATM interface.  I have the issue on multiple devices and there are two different versions of firmware running on the controller A2pv6C032b.d23i and A2pv6C035j0.d23j


show controllers vdsl 0
Controller VDSL 0 is UP
Daemon Status:           Up
                        XTU-R (DS)              XTU-C (US)
Chip Vendor ID:         'BDCM'                   'ALCB'
Chip Vendor Specific:   0x0000                   0x0000
Chip Vendor Country:    0xB500                   0xB500
Modem Vendor ID:        'CSCO'                   '    '
Modem Vendor Specific:  0x4602                   0x0000
Modem Vendor Country:   0xB500                   0x0000
Serial Number Near:    FGL1604208T 887VA-SE 15.1(4)M
Serial Number Far:
Modem Version Near:    15.1(4)M
Modem Version Far:     0x0000

Modem Status:            TC Sync (Showtime!)
DSL Config Mode:         AUTO
Trained Mode:            G.992.1 (ADSL) Annex A
TC Mode:                 ATM
Selftest Result:         0x00
DELT configuration:      disabled
DELT state:              not running
Trellis:                 ON                       ON
Line Attenuation:        38.0 dB                 21.0 dB
Signal Attenuation:      38.0 dB                  0.0 dB
Noise Margin:            13.8 dB                  9.0 dB
Attainable Rate:        5864 kbits/s             992 kbits/s
Actual Power:            19.8 dBm                11.9 dBm
Total FECS:             0                        0
Total ES:               9912                     0
Total SES:              1                        0
Total LOSS:             0                        0
Total UAS:              0                        0
Total LPRS:             0                        0
Total LOFS:             0                        0
Total LOLS:             0                        0
Bit swap:               0                        0

Full inits:             1
Failed full inits:      0
Short inits:            0
Failed short inits:     0

Firmware        Source          File Name (version)
--------        ------          -------------------
VDSL            embedded        VDSL_LINUX_DEV_01212008 (1)

Modem FW  Version:      110506_1916-4.02L.03.A2pv6C032b.d23i
Modem PHY Version:      A2pv6C032b.d23i

                  DS Channel1     DS Channel0   US Channel1       US Channel0
Speed (kbps):             0             3488             0               800
Previous Speed:           0                0             0                 0
Total Cells:              0        828929669             0                 0
User Cells:               0         10906583             0                 0
Reed-Solomon EC:          0                0             0                 0
CRC Errors:               0            12169             0                 0
Header Errors:            0             1958             0                12
Interleave (ms):       0.00             0.25          0.00              0.25
Actual INP:            0.00             0.00          0.00              0.00

Training Log :  Stopped
Training Log Filename : flash:vdsllog.bin


Does anyone have any suggestions as to what might be causing these errors, I am just looking to understand what is happening, despite the fact that it does not seem to be having an impact on network quality.  


Everyone's tags (1)

ADSL/VDSL modems operate

ADSL/VDSL modems operate below the level of IOS for their low-level communications, so you're not going to see these sorts of errors on the interface because they don't translate directly to a framing or packet error.

Because you're going over standard phone lines, you're going to see the occasional glitch in communications, which the ADSL/VDSL modem is designed to account for. As long as these errors aren't a higher percentage of your total traffic, it's fairly normal.

In this case, you're seeing errors at .01% of your total cell transfer, so you've got a very clean line.

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