[nsp] ATM PVC Shaping Question

From: Martin, Christian (CMartin@mercury.balink.com)
Date: Thu Jun 08 2000 - 13:24:56 EDT


Folks,

OK, I need an answer to this once an for all. Can someone stake their
reputation on answering the following question:

Does a Cisco router using PA-A3 hardware (or NPM-ATM) shape vbr-nrt traffic
based on the cell rate or the payload rate? I hear so many people saying
that it is done based on payload, and they break out these little
calculations to 'account' for the overhead. I cannot fathom that this is
done before SAR. As I see it, the GCRA algorithm is cell-based, therefore,
leaky bucket operations are most efficiently done at a cell boundary. Given
varying lengths of CPCS PDU sizes, I would think that shaping would have to
be done in software were it done based on payload, which obviously would be
a huge performance hit. Unless the SAR chipset does this first? Call me
crazy...

./chris



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