Very fast ethernets are designed with two modes, standard a standard CSMA/CD bus and a full-duplex collision-free mode. [ .. your lesson on basic networking deleted .. ] ATM since one is stuck playing with forwarding based on only one address space.

Yah, I'm familiar with all this. I'm sitting behind one of those "Bad Notworks" boxes right now, actually.

I'm not sure what flexibility you're referring to wrt ATM vs very fast ethernets, however the latter in combination with software in one particular modern router that isn't completely rocket-science can spoof rate-limited VCs based on MAC addresses, which more-or-less duplicates the one feature of ATM that I happen to like.

Uh.. I'm not sure what you're asking, because I suspect the answer I'm about to give you'd have already considered, no? Ethernet -> Flat. Creating true architectural redundancy isn't possible without separate routes for each connection. Also, even full duplex Ethernet never achieves full bandwidth utilization due to the protocol implementation (hardware protocol). Advantage: All vendors support it, and is usually works without help. ATM -> Flat/Star/Web/whatever. You can create both bandwidth and redundancy without routing. Disadvantage: Every vendor supports it differently, and most of them only have 2 people that really know it. Never works without help. Also, congestion control between hetrogenous systems is a no-op.