ATM interface CRC error's issue

[HCL Support]

Hi,

As per our observation, we are getting CRC errors on ATM interface due to Length Violation issue on multiple sub-interface PVCs.

Now attaching here show tech-support of this Router and suggest on this further.

Regards,

Ashutosh

[paolo bevilacqua]

Complain to telco.

For a next time, avoid pointing long attachments, directly include the relevant information only.

[HCL Support]

Hi,

Find below the show interface's output and suggest further as there is no role of telco.

Rt-Noida#sh int atm1/0
ATM1/0 is up, line protocol is up
  Hardware is RS8234 ATM DS3
  Description: "Connected to 9:1.4:4"
  MTU 4470 bytes, sub MTU 4470, BW 45000 Kbit, DLY 190 usec,
     reliability 255/255, txload 48/255, rxload 82/255
  Encapsulation ATM, loopback not set
  Encapsulation(s): AAL5
  1023 maximum active VCs, 21 current VCCs
  VC Auto Creation Disabled.
  VC idle disconnect time: 300 seconds
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 02:59:17
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1774
  Queueing strategy: Per VC Queueing
  30 second input rate 14478000 bits/sec, 9271 packets/sec
  30 second output rate 8475000 bits/sec, 9103 packets/sec
     17802827 packets input, 3039264336 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 1904 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     17537091 packets output, 1920820080 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out

Rt-Noida#sh int atm1/0.24
ATM1/0.24 is up, line protocol is up
  Hardware is RS8234 ATM DS3
  Description: " MCCS WEST NEWLY CONFIGURED PVC "
  Internet address is 10.101.1.1/30
  MTU 4470 bytes, BW 45000 Kbit, DLY 190 usec,
     reliability 255/255, txload 46/255, rxload 80/255
  Encapsulation ATM
  1611732 packets input, 507386098 bytes
  1625980 packets output, 325888322 bytes
  203 OAM cells input, 203 OAM cells output
  AAL5 CRC errors : 1
  AAL5 SAR Timeouts : 0
  AAL5 Oversized SDUs : 0
  AAL5 length violation : 1
  AAL5 CPI Error : 0
  Last clearing of "show interface" counters never
Rt-Noida#

Rt-Noida#sh int atm1/0.33
ATM1/0.33 is up, line protocol is up
  Hardware is RS8234 ATM DS3
  Description: " MCCS SOUTH NEWLY CONFIGURED PVC "
  Internet address is 11.1.1.50/30
  MTU 4470 bytes, BW 45000 Kbit, DLY 190 usec,
     reliability 255/255, txload 44/255, rxload 69/255
  Encapsulation ATM
  2164207 packets input, 620403893 bytes
  2161161 packets output, 433943933 bytes
  210 OAM cells input, 210 OAM cells output
  AAL5 CRC errors : 1903

  AAL5 SAR Timeouts : 0
  AAL5 Oversized SDUs : 0
  AAL5 length violation : 1903

  AAL5 CPI Error : 0
  Last clearing of "show interface" counters never
Rt-Noida#

After checking these output, provide us if there is some workaround for this CRC issue.

[paolo bevilacqua]

The error ratio is small and negligible, and normal in telecommunications.

However again, if you have problem with that, complain to telco. They are the ones that provides you a circuit with some errors.

There is nothing that you can do about circuit errors on a router.

[usujlana]

Allright lets put in other words that Paolo is trying to explain. AAL5 CRC errors are *RECEIVED* errors. its not due to HW issue on your end. if you have done a a HW loopback test then the TELCO needs to see why they are sending errors your way. it could be a host of issue wrong QOS , SCR/PCR etc etc.

Hope this helps.

~Upinder Sujlana

[HCL Support]

There is no Telco exist in current scenario. Router & MGX are approximately 5 meter to each other and BPO using DS3 cable (BNC cable) to connect Router ATM interface with MGX port.

We are not observing any CRC errors on MGX port. Also we are observing length violation issue on PVCs when production is running on them

So kindly suggest any resolution ASAP

[paolo bevilacqua]

Letting ASAP aside

As Upinder has suggested, your QoS settings can cause that some cells are dropped. That can cause AAl5 reassembly failures. You can either configure the router to conform to traffic contract as configured on the BPX, or if the BPX supports frame early drop, that will make it drop rather than sending incomplete frames.

[BRIAN SEKLECKI]

What cmds did you do on MGX to check the interface for CRC errors?

I've been reading the PXM45 documentation for two days and I dont see a command that shows anything about OSI layer1/layer2 details beyond ATM protocol.

dspPort

dspCds etc...

Thanks

~BAS