ATM interface errors

[chris morris]

Does anyone know why I might receive AAL5 length violation errors but not oversize SDU errors:

MTU 4470 bytes, BW 3840 Kbit, DLY 20000 usec,

reliability 255/255, txload 68/255, rxload 42/255

Encapsulation ATM

23035716 packets input, 10690163751 bytes

18204104 packets output, 6438110443 bytes

0 OAM cells input, 0 OAM cells output

AAL5 CRC errors : 3342

AAL5 SAR Timeouts : 0

AAL5 Oversized SDUs : 0

AAL5 length violation : 3317

AAL5 CPI Error : 0

[lgijssel]

If the number of errors here is not increasing, forget about it. You are talking roughly 3000 packets out of 23 million that's one in 7000 or 0,014%! Nothing to really worry about.

Regards,

Leo

[pkhatri]

Hi Christopher,

A common scenario where this may occur is where you are traversing an ATM switch which happens to drop some cells (because of policing and/or congestion). When the router attempts to re-assemble the AAL5 frame, the size of the resulting frame is smaller than what is indicated by the Length field in the AAL5 trailer. That is when you get such errors. In fact, this also results in CRC errors which you can also see. An over-sized SDU would be one that is larger than the maximum AAL5 frame that your router is capable of receiving. That is a different sort of error to what you are seeing.

Hope that helps - pls rate the post if it does.

Paresh