Question : ATM and OSPF

If OSPF is currently running across a pure IP routed WAN using only routers, how would ATM be implemented in the WAN. Does OSPF run at Layer 3 and ATM run under it at Layer 2 at the SAME time...or does ATM displace OSPF all together.

Answer : ATM and OSPF

ATM runs at Layer 2.  All the IP protocols will run over ATM just as they are running over Frame or Point-to-point links.

To implement ATM in the WAN, you will need an ATM connection to a router, or a switch that is acting as a router (using layer 3 switching, MPLS or any other fancy wire speed routing name vendors have come up with).  You'll also need a connection to the LAN of course, which I assume will be some form of Ethernet.

Then you'll need a carrier connection to their ATM network.  Get everything configured correctly, and your IP network will act as if the ATM part didn't even exist (ie, just like ethernet).