Intermittent DSL Noise Margin

[johnlloyd_13]

hi all,

we have a DSL link using cisco 877. we've already reported to telco that the link has been intermittent. telco has already re-terminated the link and also changed DSLAM port but issue still persists. i noticed that the noise margin keeps on changing. anyone experienced this? appreciate your advise on how to resolve this kind of issue. thanks in advance!

877>sh dsl int | i Noise

Noise Margin:     7.5 dB                         15.5 dB

877>sh dsl int | i Noise

Noise Margin:    44.0 dB                         15.5 dB

877>sh dsl int | i Noise

Noise Margin:    44.0 dB                         15.5 dB

877>sh dsl int | i Noise

Noise Margin:    14.0 dB                         15.5 dB

877>sh dsl int | i Noise

Noise Margin:    44.0 dB                         15.5 dB

877>sh dsl int | i Noise

Noise Margin:     5.0 dB                         15.5 dB

877>sh dsl int

ATM0

Alcatel 20190 chipset information

                ATU-R (DS)                      ATU-C (US)

Modem Status:    Showtime (DMTDSL_SHOWTIME)

DSL Mode:        ITU G.992.5 (ADSL2+) Annex A

ITU STD NUM:     0x03                            0x2

Chip Vendor ID:  'STMI'                          'BDCM'

Chip Vendor Specific:  0x0000                    0x939E

Chip Vendor Country:   0x0F                      0xB5

Modem Vendor ID: 'CSCO'                          'BDCM'

Modem Vendor Specific: 0x0000                    0x0000

Modem Vendor Country:  0xB5                      0xB5

Serial Number Near:    FHK104516X0

Serial Number Far:    

Modem Version Near:    12.4(9)T1

Modem Version Far:     v09.07.30     

Capacity Used:   14%                             100%

Noise Margin:    44.0 dB                         15.5 dB

Output Power:    13.0 dBm                        12.5 dBm

Attenuation:      3.0 dB                          0.0 dB

Defect Status:   None                            None                       

Last Fail Code:  None

Watchdog Counter: 0x38

Watchdog Resets: 0

Selftest Result: 0x00

Subfunction:     0x00

Interrupts:      7720 (0 spurious)

PHY Access Err:  0

Activations:     1

LED Status:      ON

LED On Time:     100

LED Off Time:    100

Init FW:         embedded

Operation FW:    embedded

FW Version:      2.5.42

                 DS Channel1      DS Channel0   US Channel1       US Channel0

Speed (kbps):             0             3040             0               767

Cells:                    0           399994             0           2441675

Reed-Solomon EC:          0                0             0                 0

CRC Errors:               0                0             0                 0

Header Errors:            0                0             0                 0

Total BER:                0E-0           0E-0

Leakage Avarage BER:      0E-0           0E-0

Interleave Delay:         0               62             0                48

LOM Monitoring : Disabled

[Vaibhava Varma]

HI johnlloyd_13

Recalling from my own DSL experience being in the operator side when we faced such issues reported by customer, one major thing to check was the sanity of the local loop in the last mile.

I hope you would have considered the last mile copper pair in use which is being terminated to the DSL CPE such that the resistance is within limits and no electro-magnetic interference anyhwere in the last mile when the issue occurs. We had one such issue where EMI caused intermittent links at particular hours of the day at the same exact time always.This left us quite puzzled initially but we found the resistance of the line beyond acceptable limits at those times and physical layer troubleshooting led us to a prompt resolution for the issue.I think these factors contribute majorly to the SNR of the local loop.

Hope this helps you in finding the root cause of the issue and finding a deterministic solution. Request you to please share the same on this post which can be a point of learning to us.

Regards

Varma

[johnlloyd_13]

hi varma,

thanks for your insights! i've re-scheduled for a telco tech monday morning to make a thourough check and do proper termination this time. will post again once resolved.

[johnlloyd_13]

just an update, we've checked with the tech there's no physical issue with the link. it turns out there was some sort of spam/dos attack after further checking and monitoring on the router. we've asked our security team to perform a scan/quarantine on the infected machines.

877#sh mem stat hist

100                                                            

90                                                            

80 ************************************************************

70 ************************************************************

60 ************************************************************

50 ************************************************************

40 ************************************************************

30 ************************************************************

20 ************************************************************

10 ************************************************************

   0....5....1....1....2....2....3....3....4....4....5....5....

             0    5    0    5    0    5    0    5    0    5   

               Free memory per second (last 60 seconds)

[paolo bevilacqua]

Before complaining to telco, you should update ADSL firmware.

[johnlloyd_13]

Hi Paolo,

Thanks for the feedback! Appreciate if you could advise me which firmware version is more stable so that I could test.

Sent from Cisco Technical Support iPhone App

[paolo bevilacqua]

Latest version is advisable.

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