Big latency on CISCO 7200 ATM circuit

I've got a CISCO 7200 with ATM 4MB. I've started noting that when the
circuit gets to 3.2Mb, the delays start to be high (200ms), and when
the circuit tops at 3.6Mb, the delay can be one second or above. I can
understand the delay when it tops due to queueing, but not when it is
below the maximum usage. Haven't seen great drops nor retransmisions.
Have gone through the conf, but nothing suspicious. Any ideas?
rj

 

Hello, Raymond!
You wrote on 15 Dec 2003 15:51:04 -0800:

RJ> I've got a CISCO 7200 with ATM 4MB. I've started noting that
RJ> when the circuit gets to 3.2Mb, the delays start to be high
RJ> (200ms), and when the circuit tops at 3.6Mb, the delay can be
RJ> one second or above. I can understand the delay when it tops
RJ> due to queueing, but not when it is below the maximum usage.
RJ> Haven't seen great drops nor retransmisions.
RJ> Have gone through the conf, but nothing suspicious. Any ideas?
RJ> rj

Did you check with the carrier PCR, SCR and MBS settings? We had precisely the
same problem - RTT around 1s - when carrier had VBR-nrt class of service
configured on their switches with 3Mbps PCR and 1.5Mbps SCR, and another group
of the same company configured UBR with 3Mbps PCR on our routers.

"show atm pvc" would be helpful.

With best regards,
Andrey.

 

What type of ATM module is installed? Have you looked at the memory?
Look for buffer overruns. You mentioned queueing. Are you running
any sort of QOS on the circuit? How is the PVC configured; VBR-RT,
VBR-NRT, ABR. Make sure you and the provider have the same settings
on the PVC; PCR, SCR, MBR.
A misconfiguration on you PVC in the cloud my be the cause of your
issue.

 

Yes, I've seen the same thing Andrey! Raymond, your carrier most likely
misconfigured the PVC.

Mike