Prompted by Mark Seward, we have had a look at the cell tax incurred for our customers, in those cases where we are unfortunate enough to have to transit an ATM pipe. Which has not been the usual case on our network but becomes interesting for things like UBS. This enables us to answer the question: for a pipe of x bps sufficient to carry pure IP, how much bigger must the ATM PVC be to carry the same load? IP_bw = x ATM_bw = ceiling(x/48)*53 Diff = ATM_bw - IP_bw Cell_tax = Diff/IP_bw For a sample SAMP, we calculate the mean cell tax as (sum(ceiling( SAMP/48)*53) - sum(SAMP))/sum(SAMP) Looking at a 24 hour sample, we get: Upstream: cell tax = 14.84% Downstream: cell tax = 18.35% I understand that this is somewhat at variance with the standard provisioning rules applied by another provider. -- Michael Newbery IP Architect TelstraClear Limited Tel: +64-4-920 3102 Mobile: +64-29-920 3102 Fax: +64-4-920 3361