IP over ATM overhead

We are installing an ATM backbone connection and wondering what level
of overhead can be expected. ...

I wrote a paper on this subject a couple of years ago. You can find
it at
under "Papers," the title is "Protocol Overhead in IP/ATM Networks",
or at

The level of protocol overhead depends on the medium, the AAL, and the
size of the transmission unit. The best you'll do is to get 87% of the
raw bandwidth to the application (most of this is taken up by the lower
layers (ATM and below)), and this number can go as low as 70%.