ATM link CRC errors

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Jul 29th, 2008
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I have ATM link in UK facing CRC errors.

How can i check the impact of errors on input and output packet drops?

should i consider the errors.

What troubleshooting needs to done to clear it.

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gojericho0 Tue, 07/29/2008 - 04:25
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Are the errors still incrementing?


How long ago have you noticed this and have you had any complaints?


What is the percentage of errors when compared to total packets sent?


Are you receiving any other type of errors besides CRC? (if possible display sh atm int)


CRC could be caused by a lot of things...anything from a full circuit to bad cable ends.


gajanangavli Tue, 07/29/2008 - 04:31
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sh int atM 0/2/0

ATM0/2/0 is up, line protocol is up

Hardware is ATM AIM E1

MTU 4470 bytes, sub MTU 4470, BW 1920 Kbit, DLY 20000 usec,

reliability 255/255, txload 8/255, rxload 5/255

Encapsulation ATM, loopback not set

Encapsulation(s): AAL5

255 maximum active VCs, 256 VCs per VP, 1 current VCCs

VC Auto Creation Disabled.

VC idle disconnect time: 300 seconds

Last input 04:45:52, output 00:00:00, output hang never

Last clearing of "show interface" counters 02:20:19

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: Per VC Queueing

5 minute input rate 44000 bits/sec, 65 packets/sec

5 minute output rate 64000 bits/sec, 101 packets/sec

703753 packets input, 79519246 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 1470 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

1054209 packets output, 88413441 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

-----------------------------------------

sh controllers atM 0/2/0

Interface ATM0/2/0 is up

Hardware is ATM AIM E1 connected to AIM slot 0

hwidb=0x444D7E70, sardb=0x449DA880

slot 0, unit 0, subunit 0

MXT5100 versions: Framework 0x3383, Utils 0x3383,

AAL5 0x3383, AAL2 0x3383, AAL1 0x3383,

IMA 0x3383, CS 0x3383, Frame 0x3383.

Current (mxt5100_t)sardb:

Ind_Q(0xF7F63C0), Ind_Q_idx(237), Ind_Q_size(30000)

Cmd_Q(0xF7F1560), Cmd_Q_idx(516), Cmd_Q_size(20000)

Inpool(0xF7BB080), Inpool_size(4096)

Outpool(0xF7BC0C0), Outpool_size(4096)

Localpool(0xF7C0000), Localpool_size(256)

StorBlk(0xF647000), host_blk(0xF644520), em_blk(0xF6445E0)

tx_buf_desc(0xF7EA4E0), tx_free_desc_idx (1023)

MXT5100 sub_channel_mode is disabled

MXT5100 number of buffers in Inpool: 1024, Outpool 0

FPGA revision 0x20700F1

MXT5100 Port Info:

Port Number (0), Port ID (0xE05)

Interface Number (4), Interface ID (0x12E1)

Port Type CELL, Port Open Status SUCCESS

VCs configured (1)

Port counters: tx_cells 181571553, rx_cells 266865608,

rx_hec_errors 23708, rx_cell_validation_errors 23702

Cell delineation PRESENT

Times cell delineation has been lost 20667

MXT5100 Channel Info:

Channel Info (0):

Chan_ID (0xF25), Open Status SUCCESS, VC(8)VPI/VCI(1/46),

Tx Ring packets(used/max 0/40), Tx SBD(used/max 0/40)

Tx PDU(49544928), Tx PDU discard(0)

Tx SDU size err(0), Tx cell CLP0(104388997), Tx cell CLP1(0)

Rx PDU(37058639), Rx PDU discard(0), Rx SDU size err(1517)

Rx CRC err(124916), Rx cell CLP0(160858303), Rx cell CLP1(0)

--------------------------------------

sh int atM 0/2/0.1

ATM0/2/0.1 is up, line protocol is up

Hardware is ATM AIM E1

Description: Management PVC

Internet address is A.B.C.D/30

MTU 4470 bytes, BW 1920 Kbit, DLY 20000 usec,

reliability 255/255, txload 5/255, rxload 3/255

Encapsulation ATM

708155 packets input, 79934749 bytes

1060067 packets output, 88853953 bytes

859 OAM cells input, 859 OAM cells output

AAL5 CRC errors : 1470

AAL5 SAR Timeouts : 0

AAL5 Oversized SDUs : 17

Last clearing of "show interface" counters 02:22:29




gojericho0 Tue, 07/29/2008 - 04:37
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Clear your counters and wait 5 minutes. Then check a couple times if its incrementing. If it is not I would say the line has cleared up and you have nothing to worry about.


Your error rate right now is well below 1% when comparing CRCs to total packets. This will not effect performance at all

gajanangavli Tue, 07/29/2008 - 04:44
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After 5 min i m getting 5 CRC errors, i think these errors occur when there is traffic on link only . how can i make it to zero.

gojericho0 Tue, 07/29/2008 - 04:52
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Are these occuring all the time?


Is this a new circuit?


Did the circuit always have CRC errors or just recently?


Some things to start with include checking with the provider to check if the atm cloud is congested or if they have dropped any frames recently to your PVC.


If those things check out ok, you can also attempt changing connections to your router to see if you may have bad/loose cable pair.


You can also create a loopback on the atm interface to see if that is bad and ping it for awhile. The pings will fail, but when you do a sh atm you will see traffic statistics.


If any of this helps pls rate for others



gajanangavli Tue, 07/29/2008 - 05:02
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when there is traffic, error occurs.

yes this is new ckt.

when i do the test loopback in offproduction hrs?

As i think errors are on atm 0/2/0.1 it is clearly that these are not media or cable problem.

Which factor should i check on isp router for my pvc , that will show me conjestion or packet drop.

Can i check policing on both end.


gojericho0 Tue, 07/29/2008 - 05:12
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you would do the loopback in a maintenance window because it will not pass any traffic


i still wouldn't rule out a physical circuit problem since it looks like you only have 1 pvc


you can and should check policing on both ends. if you give you ISP the circuit ID they should be able to perform some testing as well. just make sure no intrusive testing is done during production.

gajanangavli Tue, 07/29/2008 - 05:17
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Thanks for your help.

i will check the below points

1) policing on both end.

2) Conjestion in provider network if possible


gajanangavli Wed, 07/30/2008 - 00:05
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I have got configuration of both router for atm interface


A END


interface ATM0/2/0.1 point-to-point

description Management PVC

ip address A.B.C.D 255.255.255.252

no snmp trap link-status

pvc 1/46

vbr-nrt 1920 1024 100

no oam-pvc manage

encapsulation aal5snap


B END

interface ATM2/0.46 point-to-point

bandwidth 2000

ip address E.F.G.H 255.255.255.252

no snmp trap link-status

pvc 1/46

vbr-nrt 1920 1024 100

oam-pvc manage

encapsulation aal5snap


I M not getting this OAM term and bandwidth which is different on both side.

Is any mismatch in configuration



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