North American Network Operators Group
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Re: Anyone encountered Cisco ATM PVC large delay bug?

  • From: Alexei Roudnev
  • Date: Sun Apr 23 04:44:48 2000 
I think, the clue is in your accounting - you have 100% used bandwidth when you propose 80%. 
ATM bandwidth is a pretty twisted thing.

If so, some queueries appear and it explain the delays.

----- Original Message ----- 
From: "Yu Ning" <[email protected]>
To: "Alex Rubenstein" <[email protected]>
Cc: "nanog-post" <[email protected]>
Sent: Thursday, April 20, 2000 5:06 PM
Subject: Re: Anyone encountered Cisco ATM PVC large delay bug?


> Hi,
> 
> ----- Original Message ----- 
> From: Alex Rubenstein <[email protected]>
> To: Yu Ning <[email protected]>
> Cc: nanog-post <[email protected]>
> Sent: Friday, April 21, 2000 8:01 AM
> Subject: Re: Anyone encountered Cisco ATM PVC large delay bug?
> 
> 
> > 
> > 
> > 
> > Are you accounting for ATM overhead? Remember, the sho in bits/sec do NOT
> > count overhead (another words, they are looking at true bits/sec, not
> > cells/sec).
> > 
> > You should check cells/sec on the ATM port you are connected to.
> > 
> Yes. I get the utilization statistic from ATM PVC statistic.
> 
> 
> > 
> > 
> > 
> > > 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
> > > 
> > > -------------------------------------------
> > > (Mr.) Yu Ning 
> > > ChinaNet Backbone Operation
> > > Networking Dep.,Datacom Bureau
> > > China Telecom.,Beijing(100088),P.R.C
> > > +86-10-66418121/66418122/66418123(fax)
> > > -------------------------------------------
> > > 
> > 
> > 
>