[c-nsp] how to validate cell rates?

[Gert Doering]

Hi,

we have an interesting problem here (as usual, a Telco is involved)...

Customer has an SDSL line, which is handed to us as an ATM PVC with
ATM AAL5 SNAP encapsulation (customer side is bridged to ethernet by
the Telco termination device).

Our side is configured to use "ubr 2303", which translates to
5432 cells/second ("show atm vc <name>").  Which is exactly the cell 
rate that we are permitted to use (actually it's 5433 c/s, but you 
can't configure that on Cisco gear - ubr 2304 translates to 5434 c/s)

Our gear is a 7206 with 12.3(9) and an PA-A3-OC3SMI.

Now the line drops packets.  Open ticket with Telco, telco claims 
"you are sending too much data, we see up to 5600 cells/seconds, so
our ATM switches drop cells due to policing".

We have *never* seen this with lots of ADSL lines on the same router,
also handed off as ATM PVCs (some aal5mux ip, some aal5snap), so I'm
not really willing to believe their claims - I'm more willing to assume
some misconfiguration on their end.  But I can't prove that.

So my question is: is there a way to find out peak cell rate on a given
PVC?  Or are there any known bugs in 12.3(x) with PA-A3s that could 
result in the router exceeding the configured PCR?

Maybe it's just a question of measurement intervals (like "Cisco calculating
PCR on a per-second basis, while Telco gear polices on a per-0.5-second
basis")?  Do the ATM standards specify on which time base PCR has to be 
calculated?

thanks,

gert


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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de