Anyone encountered Cisco ATM PVC large delay bug?

["Yu Ning" <yuning () cndata com>]

Hi nanog,

I'm not sure how many percentage of global NSP/ISP use ATM PVC to
provide links between their Cisco routers. It seems there is some
large delay bugs in Cisco ATM interface, esp on GSR level routers.

In more detail, our situation is: if we get a high bandwidth PVC,
say 51M(or 80M), and if the bandwidth utilization reaches 80%
percent, the ATM link will encounter a 1500~2000 ms delay - just
point to point ping across the link. We have found this situation 
is associated with "sar txpool" setting in Cisco GSR, and a manipulation
of the "sar txpool" together with bandwidth increasing has solved
the problem now.

But I still wonder if any of you ever encounter this situation(bug),
and how did you overcome it? If you are still puzzled by this bug,
I'd like share our temp solution with you.


regards,

Yu Ning

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(Mr.) Yu Ning 
ChinaNet Backbone Operation
Networking Dep.,Datacom Bureau
China Telecom.,Beijing(100088),P.R.C
+86-10-66418121/66418122/66418123(fax)
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